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GALILEO
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WALLACE BROCKWAY, Executive Editor
On the Loadstone and Magnetic Bodies
BY WILLIAM GILBERT
Concerning the Two New Sciences
BY GALILEO GALILEI
On the Motion of the Heart and Blood
in Animals. On the Circulation of the
Blood On the Generation of Animals
BY WILLIAM HARVEY
WILLIAM BENTON, Publisher
ENCYCLOP/EDIA BRITANNICA, INC.
CHICAGO • LONDON • TORONTO
On the Loadstone and Magnetic Bodies, translated by P. Fleury Mottelay,
is reprinted by arrangement with JOHN WILEY AND SONS, INC.
Dialogues Concerning the Two New Sciences, translated by Henry Crew and Alfonso de Salvio,
is reprinted by arrangement with NORTHWESTERN UNIVERSITY STUDIES
COPYRIGHT IN THE UNITED STATES OF AMERICA, 1952,
BY ENCYCLOPEDIA BRITANNICA, INC.
COPYRIGHT 1952. COPYRIGHT UNDER INTERNATIONAL COPYRIGHT UNION BY
ENCYCLOPEDIA BRITANNICA, INC. ALL RIGHTS RESERVED UNDER PAN AMERICAN
COPYRIGHT CONVENTIONS BY ENCYCLOPEDIA BRITANNICA, INC.
GENERAL CONTENTS
On the Loadstone and Magnetic Bodies and on
the Great Magnet the Earth, Page i
By William Gilbert
Translated by P. Fleury Mottelay
Dialogues Concerning the Two New Sciences, Page
A By Galileo Galilei
Translated by Henry Crew and Alfonso de Salvio
An Anatomical Disquisition on the Motion of
the Heart and Blood in Animals, Page 2.67
The First Anatomical Disquisition on
the Circulation of the Blood,
Addressed to John Riolan, Page 305
A Second Disquisition to John Riolan, in which
Many Objections to the Circulation
of the Blood Are Refuted, Page 313
Anatomical Exercises on the Generation
of Animals, Page 32.9
By William Harvey
Translated by Robert Willis
WILLIAM GILBERT
BIOGRAPHICAL NOTE
WILLIAM GILBERT, 1540-1603
GILBERT was born May 24, 1540, at Colchester
in Essex. He came from an ancient Suffolk fam-
ily and was the eldest of the five sons of Hierome
Gilbert, recorder at Colchester. After complet-
ing his preliminary education at the town
school, Gilbert in 1558 entered St. John's Col-
lege, Cambridge, where he studied for eleven
years. He took his bachelor's degree in 1560,
was elected fellow the following year, and pro-
ceeded to work for his M.A., which he received
in 1564. It was about this time that his interest
in science apparently began to attract notice;
he was appointed mathematical examiner in
1565 and then turned to the study of medicine,
in which he received his doctorate four years
later, when he was also elected senior fellow at
St. John's College.
Shortly after receiving his degree, Gilbert
left Cambridge and apparently made extensive
travels on the continent, particularly in Italy.
It is probable that he received the degree of
Doctor of Physic from a continental univer-
sity, and he presumably then made the acquaint-
ance of some of the| learned men with whom he
was later in correspondence. After his return to
England he settled in London in 1573, where
he practised as a physician with "great success
and applause." Admitted to the College of Phy-
sicians about 1576, Gilbert held the office of
censor from 1581 to 1590; he was treasurer
from 1587 to 1592 and again from 1597 to 1599,
when he succeeded to the presidency of the col-
lege. He served on the committee appointed to
superintend the preparation of the Pharmaco-
poeia LondinenstSy which was undertaken by the
college in 1589 although it did not appear until
1618.
During these years that Gilbert was making
a reputation as a physician, he was also becom-
ing known as a savant in chemistry, physics,
and cosmology. He appears to have studied
these sciences from his youth. He was perhaps
the first advocate of Copernican views in Eng-
land, and he held that the fixed stars were not
all at the same distance from the earth. His
study of navigation is said to have resulted in
the invention of two instruments enabling
sailors "to find out the latitude without seeing
of sun, moon, or stars." But the main basis of
his reputation as a scientist was the publica-
tion in 1600, after eighteen years of reading, ex-
periment, and reflection, of his book on the
magnet, De Magnete Magneticisque Corporibus
et dc Magno Magnete Tellure Physiologia Nova.
It was the first important work in physical
science to be published in England, and almost
immediately after its publication Gilbert was
famous throughout Europe. Kepler paid tribute
to its influence upon his own physical specula-
tions. Galileo first turned his attention to mag-
netism after reading Gilbert and said of him
that he was "great to a degree that is enviable."
Bacon, though he spoke disparagingly of Gil-
bert's attempt "to raise a general system upon
the magnet," praised him as an experimental
philosopher and seems to have taken whole
paragraphs of Gilbert's work as his own.
At his London house, where he possessed a
large collection of books, globes, instruments,
and minerals, Gilbert gathered about him men
who were interested in discussing scientific
problems. The group, which held regular
monthly meetings and constituted a kind of
society, is now looked upon as a precursor of
the Royal Society. Gilbert presumably took a
leading part in these discussions, and he is
known to have continued his scientific investi-
gations, but his only other book, a treatise deal-
ing with meteorological subjects, De Mundo
Nostro Sublunari Philosophia Nova, was edited
after his death by his brother.
In 1 60 1 Gilbert was appointed physician to
Queen Elizabeth, and it appears that he then
moved to the court. Upon the death of the
Queen, it was discovered that her only personal
legacy was made to Gilbert for the prosecu-
tion of his studies. He was immediately reap-
pointed royal physician by James I, but died
shortly afterward, probably of the plague,
on November 30, 1603, and was buried in the
chancel of Holy Trinity church in Colchester.
He bequeathed his scientific library and in-
struments to the College of Physicians, but
they were destroyed in the great fire of London.
x BIOGRAPHICAL NOTE
He left his portrait, which is said to have been hand a globe on which is written the word
painted for that purpose, to Oxford Univer- terrclla; as its inscription the painting has,
sity. In it he is represented as standing, Gilbert, the first investigator of the powers of the
wearing his doctor's robes and holding in his magnet.
CONTENTS
BIOGRAPHICAL NOTE
PREFACE
IX
i
BOOK I
BOOK II
1. Writings of ancient and modern authors con-
cerning the loadstone: various opinions and
delusions 3
2. The loadstone: what it is: its discovery 7 7.
3. The loadstone possesses parts differing in their
natural powers, and has poles conspicuous for 8.
their properties 9
4. Which pole is the north: how the north pole is 9.
distinguished from the south pole 10 10.
5. One loadstone appears to attract another in the 11.
natural position; but in the opposite position 12.
repels it and brings it to rights n 13.
6. The loadstone attracts iron ore as well as the 14.
smelted metal 12
7. What iron is; what its matter: its use 13
8. In what countries and regions iron is produced 16
9. Iron ore attracts iron ore 17 15.
10. Iron ore has and acquires poles, and arranges
itself with reference to the earth's poles 17
11. Wrought-iron, not magnetized by the load- 16.
stone, attracts iron 18
12. A long piece of iron, even not magnetized, as-
sumes a north and south direction 18 17.
13. Smelted iron has in itself fixed north and south
parts, magnetic activity, verticity, and fixed
vertices or poles 19 18.
14. Of other properties of the loadstone and of its
medicinal virtue 19
15. The medicinal power of the iron 20 19.
16. That loadstone and iron ore are the same, and
that iron is obtained from both, like other
metals from their ores; and that all magnetic 20.
properties exist, though weaker, both in smelted
iron and in iron ore 21
17. That the terrestrial globe is magnetic and is a 21.
loadstone; and, just as in our hands the load-
stone possesses all the primary powers (forces)
of the earth, so the earth by reason of the same 22,
potencies lies ever in the same direction in the
universe 23
23,
24.
1. Of magnetic movements 26
2. Of magnetic coition, and, first, of the attrac-
tion exerted by amber, or, more properly, the
attachment of bodies to amber 26
3. Opinions of others concerning magnetic coi-
tion, which they call attraction 34 25
Of the strength of a loadstone and its form: the
cause of coition 36
In what manner the energy inheres in the load-
stone 40
How magnetized iron and smaller loadstones
conform to the terrella, and to the earth itself,
and are governed thereby 42
Of the potency of the magnetic force, and of its
spherical extension 43
Of the geography of the earth and the ter-
rella 43
Of the equinoctial circle of earth and terrella 44
The earth's magnetic meridians 44
Parallels 44
The magnetic horizon 44
Of the magnetic axis and poles 44
Why the coition is stronger at the poles than in
the parts between equator and pole; and the
relative power of coition in different parts of
the earth and the terrella 45
The magnetic force imparted to iron is more
apparent in an iron rod, than in an iron sphere,
or cube, or iron of any other shape 45
That motion is produced by the magnetic force
through solid bodies interposed: of the inter-
position of a plate of iron 45
Of the iron helmet (cap) of the loadstone,
wherewith it is armed at the pole to increase its
energy; efficiency of the same 47
An armed loadstone does not endow with
greater force magnetized iron than does an
unarmed one 47
That unition is stronger with an armed load-
stone: heavier weights are thus lifted: the coi-
tion is not stronger, but commonly weaker 47
That an armed magnet lifts another, and that
one a third: this holds good though there be
less energy in the first 48
That when paper or other medium is inter-
posed, an armed loadstone docs not lift more
than one unarmed 48
That an armed loadstone docs not attract iron
more than an unarmed one; and that the armed
stone is more strongly united to the iron, is
shown by means of an armed loadstone and a
cylinder of polished iron 48
The magnetic force makes motion toward
union, and when united connects firmly 48
That iron within the field of a loadstone hangs
suspended in air, if on account of an obstacle it
cannot come near 49
Intensifying the loadstone's forces 49
Xll
26. Why the love of iron and loadstone appears
greater than that of loadstone and loadstone,
or iron and iron when nigh a loadstone and
within its field 50
27. That the centre of the magnetic forces in the
earth is the centre of the earth; and in the
terrella the terrclla's centre 51
28. That a loadstone does not attract to a fixed
point or pole only, but to every part of a ter-
rella, except the equinoctial circle 51
29. Of difference of forces dependent on quantity
or mass 51
30. The shape and the mass of an iron object are
important in magnetic coitions 52
31. Or oblong and round stones 52
32. Some problems and magnetic experiments on
the coition, and repulsion, and regular move-
ment of magnetic bodies 52
33. Of the difference in the ratio of strength and
movement of coition within the sphere of
influence 54
34. Why a loadstone is of different power in its
poles as well in the north as in the south re-
gions 55
35. Of a perpetual-motion engine actuated by the
attraction of a loadstone, mentioned by
authors 56
36. How a strong loadstone may be recognized 56
37. Uses of the loadstone as it affects iron 57
38. Of the attractions of other bodies 57
39. Of mutually repellent bodies 59
BOOK III
1. Of direction 60
2. Directive (or vcrsorial) force, which we call
verticity: what it is; how it resides in the load-
stone; and how it is acquired when not natu-
rally produced 62
3. How iron acquires verticity from the loadstone,
and how this verticity is lost or altered 64
4. Why magnetized iron takes opposite verticity :
and why iron touched by the true north side of
the stone moves to the earth's north, and when
touched by the true south side to the earth's
south: iron rubbed with the north point of the
stone does not turn to the south, nor vice versa,
as all writers on the loadstone have erroneously
thought 65
5. Of magnetizing stones of different shapes 67
6. What seems to be a contrary movement of
magnetic bodies is the regular tendence to
union 67
7. A determinate verticity and a directive power
make magnetic bodies accord, and not an at-
tractional or a repulsive force, nor strong coi-
tion alone, or unition 67
8. Of disagreements between pieces of iron on the
same pole of a loadstone; how they may come
together and be conjoined 68
9. Directional figures showing the varieties of
rotation 69
10. Of the mutation of verticity and magnetic
WILLIAM GILBERT
properties, or of the alteration of the force
awakened by the loadstone 70
1 1 . Of friction of iron with the mid parts of a load-
stone between the poles, and at the equinoctial
circle of a terrella 71
12. How verticity exists in all smelted iron not
excited by the loadstone 71
13. Why no other bodies save the magnetic are
imbued with verticity by friction with a load-
stone; and why no body not magnetic can im
part and awaken that force 73
14. The position of a loadstone, now above, anon
beneath, a magnetic body suspended in equi-
librium, alters neither the force nor the ver-
ticity of the magnetic body 73
15. The poles, equator, centre, are permanent and
stable in the unbroken loadstone, when it is
reduced in size and a part taken away, they
vary and occupy other positions 74
16. If the south part of a loadstone have a part
broken off, somewhat of power is taken away
from the north part also 74
17. Of the use of rotary needles and their advan-
tages; how the directive iron rotary needles of
sun-dials and the needles of the mariner's com-
pass are to be rubbed with loadstone in order to
acquire stronger verticity 75
BOOK IV
1. Of variation 77
2. That variation is due to inequality among the
earth's elevations 79
3. Variation is constant at a given place 80
4. The arc of variation does not differ according
to distance between places 81
5. An island in ocean docs not alter the variation;
neither do mines of loadstone 81
6. That variation and direction are due to the
controlling force of the earth and the rotatory
magnetic nature, not by an attraction or a coi-
tion or by other occult cause 81
7. Why the variation due to this lateral cause is
not greater than hitherto it has been observed
to be, seldom appearing to amount to two
points of the compass, except near the poles 82
8. Of the construction of the common mariner's
compass, and of the different compasses of
various nations 83
9. Whether terrestrial longitude can be found
from variation 84
1 0. Why in various places near the pole the varia-
tions are much ampler than in lower lati-
tudes 84
1 1 . Cardan's error in seeking to determine the dis-
tance of the earth's centre from the centre of
the world by means of the loadstone (in his
De Propprtionibus, V) 85
12. Of finding the amount of the variation; what
the quantity is of the arc of the horizon from
its arctic or antarctic intersection by a meridian
to the point toward which the needle turns 85
13. Observations made by seamen commonly vary
and are untrustworthy, partly through mistakes
and want of knowledge and the imperfcctness
of the instruments, and partly because the sea
is seldom so calm but shadows or lights may
rest on the instruments 89
14. Of the variation under the equinoctial line and
nearby 89
15. The variation of the magnetized needle in the
great sea, Ethiopic and American, below the
equator 89
16. Of the variation in Nova Zembla 90
17. Variation in the South Sea 90
1 8. Of the variation in the Mediterranean Sea 90
19. The variation in the interior of the great con-
tinents 90
20. The variation in the Eastern Ocean 90
21. How the deviation of the needle is greater or
less according to the distances of places 91
BOOK V
1. Of the dip of the magnetic needle 92
2. Diagram showing dip of the magnetic needle in
different positions of a sphere and horizons of
the earth in which there is no variation of dip 95
3. An instrument for showing by the action of a
loadstone the degree of dip below the horizon
in any latitude. Description of the instru-
ment; its uses 96
4. Of a suitable length of needle on the terrella
for showing the dip 97
5. That dip is not caused by the attraction of a
loadstone but by its power of giving direction
and rotation 97
6. Of the ratio of the dip to latitude and the
causes thereof 98
7. Explanation of the diagram of the rotation of
CONTENTS xiii
magnetized iron 99
8. Diagram of the rotation of magnetized iron
showing the magnetic dip in all latitudes, and
showing the latitude from the rotation and
dip 100
9. Demonstration of direction, or of variation
from the true direction, together with dip,
simply by the movement in water, due to the
power of controlling and rotating 101
10. Of variation of dip 102
11. Of the formal magnetic act spherically ef-
fused 102
12. The magnetic force is animate, or imitates a
soul; in many respects it surpasses the human
soul while that is united to an organic body 104
BOOK VI
1. Of the globe of earth as a great loads tone 106
2. The magnetic axis of the earth remains in-
variable 1 06
3. Of the daily magnetic revolution of the globes,
as against the time-honored opinion of a pri-
mum mobile: a probable hypothesis 107
4. That the earth hath a circular motion in
5. Arguments of those who deny the earth's mo-
tion, and refutation thereof 113
6. Of the cause of the definite time of the total
revolution of the earth 1 16
7. Of the earth's primary magnetic nature whereby
her poles are made different from the poles of
the ecliptic 117
8. Of the precession of the equinoxes by reason of
the magnetic movement of the earth's poles in
the arctic and antarctic circle of the zodiac 1 1 7
9. Of the anomaly of the precession of the equi-
noxes and of the obliquity of the zodiac 1 1 8
On the Loadstone and Magnetic Bodies
and on the Great Magnet the Earth
PREFACE
To THE CANDID READER, STUDIOUS OF THE MAGNETIC PHILOSOPHY
SINCE in the discovery of secret things and in
the investigation of hidden causes, stronger
reasons are obtained from sure experiments
and demonstrated arguments than from prob-
able conjectures and the opinions of philo-
sophical speculators of the common sort;
therefore to the end that the noble substance of
that great loadstone, our common mother (the
earth), still quite unknown, and also the forces
extraordinary and exalted of this globe may the
better be understood, we have decided first to
begin with the common stony and ferruginous
matter, and magnetic bodies, and the parts of
the earth that we may handle and may perceive
with the senses; then to proceed with plain
magnetic experiments, and to penetrate to the
inner parts of the earth. For after we had, in
order to discover the true substance of the
earth, seen and examined very many matters
taken out of lofty mountains, or the depths of
seas, or deepest caverns, or hidden mines, we
gave much attention for a long time to the
study of magnetic forces — wondrous forces
they, surpassing the powers of all other bodies
around us, though the virtues of all things dug
out of the earth were to be brought together.
Nor did we find this our labour vain or fruit-
less, for every day, in our experiments, novel,
unheard-of properties came to light: and our
philosophy became so widened, as a result of
diligent research, that we have attempted to
set forth, according to magnetic principles, the
inner constitution of the globe and its genuine
substance, and in true demonstrations and in
experiments that appeal plainly to the senses, as
though we were pointing with the finger to ex-
hibit to mankind earth, mother of all.
And even as geometry rises from certain
slight and readily understood foundations to
the highest and most difficult demonstrations,
whereby the ingenious mind ascends above the
aether: so does our magnetic doctrine and sci-
ence in due order first show forth certain facts
of less rare occurrence; from these proceed
facts of a more extraordinary kind; at length,
in a sort of series, are revealed things most se-
cret and privy in the earth, and the causes are
recognized of things that, in the ignorance of
those of old or through the heedlessness of the
moderns, were unnoticed or disregarded. But
why should I, in so vast an ocean of books
whereby the minds of the studious are bemud-
dled and vexed — of books of the more stupid
sort whereby the common herd and fellows
without a spark of talent are made intoxicated,
crazy, puffed up; and are led to write numer-
ous books and to profess themselves philoso-
phers, physicians, mathematicians, and astrolo-
gers, the while ignoring and contemning men
of learning — why, I say, should I add aught
further to this confused world of writings, or
why should I submit this noble and (as com-
prising many things before unheard of) this
new and inadmissible philosophy to the judg-
ment of men who have taken oath to follow the
opinions of others, to the most senseless cor-
rupters of the arts, to lettered clowns, gram-
matists, sophists, spouters, and the wrong-
headed rabble, to be denounced, torn to tatters
and heaped with contumely. To you alone, true
philosophers, ingenuous minds, who not only
in books but in things themselves look for
knowledge, have I dedicated these foundations
of magnetic science — a new style of philoso-
phizing. But if any see fit not to agree with the
opinions here expressed and not to accept cer-
tain of my paradoxes, still let them note the
great multitude of experiments and discoveries
— these it is chiefly that cause all philosophy to
flourish; and we have dug them up and dem-
PREFACE
onstrated them with much pains and sleepless
nights and great money expense. Enjoy them
you, and, if ye can, employ them for better pur-
poses. I know how hard it is to impart the air
of newness to what is old, trimness to what is
gone out of fashion; to lighten what is dark; to
make that grateful which excites disgust; to
win belief for things doubtful; but far more
difficult is it to win any standing for or to es-
tablish doctrines that are novel, unheard-of,
and opposed to everybody's opinions. We care
naught, for that, as we have held that philoso-
phy is for the few.
We have set over against our discoveries and
experiments larger and smaller asterisks ac-
cording to their importance and their subtility.
Let whosoever would make the same experi-
ments handle the bodies carefully, skilfully,
and deftly, not heedlessly and bunglingly;
when an experiment fails, let him not in his
ignorance condemn our discoveries, for there
is naught in these books that has not been in-
vestigated and again and again done and re-
peated under our eyes. Many things in our rea-
sonings and our hypotheses will perhaps seem
hard to accept, being at variance with the gen-
eral opinion; but I have no doubt that here-
after they will win authoritativeness from the
demonstrations themselves. Hence the more
advanced one is in the science of the loadstone,
the more trust he has in the hypotheses, and
the greater the progress he makes; nor will one
reach anything like certitude in the magnetic
philosophy, unless all, or at all events most, of
its principles are known to him.
This natural philosophy (physiologid) is al-
most a new thing, unheard of before; a very
few writers have simply published some mea-
gre accounts of certain magnetic forces. There-
fore we do not at all quote the ancients and
the Greeks as our supporters, for neither can
paltry Greek argumentation demonstrate the
truth more subtilly nor Greek terms more ef-
fectively, nor can both elucidate it better. Our
doctrine of the loadstone is contradictory of
most of the principles and axioms of the
Greeks. Nor have we brought into this work
any graces of rhetoric, any verbal ornateness,
but have aimed simply at treating knotty ques-
tions about which little is known in such a
style and in such terms as are needed to make
what is said clearly intelligible. Therefore we
sometimes employ words new and unheard of,
not (as alchemists are wont to do) in order to
veil things with a pedantic terminology and to
make them dark and obscure, but in order that
hidden things with no name and up to this
time unnoticed may be plainly and fully pub-
lished.
After the magnetic experiments and the ac-
count of the homogenic parts of the earth, we
proceed to a consideration of the general na-
ture of the whole earth; and here we decided
to philosophize freely, as freely, as in the past,
the Egyptians, Greeks, and Latins published
their dogmas; for very many of their errors
have been handed down from author to author
till our own time; and as our sciolists still take
their stand on these foundations, they continue
to stray about, so to speak, in perpetual dark-
ness. To those men of early times and, as it
were, first parents of philosophy, to Aristotle,
Theophrastus, Ptolemy, Hippocrates, Galen,
be due honour rendered ever, for from them
has knowledge descended to those that have
come after them: but our age has discovered
and brought to light very many things which
they too, were they among the living, would
cheerfully adopt. Wherefore we have had no
hesitation in setting forth, in hypotheses that
are provable, the things that we have through
a long experience discovered. Farewell.
BOOK FIRST
CHAPTER 1. Writings of ancient and modern
authors concerning the loadstone: various opin-
ions and delusions
IN former times when philosophy, still rude
and uncultured, was involved in the murki-
ness of errors and ignorances, a few of the vir-
tues and properties of things were, it is true,
known and understood: in the world of plants
and herbs all was confusion, mining was un-
developed, and mineralogy neglected. But
when, by the genius and labours of many
workers, certain things needful for man's use
and welfare were brought to light and made
known to others (reason and experience mean-
while adding a larger hope), then did man-
kind begin to search the forests, the plains, the
mountains and precipices, the seas and the
depths of the waters, and the inmost bowels of
earth, and to investigate all things. And by
good luck at last the loadstone was found, as
seems probable, by iron-smelters or by miners
in veins of iron ore. On being treated by the
metallurgists, it quickly exhibited that strong
powerful attraction of iron — no latent nor ob-
scure property, but one easily seen of all: one
observed and commended with many praises.
And after it had come forth as it were out of
darkness and out of deep dungeons and been
honoured of men on account of its strong and
marvellous attraction of iron, then many an-
cient philosophers and physicians discoursed of
it, and briefly (but briefly only) made it matter
of record: as, for instance, Plato in the Ion,
Aristotle only in his first book On the Soul;
likewise Theophrastus the Lesbian, Dioscor-
ides, Caius Plinius Secundus, Julius Solinus.
These record only that the loadstone attracts
iron: its other properties were all hid. But lest
the story of the loadstone should be jejune and
too brief, to this one sole property then known
were appended certain figments and falsehoods
which in the early time no less than nowadays
were by precocious sciolists and copyists dealt
out to mankind to be swallowed. For example,
they asserted that a loadstone rubbed with gar-
lic does not attract iron; nor when it is in pres-
ence of a diamond. The like of this is found in
Pliny and in Ptolemy's Quadripartitum; and
errors have steadily been spread abroad and
been accepted — even as evil and noxious plants
ever have the most luxuriant growth — down to
our day, being propagated in the writings of
many authors who, to the end that their vol-
umes might grow to the desired bulk, do write
and copy all sorts about ever so many things of
which they know naught for certain in the
light of experience. Such fables about the load-
stone even Georgius Agricola, a man that has
deserved well indeed of letters, has inserted as
truthful history in his books DC natura fossil-
ium, putting his trust in others' writings. Ga-
len, in the ninth book of his De simplicium
medicamentorum jacultatibus, recognizes its
medicinal virtue, and its natural power of at-
tracting iron, in the first book of his On the
Natural Faculties; but he knew not the cause,
any more than Dioscorides before him, nor did
he seek further. But his translator Matthiolus
furbishes again the garlic and diamond story,
and further brings in the fable of Mohammed's
shrine having an arched roof of magnets so
that the people might be fooled by the trick of
the coffin suspended in air, as though 'twere
some divine miracle. But this is shown to be
false by the reports of travellers. Pliny, how-
ever, records that the architect Chinocrates be-
gan to put an arched roof of loadstone on the
temple of Arsinoe at Alexandria, so that her
effigy in iron might seem to be suspended in
air: in the meantime the architect died, as also
Ptolemy, who had ordered the work to be done
in honor of his sister.
But little has been written by the ancients
about the causes of the attraction of iron: some
trifling remarks of Lucretius and others are
extant; other authors barely make slight men-
tion of the attraction of iron: all these are be-
rated by Cardan for being so heedless and in-
different about so notable a matter, so broad a
field of philosofftiizing, and for not giving a
fuller account or a more developed philosophy;
yet Cardan himself in his ponderous volumes
has handed down to posterity, beyond a few
commonplaces and quotations from other writ-
WILLIAM GILBERT
crs and false discoveries, naught that is worthy
of a philosopher. Of later authors, some tell
only of its efficacy in medicine, as Antonius
Musa Brasevolus, Baptista Montanus, Amatus
Lusitanus, as did before them Oribasius in
Book XIII of the De jacuhate metallicorum,
Avicenna, Serapio Mauritanus, Abohali (Hali
Abbas), Santes de Ardoniis, Petrus Appon-
ensis, Marcellus, Arnaldus. Only a few points
touching the loadstone are very briefly men-
tioned by Marbodeus Callus, Albertus, Mat-
thaeus Silvaticus, Hermolaus Barbatus, Camil-
lus Leonhardus, Cornelius Agrippa, Fallopius,
Joannes Langius, Cardinal de Cusa, Hannibal
Roserius Calaber: by all these the subject is
handled in the most careless way, while they
repeat only the figments and ravings of others.
Matthiolus compares the attractive virtues of
the loadstone, which pass through iron, to the
mischief of the torpedo, whose poison passes
through bodies and spreads in an occult way.
Gulielmus Puteanus in his Ratio purgantium
medicamentorum discusses the loadstone brief-
ly and crudely. Thomas Erastus, knowing
naught of the nature of the loadstone, draws
from it weak arguments against Paracelsus.
Georgius Agricola, like Encelius and other
writers on metals, simply describes it. Alex-
ander Aphrodiseus, in his Problemata, judges
the question of the loadstone to be incapable of
explication. Lucretius Carus, the Epicurean
poet, deems the attraction to be due to this, that
as there is from all things an efflux of minutest
bodies, so there is from iron efflux of atoms into
the space betwixt the iron and the loadstone —
a space emptied of air by the loadstone's atoms
[seeds] ; and when these begin to return to the
loadstone, the iron follows, the corpuscles be-
ing entangled with each other. Something sim-
ilar is said by Joannes Costaeus, following Plu-
tarch. Thomas Aquinas, in his Physica, Book
VII, treating briefly of the loadstone, gets at
the nature of it fairly well: with his godlike
and perspicacious mind he would have devel-
oped many a point had he been acquainted
with magnetic experiments. Plato holds the
magnetic virtue to be divine.
But when, some three or four hundred years
ago, the magnetic movement to the north and
the south was discovered or recognized anew,
many learned men, each according to his own
gifts, strove to honour witb admiration and
praise or to explain with feeble reasonings a
property so curious and so necessary for the use
of mankind. Of more recent authors, very
many have striven to discover the cause of this
direction and movement to north and south,
and to understand this so great miracle of na-
ture and lay it open to others: but they wasted
oil and labor, because, not being practical in the
research of objects in nature, being acquainted
only with books, being led astray by certain
erroneous physical systems, and having made
no magnetical experiments, they constructed
certain raciocinations on a basis of mere opin-
ions, and old-womanishly dreamt the things
that were not. Marcilius Ficinus chews the cud
of ancient opinions, and to give the reason of
the magnetic direction seeks its cause in the
constellation Ursa: in the loadstone, says he,
the potency of Ursa prevails and hence it is
transferred into the iron. Paracelsus declares
that there are stars which, gifted with the load-
stone's power, do attract to themselves iron.
Levinus Lemnius describes and praises the
mariner's compass, and on certain grounds in-
fers its antiquity: he does not divulge the hid-
den miracle which he makes profession to
know. The people of Amalfi, in the kingdom
of Naples, first, 'tis said, constructed a mar-
iner's compass; and, as Flavius Blondus says,
the townsmen do not without reason boast,
they were so taught by one Joannes Goia, a
fellow-citizen, in the year 1300. This town is in
the Kingdom of Naples, not far from Salerno,
and near the promontory of Minerva. The
sovereignty of the place was conferred by
Charles V on Andrea Doria, the great naval
commander, in recognition of his splendid
achievements. And that nothing ever has been
contrived by the art of man nor anything been
of greater advantage to the human race than
the mariner's compass is certain: but many in-
fer from ancient writings and from certain ar-
guments and conjectures, that the compass was
discovered earlier and received among the arts
of navigation. Knowledge of the mariner's
compass appears to have been brought into
Italy by the Venetian Paolo [Marco Polo],
who about the year 1260 learned the art of the
compass in China; still I do not want to strip
the Amalfitani of so great an honour, seeing
that by them compasses were first commonly
made in Mediterranean lands. Goropius as-
cribes the invention to the Cimbri or Teutons,
on the ground that the thirty-two names of the
winds inscribed on the compass are pro-
jounced in German by all mariners, whether
they be British or Spaniards, or Frenchmen.
But the Italians give them names in their own
vernacular. Some think that Solomon, King of
Judea, was acquainted with the compass and
ON THE LOADSTONE
taught the use of it to his pilots for their long
voyages when they brought from the Western
Indies such a quantity of gold: hence Arias
Montanus holds that the regions in Peru that
abound in gold got their name from the He-
brew word Paruaim. But it is more probable
that the gold came from the coast of lower
Ethiopia, or, as others declare, from the region
called Cephala. The story seems less true for
the reason that the Phoenicians, next neighbours
of Judea, most skilful navigators in early times
(whose talents, labour, and counsels Solomon
employed in building ships and in his expedi-
tions as well as in other ways), were ignorant
of magnetic aids, of the use of the mariner's
compass: for were it used by them, doubtless
the Greeks, the Italians, and all the barbarians
would have known of a thing so necessary and
so celebrated through common use; nor would
things famous, most easily known, and of the
highest necessity ever perish in oblivion; on
the contrary, the knowledge would have been
handed on to posterity, or some memorial in
writing would survive.
Sebastian Cabot first discovered that the
magnetized iron (needle) varied. Gonzales
Oviedo first made mention in his history that
in the meridian of the Azores there is no varia-
tion. Fernel, in his book De abditis rerun*
causis, says that in the loadstone is a hidden
and abstruse cause: elsewhere he says this cause
is celestial, and he does but explain the un-
known by the more unknown. This search af-
ter hidden causes is something ignorant, beg-
garly, and resultless. The ingenious Fracas-
torio, a philosopher of no common stamp, asks
what gives direction to the loadstone [needle],
and imagines the existence of hyperborean
magnetic mountains, attracting objects of mag-
netic iron. This opinion, in some degree ac-
cepted by others also, many authors follow in
their writings, their geographical maps, their
marine charts, and their descriptions of the
globe: dreaming magnetic poles and mighty
cliffs, apart from the earth's poles. Of date two
hundred years or more earlier than Fracastorio
is a small work attributed to one Petrus Pere-
grinus, a pretty erudite book considering the
time: many believe it owes its origin to the
opinions of Roger Bacon, Englishman of Ox-
ford. In this work the arguments touching the
magnetic direction are drawn from the celestial
poles and from the heaven itself. From this
book of Petrus Peregrinus, Joannes Taisner
Hannonius extracted the matter of a little vol-
ume, which he published for new. Cardan
makes much of the star in the tail of Ursa
Major; the cause of variation he assigns to its
rising, thinking that variation is always certain
at the rising of the star. But the difference of
variation for change of locality, and the muta-
tions in many places — mutations that even in
the southern regions are irregular — preclude
this exclusive dominance of one star at its
northern rising. The College of Coimbra seeks
the cause in some region of the heavens nigh to
the pole; Scaliger, in the I3ist of his Exercita-
tiones on Cardan's work De subtilitate, brings
in a celestial cause to himself unknown, and
terrestrial loadstones that have nowhere been
discovered; and seeks the cause not in the
"siderite mountains" but in that force which
formed them, to wit, in the part of the heavens
which overhangs that northern point. This
opinion the learned author dresses in abundant
verbiage and crowns with many subtile obser-
vations in the margin: but his reasons are not
so subtile. Martinus Cortesius holds that the
seat of the attraction is beyond the poles, and
that it is the heavens in motion. One Bessard, a
Frenchman, studies the pole of the Zodiac, but
to as little purpose. Jacobus Severtius, of Paris,
after quoting a few observations of others,
fashions new errors about loadstones of differ-
ent regions being different in direction, as also
about the eastern and western parts of a load-
stone. Robert Norman, an Englishman, posits
a point and place toward which the magnet
looks (but whereto it is) not drawn: toward
which magnetized iron, according to him, is
collimated, but which does not attract it. Fran-
ciscus Maurolycus discusses a few problems re-
garding the loadstone, adopting the current
opinions of others; he believes that the varia-
tion is caused by a certain magnetic island
mentioned by Olaus Magnus. Josephus Costa,
knowing nothing whatever of the subject, nev-
ertheless pours out empty words about the
loadstone. Livio Sanuto, in his Geography
(written in Italian), discourses at length of the
prime magnetic meridian, of the magnetic
poles, whether they are terrestrial or celestial;
treats also of an instrument for finding the
longitude; but as he does not understand the
nature of the loadstone, he does but add errors
and obscurities to his otherwise excellent trea-
tise. Fortunius Affaitatus has some rather silly
philosophizing about attraction of iron and
the turning toward the poles. Very recently
Baptista Porta, a philosopher of no ordinary
note, makes the seventh book of his Magia nat*
uralis a very storehouse and repertory of mag-
6
WILLIAM GILBERT
netic wonders; but he knows little about the
movements of the loadstone, and never has
seen much of them; much of what he has
learned about its obvious properties, either
from Messer Paolo, the Venetian, or through
his own studies, is not very accurately noted
and observed; the book is full of most errone-
ous experiments, as will appear in fitting place;
still I hold him worthy of praise for that he
essayed so great a task (even as he has essayed
many another task, and successfully too, and
with no inconsiderable results), and that he
has given occasion for further researches.
All these philosophers, our predecessors, dis-
coursing of attraction on the basis of a few
vague and indecisive experiments and of rea-
sonings from the recondite causes of things;
and reckoning among the causes of the direc-
tion of the magnet, a region of the sky, celestial
poles, stars, asterisms; or mountains, cliffs, va-
cant space, atoms, attractional or collimational
regions beyond the heavens, and other like un-
proved paradoxes, are world-wide astray from
the truth and are blindly wandering. But we do
not propose just now to overturn with argu-
ments either these their errors and impotent
reasonings, or the other many fables about the
loadstone, or the fairy-tales of mountebanks
and story-tellers; as, for example, the questions
raised by Franciscus Rueus about the load-
stone, whether it is an imposture of cacodae-
mons; or the assertion that a loadstone placed
unawares under the head of a sleeping woman
drives her out of the bed if she be an adulteress;
or that by its fume and vapour the loadstone is
of use to thieves, as though the stone were by
nature given to promote thefts; or that it with-
draws bolts and opens locks, as Serapio insane-
ly imagines; or that iron held by a loadstone's
attraction, being placed in a balance, adds
nought to the weight of the loadstone, as
though the weight of the iron were absorbed by
the virtue of the loadstone; or that, as Serapio
and the Moors report, there are in Indian seas
certain sharp-pointed rocks abounding in load-
stone, the which draw every nail out of ships
that land alongside them and hold the vessels:
this story, Olaus Magnus does not fail to recite:
he tells of mountains in the North possessing
such power of attraction that ships have to be
constructed with wooden pegs, so that as they
sail by the magnetic cliffs there be no iron
nails to draw out.
Nor will we take the trouble to refute such
stories as that a white loadstone may be used
as a philter; or that, as Abohali (Hali Abbas)
rashly asserts, when held in the hand it cures
pains of the feet and cramps; or that, as Pictor-
ius sings, it gives one favour and acceptance
with princes or makes one eloquent; that, as
Albertus Magnus says, there are two species of
loadstones, one pointing north, the other south;
or that iron is directed toward the northern
stars by a force communicated from the polar
stars, even as plants, like the sunflower, follow
the sun; or, as the astrologer Lucas Gauricus
held, that beneath the tail of Ursa Major is a
loadstone; Lucas further assigns the loadstone
(as the sardonyx and the onyx) to the planet
Saturn, but also to Mars (with the diamond,
jasper, and ruby), so that the loadstone, accord-
ing to him, is ruled by two planets; further,
Lucas says that the loadstone belongs to the
sign Virgo; and with a veil of mathematical
erudition does he cover many similar disgrace-
ful stupidities. Gaudentius Merula advises that
on a loadstone be graven the image of a bear,
when the moon looks to the north, so that be-
ing suspended by an iron thread it may win
the virtue of the celestial Bear; Ficinus writes,
and Merula copies, that the loadstone draws
iron and makes it point north, because it is of
higher order than iron in the Bear. Others tell
that in daytime the loadstone possesses the
power of attracting iron, but that at night this
power is feeble or rather null; Ruellius writes
that the loadstone's force, when failing or
dulled, is restored by the blood of a buck; it
has been said that a buck's blood frees the mag-
net from the diamond's sorcery, giving back its
lost power when the magnet is bathed in the
blood — this, because of the variance between
that blood and the diamond; Arnoldus de Vil-
lanova fancies that the loadstone frees women
from witchcraft and puts demons to flight;
Marbodaeus, a Frenchman, fugleman of vain
imaginings, says that it can make husbands
agreeable to wives and may restore wives to
their husbands; Caelius Calcagninius in his
Relationes says that a magnet pickled with salt
of the sucking-fish has the power of picking
up a piece of gold from the bottom of the deep-
est well. In such-like follies and fables do phil-
osophers of the vulgar sort take delight; with
such-like do they cram readers a-hungered for
things abstruse, and every ignorant gaper for
nonsense. But when the nature of the loadstone
shall have been in the discourse following dis-
closed, and shall have been by our labours and
experiments tested, then will the hidden and
recondite but real causes of this great effect
be brought forward, proven, shown, demon-
ON THE LOADSTONE
strated; then, too, will all darkness vanish;
every smallest root of error, being plucked up,
will be cast away and will be neglected; and
the foundations of a grand magnetic science
being laid will appear anew, so that high intel-
lects may no more be deluded by vain opin-
ions.
There are other learned men who on long
sea voyages have observed the differences of
magnetic variation; as that most accomplished
scholar Thomas Hariot, Robert Hues, Edward
Wright, Abraham Kendall, all Englishmen;
others have invented and published magnetic
instruments and ready methods of observing,
necessary for mariners and those who make
long voyages: as William Borough in his little
work the Variation of the Compass, William
Barlo [Barlowe] in his Supplement, Robert
Norman in his New Attractive — the same Rob-
ert Norman, skilled navigator and ingenious
artificer, who first discovered the dip of the
magnetic needle. Many others I pass by of
purpose: Frenchmen, Germans, and Spaniards
of recent time who in their writings, mostly
composed in their vernacular languages, either
misuse the teachings of others, and like fur-
bishers send forth ancient things dressed with
new names and tricked in an apparel of new
words as in prostitutes' finery; or who publish
things not even worthy of record ; who, pilfer-
ing some book, grasp for themselves from other
authors, and go a-begging for some patron, or
go a-fishing among the inexperienced and the
young for a reputation; who seem to trans-
mit from hand to hand, as it were, erroneous
teachings in every science and out of their
own store now and again to add somewhat
of error.
CHAPTER 2. The Loadstone: what it is:
its discovery
THIS stone is commonly called magnet, either
after its finder {not Pliny's mythical herdsman
— copied from Nicander — the hobnails of
whose brogues and the point of whose staff
were held fast in a magnetic region while he
was pasturing his cattle), or after the district
Magnesia in Macedonia, abounding in load-
stones; or after the City of Magnesia in Ionia
of Asia Minor, on the river Maender; hence
Lucretius writes, "Quern Magneta vacant pat-
rio de nomine Graii, Magnetum quia sit patriis
in montibus ortus.1" It is called heradeus from
1 Which the Greeks call magnetes, from the name
of its country, for it had its origin in the native hills
of the Magnesians.
the city Heraclea, or after that unconquerable
hero Hercules, because of its great strength and
its power and dominion over iron which is the
subduer of all things; it is also called sidcritis,
as though one should say ferrarius (ffrrarius
lapis — ironstone). It was not unknown to the
earliest writers, whether among the Greeks, as
Hippocrates and others, or (as I believe)
among the Jews and the Egyptians; for in the
most ancient iron mines, in particular the most
famous mines of Asia, the loadstone, brother
uterine of iron, was oft dug out in company
with that ore. And if those things be true
which are told about the people of China,
neither were they in primitive times ignorant
of magnetic experiments, for even in their
country are seen the most excellent magnets in
the world. The Egyptians, as Manetho relates,
give it the name of "the bone of Horus," call-
ing the potency that presides over the revolu-
tion of the sun Horus, as the Greeks called it
Apollo. But later, as Plato declares, Euripides
gave to it the name magnet. It is mentioned
and praised by Plato in the Ion, by Nicander of
Colophon, Theophrastus, Dioscorides, Pliny,
Solinus, Ptolemy, Galen, and other investiga-
tors of nature. But considering the great differ-
ences of loadstones, their dissimilitude in hard-
ness, softness, heaviness, lightness, density,
firmness, friableness: in colour and in all other
qualities; these writers have not handed down
any sufficient account of it. The history of the
magnet was overlooked by them, or, if written,
was incompletely given, because in olden time
objects of many kinds and foreign products
never before seen were not brought in by trad-
ers and mariners as they are wont to be brought
in now, when all manner of commodities —
stones, woods, spices, herbs, metals, and metal-
lic wares — are eagerly sought for all over the
earth; neither was mining carried on every-
where in early times as it is now.
The difference between loadstones rests on
their respective power: hence one loadstone is
male, another female: so the ancients were wont
to distinguish many objects of the same species.
Pliny quotes from Sotacus five kinds, viz.: the
loadstones of Ethiopia, Macedonia, Boeotia,
Troas, and Asia, respectively, which were the
chief sorts known to the ancients. But we rec-
ognize as many kinds as there are in the whole
world regions differing in soil; for in every
clime, in every province, in all kinds of land,
either the loadstone is found or lies unknown
because of its deep site or its inaccessible situa-
tion; or, because of its weaker and less potent
8
WILLIAM GILBERT
virtues, it is not recognized by us the while we
see it and touch it.
For the ancients, the differences were based
on the colour: The magnets from Magnesia in
Macedonia were red and black, those from
Boeotia red rather than black, those from the
Troad black without strength, those from Asi-
an Magnesia white, without power of attract-
ing iron, and resembling pumice. A strong
loadstone and one that under experiment dem-
onstrates its power nowadays generally re-
sembles unpolished iron and usually is found
in iron mines: sometimes it is found also form-
ing a continuous vein by itself: such load-
stones are imported from the East Indies,
China, and Bengal, and they are of the colour
of iron, or of a dark blood-red or liver colour.
These are the most excellent and often are of
great size and weight, as if broken off a great
rock; or again they are as if complete in them-
selves. Some of these, though they may weigh
but one pound, will lift four ounces, or half a
pound, or even an entire pound of iron. In
Arabia are found red loadstones shaped like
tiles, not as heavy as those imported from
China, yet strong and good. Rather black load-
stones are found in Elba, an island of the
Etrurian sea; with these occur also white load-
stones like those from the mines of Caravaca in
Spain: but they are of inferior strength. Black
loadstones also are found, and these, too, are
rather inferior in strength, for example, those
met with in the iron mines of Norway and in
the coast region along the Cattegat. Blue-black
and dusky-blue loadstones are likewise power-
ful and highly prized. But there are others of a
lead colour, fissile or not fissile, that can be split
up like slate; I have also loadstones resembling
an ashy-gray marble, mottled like gray marble:
these take a high polish. In Germany are load-
stones perforated like the honeycomb; these are
lighter than the other sorts, yet they are power-
ful. The metallic loadstones are those which
are smelted into the best of iron; the rest are
not easily smelted, but are burnt.
There are loadstones that are very heavy, as
there are others very light; some are very pow-
erful and carry masses of iron; others are
weaker and less powerful; some so faint and
void of strength that they can hardly attract
ever so small a piece of iron, nor do they repel
an opposite magnetized body. Others are firm
and tough, nor are they easy to work; others
are friable. Again, some are dense and hard
like corundum, or light or soft like pumice;
porous or solid; smooth and uniform, or irreg-
ular and corroded. Now hard as iron, nay
sometimes harder to cut or to file than iron;
again as soft as clay. Not all magnets can prop-
erly be called stones: some there are that repre-
sent rather rocks; others are rather metallic
ores; others are like clods of earth. So do they
vary and differ from one another, and some
possess more, others less, of the peculiar mag-
netic virtue. For they differ according to the
nature of the soil, and the different mixtures of
clays and humours; according to the lay of the
land and the decay of this highest substance
born to earth: decay due to the concurrence of
many causes and the never-ceasing vicissitude
of rise and decline and the mutations of bodies.
Nor is this stone, endowed as it is with such
power, a rarity: there is no country wherein it
may not be found in one form or other. But
were men to seek it more diligently and at
greater expense, and could they in the face of
difficulties mine it, it might be obtained every-
where, as later we will prove. In many regions
are found and are now opened mines of power-
ful loadstones unknown to ancient authors, in
Germany, for example, where none of them
ever said that loadstones were mined; and yet
since the time within the memory of our fa-
thers when the business of mining began there
to be developed, in many parts of Germany
powerful loadstones of great virtues have been
taken out of the earth, as in the Black Forest
near Helceburg: in Mt. Misena not far from
Schwarzberg; some of considerable strength
from the region betwixt Schneeberg and Anna-
berg in the Joachimsthal, as was observed by
Cordus; also near Pela in Franconia; in Bo-
hemia from the iron mines near Lesse; and in
other places, as we are informed by Georgius
Agricola and other men learned in the art of
mining.
The like is to be said of other countries in
our time; for this stone, famous for its virtues,
as to-day it is well known throughout the
world, so is produced in every land; it is, so to
speak, a native of all countries. In East India,
in China, in Bengal, along the banks of the In-
dus, it is plentiful, also in certain marine rocks;
in Persia, too, in Arabia and the isles of the Red
Sea; in many parts of Ethiopia, as was an-
ciently Zimiri, mentioned by Pliny; in Asia
Minor around Alexandria, Boeotia, Italy, the
island Elba, Barbary; in Spain, still in many
localities as of old; in England quite recently a
vast quantity was found in a mine owned by
a gentleman, named Adrian Gilbert, as also in
Devonshire and in the Forest of Dean; in Ire-
ON THE LOADSTONE
land too, in Norway, Denmark, Sweden, Lap-
land, Livonia, Prussia, Poland, Hungary. For
albeit the terrestrial globe, various humours
and diversities of soils being produced by the
perpetual vicissitude of generaton and decay, is
ever to a greater and greater depth beneath the
surface in the lapse of ages efflorescing, and is
being clothed as it were with a diversified and
perishable covering and wrappage; still from
its interior arises in many places a progeny
nigher to the more perfect body, and makes its
way into the sunlit air. But the weak loadstones
and those of less strength, which thus have
been deprived of their virtue by being soaked
with humours, are visible everywhere, in every
country-side; great masses of these are to be
found in every quarter, without tunnelling
mountains or sinking mines, and without any
of the toils and difficulties of mining, as we will
show in the sequel. These we will so manipu-
late according to a simple process that their
languid and dormant properties shall be made
manifest.
The magnet is called by the Greeks 'rypd/c-
Xeios, as by Theophrastus, and jua^f/ris and
payv^s, as by Euripides, quoted by Plato in
the Ion; by Orpheus it is called alsojucryrrjoo-a
and aidrjpLrrjs (quasi ironstone); by the Latins
it is called magnes Herculeus; by the French
aimant, a corruption of adamas; by the Span-
iards piedramant; by the Italians calamita; by
the English loadstone and adamant stone; by
the Germans magnes s and siegelstein. Among
the English, French, and Spaniards, it has its
common name from adamas, and this is prob-
ably because at some time those people were
led astray by the term siderites, which was ap-
plied both to the diamond and the magnet. The
magnet is called crtSryptr^s because of its prop-
erty of attracting iron; and the diamond is
called (rt,brjplrr)s from the glistening of polished
iron. Aristotle merely names the loadstone in
his work On the Soul, I. f 405a 19] : "
OaXi/s ££ &v aTronveiJiovtbovGl, KLVTITLKOV ri
^vxyv liro\aiJ,@av€LV, hirep rbv
%<fa %xew, or i rov aid^pdv jam. (Thales, too,
seems, from what they relate, to regard the
soul as somewhat producing motion, for he
said that this stone has a soul, since it moves
iron.) The name magnet is also given to an-
other stone differing widely from the siderites,
and having the look of silver: in its nature this
stone resembles amianth (asbestus), and in
form differs from that inasmuch as it consists,
like mica, of laminae; the Germans call it
Katzensilber and
CHAPTER 3. The loadstone possesses parts dif-
fering in their natural powers, and has poles
conspicuous for their properties
THE many qualities exhibited by the loadstone
itself, qualities hitherto recognized yet not well
investigated, are to be pointed out in the first
place, to the end the student may understand
the powers of the loadstone and of iron, and
not be confused through want of knowledge at
the threshold of the arguments and demon-
strations. In the heavens, astronomers give to
each moving sphere two poles; thus do we find
two natural poles of excelling importance even
in our terrestrial globe, constant points related
to the movement of its daily revolution, to wit,
one pole pointing to Arctos (Ursa) and the
north; the other looking toward the opposite
part of the heavens. In like manner, the load-
stone has from nature its two poles, a northern
and a southern; fixed, definite points in the
stone, which are the primary termini of the
movements and effects, and the limits and reg-
ulators of the several actions and properties. It
is to be understood, however, that not from a
mathematical point does the force of the stone
emanate, but from the parts themselves; and
all these parts in the whole — while they belong
to the whole — the nearer they are to the poles
of the stone the stronger virtues do they ac-
quire and pour out on other bodies. These
poles look toward the poles of the earth, and
move toward them, and are subject to them.
The magnetic poles may be found in every
loadstone, whether strong and powerful (male,
as the term was in antiquity) or faint, weak,
and female; whether its shape is due to design
or to chance, and whether it be long, or flat, or
four-square, or three-cornered, or polished;
whether it be rough, broken-off, or unpolished:
the loadstone ever has and ever shows its poles.
But inasmuch as the spherical form, which,
too, is the most perfect, agrees best with the
earth, which is a globe, and also is the form
best suited for experimental uses, therefore we
propose to give our principal demonstrations
with the aid of a globe-shaped loadstone, as be-
ing the best and the most fitting. Take then a
strong loadstone, solid, of convenient size, uni-
form, hard, without flaw; on a lathe, such as is
used in turning crystals and some precious
stones, or on any like instrument (as the nature
and toughness of the stone may require, for
often it is worked only with difficulty), give
the loadstone the form of a ball. The stone thus
prepared is 'a true homogeneous offspring of
the earth and is of the same shape, having got
10
from art the orbicular form that nature in the
beginning gave to the earth, the common
mother; and it is a natural little body endowed
with a multitude of properties whereby many
abstruse and unheeded truths of philosophy,
hid in deplorable darkness, may be more read-
ily brought to the knowledge of mankind. To
this round stone we give the name ^Kpbyr\
[microge] or terrella [earthkin, little earth].
To find, then, poles answering to the earth's
poles, take in your hand the round stone, and
lay on it a needle or a piece of iron wire: the
ends of the wire move round their middle
point, and suddenly come to a standstill. Now,
with ochre or with chalk, mark where the wire
lies still and sticks. Then move the middle or
centre of the wire to another spot, and so to a
third and a fourth, always marking the stone
along the length of the wire where it stands
still: the lines so marked will exhibit meridian
circles, or circles like meridians on the stone or
terrella; and manifestly they will all come to-
gether at the poles of the stone. The circles be-
ing continued in this way, the poles appear,
both the north and the south, and betwixt
these, midway, we may draw a large circle for
an equator, as is done by the astronomer in the
heavens and on his spheres and by the geogra-
pher on the terrestrial globe; for the line so
drawn on this our terrella is also of much
utility in our demonstrations and our magnetic
experiments. Poles are also found in the round
stone, in a versorium, in a piece of iron touched
WILLIAM GILBERT
with a loadstone and resting on a needle or
point (attached at its base to the terrella), so
that it can freely revolve, as in the figure.
On top of the stone AB is set the versorium
in such a way that its pointer may remain in
equilibrium: mark with chalk the direction of
the pointer when at rest. Then move the in-
strument to another spot and again mark the
direction in which the pointer looks; repeat
this many times at many different points and
you will, from the convergence of the lines of
direction, find one pole at the point A, the
other at B. A pointer also indicates the true
pole if brought near to the stone, for it eagerly
faces the stone at right angles, and seeks the
pole itself direct and turns on its axis in a right
line toward the centre of the stone. Thus the
pointer D regards A and F, the pole and the
centre, but the pointer E looks not straight
either toward the pole A or the centre F. A bit
of fine iron wire as long as a barley-corn is
laid on the stone and is moved over the zones
and the surface of the stone till it stands per-
pendicularly erect; for at the poles, whether
N. or S., it stands erect; but the farther it is
from the poles (towards the equator) the more
it inclines. The poles thus found, you are to
mark with a sharp file or a gimlet.
CHAPTER 4. Which pole is the north: how the
north pole is distinguished from the south pole
ONE of the earth's poles is turned toward Cyno-
sura and steadily regards a fixed point in the
heavens (save that it is unmoved by the preces-
sion of the fixed stars in longitude, which
movement we recognize in the earth, as we
shall later show); the other pole is turned
toward the opposite aspect of the heavens, an
aspect unknown to the ancients, but which is
adorned with a multitude of stars, and is itself
a striking spectacle for those who make long
voyages. So, too, the loadstone possesses the
virtue and power of directing itself toward the
north and the south (the earth itself co-operat-
ing and giving to it that power) according to
the conformation of nature, which adjusts the
movements of the stone to its true locations.
In this manner it is demonstrated: put the
magnetic stone (after you have found the
poles) in a round wooden vessel — a bowl or a
dish; then put the vessel holding the magnet
(like a boat with a sailor in it) in a tub of
water or a cistern where it may float freely in
the middle without touching the rim, and
where the air is not stirred by winds (currents)
which might interfere with the natural move-
ment of the stone: there the stone, as if in a
boat floating in the middle of an unruffled sur-
face of still water, will straightway set itself,
and the vessel containing it in motion, and will
turn in a circle till its south pole shall face
north and its north pole, south. For, from a
contrary position, it returns to the poles; and
though with its first too strong impetus it
passes beyond, still, as it comes back again and
ON THE LOADSTONE
n
again, at last it rests at the poles or in the
meridian (save that, according to the place, it
diverges a very little from those points, or from
the meridional line, the cause of which we will
define later). As often as you move it out of
its place, so often, by reason of the extraordi-
nary power with which nature has endowed it,
does it seek again its fixed and determinate
points. Nor does this occur only when the poles
of the loadstone in the float are made to lie
evenly in the plane of the horizon; it takes
place also even though one pole, whether north
or south, be raised or depressed 10, 20, 30, 40,
or 80 degrees from the plane of the horizon;
you shall see the north part of the stone seek
the south, and the south part the north; so
that if the pole of the stone be but one degree
from the zenith and the centre of the heavens,
the whole stone revolves until the pole finds its
own place; and though the pole does not point
exactly to its seat, yet it will incline toward it,
and will come to rest in the meridian of its
true direction. And it moves with the same im-
petus whether the north pole be directed
toward the upper heavens, or whether the
south pole be raised above the horizon. Yet it
must always be borne in mind that though
there are manifold differences between stones,
and one far surpasses another in virtue and
efficiency, still all loadstones have the same lim-
its and turn to the same points. Further, it is
to be remembered that all who hitherto have
written about the poles of the loadstone, all in-
strument-makers, and navigators, are egregi-
ously mistaken in taking for the north pole of
the loadstone the part of the stone that inclines
to the north, and for the south pole the part
that looks to the south: this we will hereafter
prove to be an error. So ill-cultivated is the
whole philosophy of the magnet still, even as
regards its elementary principles.
CHAPTER 5. One loadstone appears to attract
another in the natural position; but in the op-
posite position repels it and brings it to rights
FIRST we have to describe in popular language
the potent and familiar properties of the stone;
afterward, very many subtile properties, as yet
recondite and unknown, being involved in ob-
scurities, are to be unfolded; and the causes of
all these (nature's secrets being unlocked) are
in their place to be demonstrated in fitting
words and with the aid of apparatus. The fact
is trite and familiar, that the loadstone attracts
iron; in the same way, too, one loadstone at-
tracts another. Take the stone on which you
have designated the poles, N. and S.f and put
it in its vessel so that it may float; let the poles
lie just in the plane of the horizon, or at least
in a plane not very oblique to it; take in your
hand another stone the poles of which are also
known, and hold it so that its south pole shall
lie toward the north pole of the floating stone,
and near it alongside; the floating loadstone
will straightway follow the other (provided it
be within the range and dominion of its pow-
ers), nor does it cease to move nor does it quit
the other till it clings to it, unless, by moving
your hand away, you manage skilfully to pre-
vent the conjunction. In like manner, if you
oppose the north pole of the stone in your hand
to the south pole of the floating one, they come
together and follow each other. For opposite
poles attract opposite poles. But, now, if in the
same way you present N. to N. or S. to S., one
stone repels the other; and as though a helms-
man were bearing on the rudder it is off like a
vessel making all sail, nor stands nor stays as
long as the other stone pursues. One stone also
will range the other, turn the other around,
bring it to right about and make it come to
agreement with itself. But when the two come
together and are conjoined in nature's order,
they cohere firmly. For example, if you present
the north pole of the stone in your hand to the
Tropic of Capricorn (for so we may distin-
guish with mathematical circles the round
stone, or terrella, just as we do the globe itself)
or to any point between the equator and the
south pole: immediately the floating stone
turns round and so places itself that its south
pole touches the north pole of the other and is
most closely joined to it. In the same way you
will get like effect at the other side of the equa-
tor by presenting pole to pole; and thus by art
and contrivance we exhibit attraction and re-
pulsion, and motion in a circle toward the con-
cordant position, and the same movements to
12
avoid hostile meetings. Furthermore, in one
same stone we are thus able to demonstrate all
this: but also we are able to show how the self-
same part of one stone may by division become
either north or south. Take the oblong stone ad
in which a is the north pole and d the south.
Cut the stone in two equal parts, and put part
a in a vessel and let it float in water.
You will find that a, the north point, will
turn to the south as before; and in like manner
the point d will move to the north, in the di-
vided stone, as before division. But b and c,
before connected, now separated from each
other, are not what they were before: b is now
south while c is north, b attracts c, longing
for union and for restoration of the original
continuity. They are two stones made out of
one, and on that account the c of one turning
toward the b of the other, they are mutually
attracted, and, being freed from all impedi-
ments and from their own weight, borne as
they are on the surface of the water, they come
together and into conjunction. But if you bring
the part or point a up to c of the other, they
repel one another and turn away; for by such a
position of the parts nature is crossed and the
form of the stone is perverted: but nature ob-
serves strictly the laws it has imposed upon
bodies: hence the flight of one part from the
undue position of the other, and hence the dis-
cord unless everything is arranged exactly ac-
cording to nature. And nature will not suffer
an unjust and inequitable peace, or an unjust
and inequitable peace and agreement, but
makes war and employs force to make bodies
acquiesce fairly and justly. Hence, when right-
ly arranged, the parts attract each other, i.e.,
both stones, the weaker and the stronger, come
together and with all their might tend to
union: a fact manifest in all loadstones, and
not, as Pliny supposed, only in those from Ethi-
opia. The Ethiopic stones if strong, and those
brought from China, which are all powerful
stones, show the effect most quickly and most
plainly, attract with most force in the parts
nighest the pole, and keep turning till pole
looks straight on pole.
The pole of a stone has strongest attraction
for that part of another stone which answers to
it (the adverse, as it is called); e.g., the north
pole of one has strongest attraction for, has the
most vigorous pull on, the south part of an-
other: so too it attracts iron more powerfully,
and iron clings to it more firmly, whether pre-
viously magnetized or not. Thus it has been
settled by nature, not without reason, that the
WILLIAM GILBERT
parts nigher the pole shall have the greatest
attractive force; and that in the pole itself shall
be the seat, the throne as it were, of a high and
splendid power; and that magnetic bodies
brought near thereto shall be attracted most
powerfully and relinquished with most reluc-
tance. So, too, the poles are readiest to spurn
and drive away what is presented to them
amiss, and what is inconformable and foreign.
CHAPTER 6. The loadstone attracts iron ore
as well as the smelted metal
THE most potent virtue of the loadstone and
the one valued by the ancients is the attraction
for iron; for Plato mentions that the magnet,
so called by Euripides, draws to itself iron, and
not only attracts iron rings but also endows
them with the power of doing as the stone it-
self, to wit, of attracting other rings, and that
thus sometimes a long chain of iron objects, as
nails, or rings, is made, the several parts hang-
ing from one another. The best iron (such as
that which from its uses is called odes, and
from the country of the Chalybes, chalybs) is
most readily and strongly attracted by a good
magnet1; but inferior iron, iron that is im-
pure, rusty, not well purged of dross, and not
worked over in the second furnace is attracted
more weakly; and any iron is more faintly at-
tracted if covered and smeared with thick,
greasy, tenacious fluids. The loadstone also at-
tracts iron ores — rich ores and those of the col-
our of iron; poor ores and those without much
pure metal it does not attract unless they re-
ceive special treatment. The loadstone loses
some part of its attractive power, and, as it
were, enters on the decline of old age, if it be
too long exposed in open air and not kept in a
case, with a covering of iron filings or iron
scales: hence it must be packed in such ma-
terial. Nothing withstands this unimpairable
virtue, except what destroys the form of the
body or corrodes it; no, not a thousand adam-
ants made into one. Nor do I believe in the
theamedes, or that it has a power the opposite
of the loadstone's, albeit Pliny, that eminent
author and best of compilers (for he has
handed down to posterity the observations and
discoveries of others and not always or mainly
his own), copies out of other writers the thea-
medes fable, now from repetition become a
familiar story among the moderns. The story
is that in India are two mountains near the
river Indus, and that one of them — consisting
1 See Aristotle's reference to the iron of the Chaly-
bes. See Book i, Chap. 8, p. 15, below.
ON THE LOADSTONE
of loadstone — possesses the power of holding
everything containing iron; while the other,
consisting of theamcdes, repels the same.
Hence if you should have iron nails in the soles
of your shoes, it would be impossible to lift
your foot if you were standing on one of the
mountains, and impossible to stand on the
other at all. Albertus Magnus writes that in his
time a loadstone was found that on one side
drew iron to itself and on the other side re-
pelled it. But Albertus's observation was faulty,
for every loadstone attracts on one side mag-
netized iron, on the other repels, and attracts
magnetized iron more powerfully than non-
magnetized.
CHAPTER 7. What iron is; what its matter;
its use
HAVING declared the origin and nature of the
loadstone, we hold it needful first to give the
history of iron also, and to point out properties
of iron as yet not known, before we come to
the explication of difficulties connected with
the loadstone, and to the demonstrations; be-
fore we come to the consideration of its uniting
and according with iron. Iron is, by all, classed
among metals; it is of bluish colour, very hard,
grows red hot before fusion, is very hard to
fuse, spreads under the hammer, and is reso-
nant. Chemists say that, if fixed earthy sulphur
be combined with fixed earthy mercury and
these two bodies present not a pure white but
a bluish-white colour, if the sulphur prevail,
iron results. For those hard masters of the met-
als, who in many various processes put them
to the torture, by crushing, calcining, smelting,
subliming, precipitating, distinguish this, on
account both of the earthy sulphur and the
earthy mercury, as more truly the child of
earth than any other metal; for neither gold,
nor silver, nor lead, nor tin, nor even copper do
they hold to be so earthy; and therefore it is
treated only in the hottest furnaces with the
help of bellows; and when thus smelted if it
becomes hard again it cannot be smelted once
more without great labour; and its slag can be
fused only with the utmost difficulty. It is the
hardest of metals, subduing and breaking
them all, because of the strong concretion of
the more earthy substance.
Hence we shall better understand what iron
is when we shall have developed, in a way dif-
ferent from that of those who have gone before
us, what are the causes and the matter of met-
als. Aristotle supposes their matter to be an ex-
halation. The chemists in chorus (unison)
declare that sulphur and quicksilver are the
prime elements. Gilgil, the Mauretanian, holds
the prime element to be ash moistened with
water; Georgius Agricola, a mixture of water
with earth; and his opinion differs nought
from Gilgil's thesis. But our opinion is that
metals have their origin and do effloresce in the
uppermost parts of the globe, each distinct by
its form, as do many other minerals and all the
bodies around us. The globe of the earth is not
made of ash or of inert dust. Nor is fresh water
an element, but only a less complex consistence
of the earth's evaporated fluids. Unctuous bod-
ies (pinguia corpora), fresh water void of prop-
erties, quicksilver, sulphur: these are not the
principles of the metals: they are results of an-
other natural process; nor have they a place
now or have they had ever, in the process of
producing metals. The earth gives forth sundry
humours, not produced from water nor from
dry earth, nor from mixtures of these, but from
the matter of the earth itself: these are not dis-
tinguished by opposite qualities or substances.
Nor is the earth a simple substance, as the
Peripatetics imagine. The humours come from
sublimed vapours that have their origin in the
bowels of the earth.
And all waters are extractions from the earth
and exudations, as it were. Therefore Aristotle
is partly in the right when he says that the ex-
halation which condenses in the earth's veins is
the prime matter of metals: for exhalations are
condensed in situations less warm than the
place of their origin, and owing to the structure
of lands and mountains, they are in due time
condensed, as it were in wombs, and changed
into metals. But they do not of themselves
alone constitute the veins of ore; only they
flow into and coalesce with solider matter and
form metals.
When, therefore, this concreted matter has
settled in more temperate cavities, in these
moderately warm spaces it takes shape, just as
in the warm uterus the seed or the embryo
grows. Sometimes the exhalation coalesces only
with matter homogeneous throughout, and
hence some metals are now and then but not
often obtained pure and not needing to be
smelted. But other exhalations, being mixed
with foreign earths, must be smelted; and thus
are treated the ores of all metals, which are
freed from all their dross by the action of fire;
when smelted into the metallic state they are
fluid and then are freed from earthly impur-
ities but not from the true substance of the
earth. But that there is gold, or silver, or cop-
WILLIAM GILBERT
per, or that any other metals exist, does not
happen from any quantitas or proportion of
matter nor by any specific virtues of matter, as
the chemists fondly imagine; but it happens
when, earth cavities and the conformation of
the ground concurring with the fit matter,
those metals take from universal nature the
forms by which they are perfected, just as in
the case of all other minerals, all plants and all
animals: else the kinds of metals would be
vague and undefined; in fact, the varieties are
very few, hardly ten in number.
But why nature should be so grudging in
the number of metals, or why there should be
even so many metals as are recognized by man,
were not easy to explain, though simpletons
and raving astrologers refer to the several
planets their respective metals. But neither do
the planets agree with the metals nor the met-
als with the planets, either in number or in
properties. For what is common between Mars
and iron, save that, like many other imple-
ments, swords and artillery are made of iron?
What has copper to do with Venus? Or how
does tin, or zinc, relate to Jupiter? These were
better dedicated to Venus. But a truce to old
wives' talk. Thus exhalations are the remote
cause of the generation of metals; the proxi-
mate cause is the fluid from the exhalations:
like the blood and the semen in the generation
of animals. But these exhalations and the
fluids produced from them enter bodies often
and change them into marchasites1 and they
pass into veins (we find many instances of tim-
ber so transformed), into appropriate matrices
within bodies, and these metals are formed;
oftenest they enter the more interior and more
homogeneous matter of the globe, and in time
there results a vein of iron, or loadstone is pro-
duced, which is nothing but a noble iron ore;
and for this reason and also on account of its
matter being quite peculiar and distinct from
that of all other metals, nature very seldom or
never mingles with iron any other metal,
though the other metals are very often com-
mingled in some small proportion and are pro-
duced together. Now, when these exhalations
or fluids happen to meet efflorescences altered
from the homogeneous matter of the globe —
sundry precipitates, and salts, in suitable mat-
rices (operant forms) — the other metals are
produced (a specificating nature operating in
that place). For within the globe are hidden
the principles of metals and stones, as at the
earth's surface are hidden the principles of
1 The crystallized form of iron pyrites.
herbs and plants. And earth dug from the bot-
tom of a deep pit, where there appears to be
no chance of any seed being formed, produces,
if strewn on the top of a very high tower, green
herbage and unbidden grasses, the sun and the
sky brooding over earth; the earth regions pro-
duce those things which in each are spontane-
ous; each region produces its own peculiar
herbs and plants, its own metals.
Do you not see how Tmolus sends fragrant
saffron, India its ivory, the Sabaens their frankin-
cense, the naked Chalybes iron, Pontus the malo-
dorous castor, Epirus the mares that have won at
Olympia? (Virgil, Georgics, [1.56-59]. )
What the chemists (as Geber and others)
call the fixed earthy sulphur in iron is nothing
else but the homogenic matter of the globe
held together by its own humour, hardened by
a second humour: with a minute quantity of
earth-substance not lacking humour is intro-
duced the metallic humour. Hence it is said
very incorrectly by many authors that in gold
is pure earth, in iron impure; as though nat-
ural earth and the globe itself were become in
some incomprehensible sense impure. In iron,
especially in best iron, is earth in its true and
genuine nature. In the other metals is not so
much earth as, instead of earth and precipitate,
condensed and (so to speak) fixed salts, which
are efflorescences of the earth, and which also
differ in firmness and consistence. In mines
they ascend in great volume, with double hu-
mour from the exhalations; in the subterra-
nean spaces they are consolidated into metallic
ores; so too they are produced together, and in
virtue of their place and of the surrounding
bodies, they acquire, in natural matrices, their
specific forms.
Of the various bodily constitutions of load-
stones, their different substances, colours, and
properties, we have spoken before: but now af-
ter having declared the cause and origin of
metals, the matter of iron, not in the smelted
metal but in the ore from which that is ob-
tained by smelting, has to be examined. Iron,
that from its colour appears pure, is found in
the earth; yet it is not exactly metallic iron, not
quite suitable for the different uses of iron.
Sometimes it is found covered with a white
moss-like substance, or with a coating of other
stones.
Such ore is often seen in the sands of rivers:
such is the ore from Noricum (the region south
of the Danube, watered by the Inn and the
Drave; mostly comprised in the modern Aus-
ON THE LOADSTONE
tria). Iron ore, nearly pure, is often mined in
Ireland: from this the smith, without the labor
of the furnace, forges in his shop iron imple-
ments. From an ore of liver colour is very often
obtained in France an iron with bright scales
(bracteci)\ such iron is made in England
without the scales; carpenters use it instead of
chalk. In Sussex, in England, is a rich ore of
dark, and one of pale ashy colour; both of these
ores when made red hot for some time, or when
kept in a moderate fire, take the colour of liver:
in Sussex also is a dark-coloured ore in square
masses, with a black rind of harder material.
The liver-like ore is often mixed with other
stones in various ways, as also with perfect
loadstone, which yields the best iron. There is
likewise rust-coloured ore, ore of a lead colour
mixed with black, simply black, or black mixed
with cobalt; there is also an ore with admixture
of pyrites or sterile plumbago. One kind of ore
resembles jet, another the precious stone hcema-
tites. The stone smiris (emery; corundum)
used by workers in glass for glass-cutting and
called by the English emerdstone and by the
Germans smeargel, is of iron, albeit iron is
smelted from it with difficulty; it attracts an
unmagnetized needle. It is often found in deep
silver and iron mines. Thomas Erastus tells of
having been informed by a certain learned
man, of iron ores, in colour resembling metallic
iron, but quite soft and greasy, capable of being
moulded with the fingers like butter; we have
seen ores of about the same kind that were
found in England: they resemble Spanish soap.
Besides the numberless forms of stony ores,
there is a substance like iron rust deposited
from ferriferous water: it is got from mud,
loam, and from ochre. In England, a good deal
of iron is obtained in the furnace from sand
stones and clayey stones that appear to con-
tain not so much iron as sand, marl, or other
mud. In Aristotle's book De admirandis narra-
tionibus, we read:
'Tis said the iron of the Chalybes and the
Myseni has quite a peculiar origin, being car-
ried in the gravel of the streams. Some say that,
after being merely washed, it is smelted in the
furnace; others that it is washed repeatedly, and
as often the residue treated with fire in the fur-
nace, together with the stone pyrimachus (a
stone refractory to the action of fire), which
occurs there in great abundance. Thus do
many sorts of substances contain in themselves
strikingly and most plentifully this ferric and
telluric element. Many, too, and most plentiful
in every soil are the stones and earths and the
various bodies and compounds, which contain
iron (though not in such abundance) and yield
it in the furnace fire, but which are reject-
ed by the metallurgist as not workable with
profit; and there are other earths that give
evidence of the presence of iron in them;
these, being very poor in the metal, are not
smelted at all, and not being esteemed they
are not known.
The kinds of manufactured iron differ very
much from one another. For one kind has
great tenacity; and that is the best. There is a
medium kind. Another kind is brittle; that is
the worst. Sometimes the iron, on account of
the excellence of the ore, is made into steel; as
in Noricum at present. From the best iron also,
worked over and over again, and purged of
all impurities, or plunged red-hot into water,
is produced what the Greeks call <rrojua>/ja
and the Latins acies and aciarium [steel], and
which is variously called Syrian, Parthian,
Norican, Comese and Spanish; in other places
it takes its name from the water in which it is
repeatedly immersed, as at Como in Italy, and
Bilbao and Tariassone in Spain. Steel sells at a
far higher price than iron. And, on account of
its superiority, it is in better accord with the
magnet. It is often made from powerful load-
stone, and it acquires the magnetic virtue
readily, retains it a long time unimpaired and
fit for all magnetic experiments.
The iron, after it has been smelted in the
first furnace, is then treated with various
processes in great forges or mills, the metal
under mighty blows acquiring toughness, and
dropping its impurities. When first smelted it
is brittle and by no means perfect. Therefore,
here in England, when great cannons are cast,
in order that they may be able to withstand
the explosive force of the ignited gunpowder,
the metal is specially purged of impurities:
while fluid it is made to pass a second time
through a narrow opening, and thus is freed of
recremental substances. Smiths, with the use of
certain liquids and hammer-strokes, toughen
the iron laminae from which are made shields
and coats of mail not penetrable by any
musket-ball. Iron is made harder by skill and
tempering; but skill also makes it softer and as
pliant as lead. It is made hard by certain
waters into which it is plunged at white heat,
as in Spain. It is made soft again either by fire
alone when, without hammering and without
the use of water, it is allowed to grow cool;
or by being dipped in grease; or it is variously
tempered, to serve the purposes of the different
i6
WILLIAM GILBERT
arts, by being smeared with special prepara-
tions. This art is described by Baptista Porta
in Book XIII of the Magia naturalis.
Thus is this ferric and telluric substance con-
tained in and extracted from various kinds of
stones, ores, and earths; thus too does it differ
in appearance, form, and efficiency; and by
various processes of art it is smelted and puri-
fied and made to serve man's uses in all sorts of
trades and in all sorts of tools, as no other body
can serve. One kind of iron is suitable for
breastplates, another withstands cannon balls,
another protects against swords or the curved
blades called scimitars; one kind is used in
making swords, another in forging horseshoes.
Of iron are made nails, hinges, bolts, saws,
keys, bars, doors, folding-doors, spades, rods,
pitchforks, heckles, hooks, fish-spears, pots,
tripods, anvils, hammers, wedges, chains, man-
acles, fetters, hoes, mattocks, sickles, hooks for
pruning vines, and for cutting rushes, shovels,
weeding-hooks, ploughshares, forks, pans,
ladles, spoons, roasting-spits, knives, dag-
gers, swords, axes, Celtic and Gallic darts,
Macedonian pikes, lances, spears, anchors and
many nautical implements; furthermore, bul-
lets, javelins, pikes, corselets, helmets, breast-
plates, horseshoes, greaves, wire, strings of
musical instruments, armchairs, portcullises,
bows, catapults, and those pests of humanity,
bombs, muskets, cannon-balls, and no end of
implements unknown to the Latins.
I have recounted so ma'ny uses in order that
the reader may know in how many ways this
metal is employed. Its use exceeds that of all
other metals a hundredfold ; it is smelted daily ;
and there are in every village iron forges. For
iron is foremost among metals and supplies
many human needs, and they the most press-
ing: it is also far more abundant in the earth
than the other metals, and it is predominant.
Therefore it is a vain imagination of chemists
to deem that nature's purpose is to change all
metals to gold, that being brightest, heaviest,
strongest, as though she were invulnerable,
would change all stones into diamonds because
the diamond surpasses them all in brilliancy
and in hardness. Iron ore, therefore, as also
manufactured iron, is a metal slightly different
from the primordial homogenic telluric body
because of the metallic humour it has imbibed;
yet not so different but that in proportion as
it is purified it takes in more and more of
the magnetic virtues, and associates itself
with that prepotent form and duly obeys the
same.
CHAPTER 8. In what countries and regions
iron is produced
IRON mines are very numerous everywhere —
both the ancient mines mentioned by the earli-
est writers and the new and modern ones. The
first and greatest were, I think, in Asia, for in
the countries of Asia, which naturally abound
in iron, government and the arts did most
flourish; and there were the things needful for
man's use first discovered and sought for. It is
related that iron existed in the neighbourhood
of Andria; in the land of the Chalybes, on the
banks of the river Thermodon in Pontus; in
the mountains of Palestine on the side toward
Arabia; in Carmania. In Africa, there was an
iron mine in the island of Meroe. In Europe,
iron was found in the hills of Britain, as Strabo
writes; in hither Spain, in Cantabria; among
the Petrocorii and the Cabi Bituriges in Gaul
were smithies in which iron was made. In
Germany was a mine near Luna, mentioned by
Ptolemy; the Gothinian iron is spoken of by
Cornelius Tacitus; and the iron of Noricum is
famed in poesy; there was also iron in Crete
and in Eubcea. Many other mines, neither
meagre nor scant, but of vast extent, were over-
looked by writers or were unknown to them.
Pliny calls hither Spain and the whole region
of the Pyrenees an iron country; and he says
that, in the part of Cantabria washed by the
ocean, there is a mountain steep and high
which (wonderful to tell) is all iron. The earli-
est mines were iron mines, not mines of gold,
silver, copper or lead: for iron is more sought
after for the needs of man; besides, iron mines
are plainly visible in every country, in every
soil, and they are less deep and less encom-
passed with difficulties than other mines.
But were I simply to enumerate modern iron
mines and those worked in our own time, a
very large book would have to be written, and
paper would fail me before iron: yet each one
of these mines could supply a thousand forges.
For among minerals there is no other substance
so plentiful: all metals and all stones distinct
from iron ore are surpassed by ferric and fer-
ruginous substances. For you cannot easily find
a district, hardly a township, throughout all
Europe, if you search thoroughly, that has not
a rich and plentiful vein of iron, or that does
not yield an earth either saturated with iron-
rust or at least slightly tinctured with it. That
this is so, is easily shown by any one versed in
metallurgy and chemistry.
Besides iron and its ore, there is another fer-
ric substance, which, however, does not yield
ON THE LOADSTONE
the metal, because the thin humour is burnt up
by the fierce fires and is converted into dross
like that separated from the metal when first
smelted. Such is the white clay and argillaceous
earth which is seen to make up a great part of
our British island; this, if treated with strong
heat, either exhibits a ferric and metallic body,
or is transformed into a ferric vitrification: this
fact can be verified in houses built of brick, for
the bricks that in the kiln are laid nearest to the
fires, and are there burnt, show ferric vitrifica-
tion at their other end, which grows black.
Furthermore, all those earths when prepared
are attracted by the magnet like iron. Lasting
and plentiful is the earth's product of iron.
Georgius Agricola says that nearly all moun-
tainous regions are full of its ores; and we our-
selves know that a rich iron ore is often dug in
the lowlands and plains throughout England
and Ireland, as Agricola tells of iron being dug
in the meadows near the town of Saga out of
ditches not more than two feet deep. Nor is
iron lacking, as some say, in the West Indies;
but, there, the Spaniards, intent on gold, avoid
the toilsome manufacture of iron and do not
search for rich iron ores and mines. It is prob-
able that nature and the terrestrial globe can-
not repress, but is ever sending forth into the
light a great quantity of its own native sub-
stance, and that this action is not entirely im-
peded by the pressure of the mingled sub-
stances and efflorescences at the circumference.
But iron is produced not only in the common
mother (the globe of earth), but sometimes is
also in the air, in the uppermost clouds from
the earth's vapours. It rained iron in Lucania
the year that Marcus Crassus met his death.
They tell, too, of a mass of iron, resembling
slag, having fallen out of the air in the Neth-
orian forest near Grina, which is said to have
weighed several pounds; and that it could not
be carried to that village it was so heavy, and
could not be taken on a wagon because there
were no roads. This happened before the civil
war of the Saxons, waged by the dukes. A sim-
ilar occurrence is mentioned by Avicenna. In
the Torinese, it once rained iron at several
points, some three years before that province
was conquered by the king. In the year 1510,
as Cardan relates in his book De rerum varie-
tatc, there fell from the sky, upon a field near
the river Abdua, 1200 stones, one of which
weighed 120, another 30 or 40 pounds, all of
them the colour of iron and exceedingly hard.'
These occurrences, because they happen sel-
dom, seem to be portents, like the earth-rains
and stone-showers mentioned in the annals of
the Romans. But that it ever rained other met-
als is not mentioned; for it does not appear
that gold, silver, lead, tin, or zinc ever fell from
heaven. But copper has sometimes been ob-
served to fall from the clouds — a metal differ-
ing not much from iron: and this cloud-
gendered iron and copper are seen to be imper-
fect metals, absolutely infusible and unforge-
able. For the earth, in its eminences, abounds
in store of iron, and the globe contains great
plenty of ferric and magnetic matter. Exhala-
tions of such matter sent forth with some vio-
lence may, with the concurrence of powerful
agencies, become condensed in the upper re-
gions, and so may be evolved a certain mon-
strous progeny of iron.
CHAPTER 9. Iron ore attracts iron ore
LIKE the other metals, iron is obtained from
various substances — stones, earths, and such-
like concretions, called by miners ores, or veins,
because they are produced in fissures of the
earth. Of the diversity of ores we have already
spoken. A piece of crude iron ore of the colour
of iron and rich as miners say, when floated in
a bowl or other vessel in water (as in the case
of the loadstone supra) is usually attracted by
a like piece of ore held in the hand and
brought near to it, but it is not attracted strong-
ly and with rapidity as a loadstone is drawn
by a loadstone, but slowly and weakly. Stony
ores, and those of an ashy, brown, ruddy, etc.,
colour, neither attract one another nor are at-
tracted even by a powerful loadstone, any more
than so much wood or lead or silver or gold
would be. Take some pieces of such ores and
roast or rather heat them in a moderate fire so
that they may not suddenly split or fly to pieces,
and retain them ten or twelve hours in the fire,
which is to be kept up and moderately in-
creased; then suffer them to cool, according to
the method given in Book III, Of Direction:
these stones so manipulated, the loadstone now
attracts; they show mutual sympathy, and,
when arranged according to artificial condi-
tions, they come together through the action of
their own forces.
CHAPTER 10. Iron ore has and acquires poles,
and arranges itself with reference to the earth's
poles
MEN are deplorably ignorant with respect to
natural things, and modern philosophers, as
though dreaming in the darkness, must be
aroused and taught the uses of things, the deal-
i8
WILLIAM GILBERT
ing with things; they must be made to quit
the sort of learning that comes only from
books, and that rests only on vain arguments
from probability and upon conjectures. For
the science of iron (than which nought is more
in use among us), as of many other bodies, re-
mains unknown — iron, I say, whose rich ore,
by an inborn force, when floated in a vessel on
water, assumes, like the loadstone, a north and
south direction, coming to a standstill at those
points, whence if it be turned away, it goes
back to them again in virtue of its inborn ac-
tivity. But of less perfect ores which, however,
under the guise of stone or earth contain a good
deal of iron, few possess the power of move-
ment; yet when treated artificially with fire,
as told in the foregoing chapter, these acquire
polar activity, strength ( verticity, as we call it) ;
and not only such ores as miners seek, but even
earths simply impregnated with ferruginous
matter, and many kinds of rock, do in like
manner (provided they be skilfully placed),
tend and glide toward those positions of the
heavens, or rather of the earth, until they reach
the point they are seeking: there they eagerly
rest.
CHAPTER 11. Wrought-iron, not magnetized by
the loadstone, attracts iron
IRON is extracted in the first furnace from the
ore, which is converted or separated partly into
metal, partly into dross, by the action of very
great heat continued for eight, ten, or twelve
hours. The metal flows out, leaving behind the
dross and useless substances, and forms a great
long mass, which under the blows of a large
hammer is cut into pieces: from these, after
being reduced in another furnace and again
put on the anvil, the workmen form cubical
masses, or more usually bars, which are sold to
merchants and blacksmiths: from these blocks
or bars are everywhere made in smiths' shops
various implements. This we call wrought-
iron, and, as every one knows, it is attracted by
the loadstone. But we, steadily trying all sorts
of experiments, have discovered that mere iron
itself, magnetized by no loadstone, nor impreg-
nated with any extraneous force, attracts other
iron, though it does not seize the other iron as
eagerly nor as suddenly pulls it to itself as
would a strong loadstone.
That this is so you may learn from the fol-
lowing experiment: a small piece of cork,
round, and the size of a filbert, has an iron
wire passed through it to the middle of the
wire: float this in still water and approach
(without contact) to one end of that wire, the
end of another wire: wire attracts wire, and
when the one is withdrawn slowly the other
follows, yet this action takes place only within
fit limits. In the figure, A is the cork holding
the wire, B one end of the wire rising a little
out of the water, C the end of the second wire,
which pulls B. You may demonstrate the same
thing with a larger mass of iron. Suspend in
equilibrium with a slender silken cord a long
rod of polished iron, such as are used to sup-
port hangings and curtains; bring within the
distance of half a finger's length of one end of
this as it rests still in the air, some oblong mass
of polished iron with suitable end: the balanced
rod returns to the mass; then quickly with-
draw your hand with the mass in a circular
track around the point of equilibrium of the
suspended rod, and the cord holding the rod
will travel in a circle.
CHAPTER 12. A long piece of iron, even not
magnetized, assumes a north and south direc-
tion
ALL good and perfect iron, if it be drawn out
long, acts like a loadstone or like iron rubbed
with loadstone: it takes the direction north
and south — a thing not at all understood by
our great philosophers who have laboured in
vain to demonstrate the properties of the load-
stone and the causes of the friendship of iron
for the loadstone. Experiment can be made
either with large or small objects of iron, either
in air or in water. A straight rod of iron six
feet in length and as thick as one's finger is (as
described in the foregoing chapter) suspended
in exact equilibrium with a fine but strong silk
thread. The thread, however, should be com-
posed of several silk filaments, twisted differ-
ently and not all in one direction. Let the ex-
periment be made in a small room with doors
and windows all closed, to prevent currents of
air in the room: hence it is not well to experi-
ment on windy days or when a storm is brew-
ing. The rod of iron freely acts according to its
property and moves slowly until at last coming
to a stop at its goals it points north and south,
like magnetized iron in a sun-dial, a common
magnetic compass, and the mariner's com-
ON THE LOADSTONE
pass. You may, if you arc curious of such
experiments, suspend at once from slender
threads, iron rods, or wires, or knitting-nee-
dles: you shall find them all in accord unless
there is some flaw in the conduct of this inter-
esting experiment; for unless you make all the
preparations precisely and exactly, your labour
will be vain. Test the thing in water also: here
the result is more sure and more easily ob-
tained. Pass through a round cork an iron wire
two or three fingers long, more or less, so that
it may just float in water: the moment you put
it in the water it turns round on its centre, and
one end of the wire travels to the north, the
other to the south: the cause of this, you will
find later, when we treat of the reasons of the
loadstone's directions. And it is well to know
and to hold fast in memory, that as a strong
loadstone and iron magnetized by the same,
point not always toward the true pole, but ex-
actly to the point of variation; likewise will a
weaker loadstone and iron that directs itself by
its own force, and not by force derived from
the impress of any magnet; so, too, all iron
ores, and all substances imbued with any ferric
matter and duly prepared, turn to the same
point in the horizon — to the place of varia-
tion of the locality concerned (if variation
exist there), and there they remain and rest.
CHAPTER 13. Smelted iron has in if self fixed
north and south parts, magnetic activity, ver~
ticity, and fixed vertices or poles
IRON takes a direction toward north and south,
but not with the same point directed toward
either pole; for one end of a piece of iron ore
or of an iron wire steadily and constantly points
to the north and the other to the south, whether
it be suspended in air, or floating in water,
and whether the specimens be iron bars or thin
wires. Even an iron rod or wire ten, twenty,
or more ells in length will point with one ex-
tremity to the north, with the other to the
south. And if you cut off a part, if the farther
end of that piece is boreal (northern), the
farther end of the other piece, with which it
was before joined, will be austral (southern).
And so, if you divide the rod or wire into sev-
eral pieces, you shall know the poles even be-
fore you make an experiment by floating the
pieces in water. In all these fragments a boreal
end attracts an austral, and repels a boreal, and
vice versa, according to magnetic law. But,
herein, manufactured iron so differs from load-
stone and iron ore, that in a ball of iron of
whatever size — e.g., bombs, cannon-balls, cul-
verin balls, falcon balls — polarity (verticity) is
less easily acquired and less readily manifested
than in the loadstone itself, in ore, and in a
round loadstone; but in iron instruments of
any length the force is at once seen: the cause
of which, as also the modes of acquiring polar-
ity and poles without a loadstone, together
with the account of all other recondite facts
touching verticity, we will set forth when we
come to treat of the movement of direction.
CHAPTER 14. Of other properties of the
loadstone and of its medicinal virtue
DIOSCORIDES tells that loadstone blended in
water is administered in a dose of three oboli
to expel gross humours. Galen writes that it
has virtues like those of bloodstone. Others say
that loadstone causes mental disturbance and
makes people melancholic, and often is fatal.
Gartias ab Horto does not think it injurious or
unwholesome. The people of East India, he
says, declare that loadstone taken in small
quantity preserves youthfulness: for this rea-
son the elder King Zeilam (Zeilan) is said to
have ordered made of loadstone some pans for
cooking his food (victus). "The man who was
ordered to do this thing told me," says Gartias.
Many are the varieties of loadstone, produced
by different mixtures of earths, metals, and
humours; therefore are they totally different in
their virtues and effects, according to the
neighbourhoods of places and the nearness of
adhering bodies, and the pits themselves — un-
clean matrices, as it were. Hence one load-
stone is able to purge the bowels, and another
loadstone to stay the purging; with a sort of
fumes, it can gravely affect the mind; it may
corrode the stomach and produce in it serious
disease: for such disorders, quacks prescribe
gold and emerald, practising the vilest impos-
ture for lucre's sake. Pure loadstone also may
be harmless; and not only that, but many cor-
rect excessive humours of the bowels and
putrescence of the same, and may bring about
a better temperature: such loadstones are the
Oriental ones from China, the more compact
loadstones of Bengal: these kinds of loadstone
are not distasteful nor ungrateful to the senses.
Plutarch and Caius Ptolemy, and all the copy-
ists that came after them, believe that loadstone
rubbed with garlic does not attract iron. Hence
some writers conjecture that garlic is of service
against the harmful action of loadstone: in this
way does many an untrue and vain opinion in
philosophy take its rise in fables and false-
hoods. Not a few physicians have thought that
20
loadstone has power to extract an iron arrow-
head from a human body: but a loadstone at-
tracts when it is whole, not when reduced to
powder, deformed, buried in a plaster; for it
does not with its matter attract in such case,
but serves rather to heal the ruptured tissues by
exsiccation, so causing the wound to close and
dry up, whereby the arrow-head becomes fixed
in the wound. Thus do pretenders to science
vainly and preposterously seek for remedies,
ignorant of the true causes of things.
Headaches, despite the opinion of many, are
no more cured by application of a loadstone,
than by putting on the head an iron helmet or
a steel hat. Administration of loadstone to
dropsical persons is either an error of the an-
cients or a blundering quotation of their tran-
scribers, albeit a loadstone may be found cap-
able of purging the bowels, after the manner of
sundry metallic substances: but the effect
would be due to some vice of the stone, not to
its magnetic force. Nicolaus puts into his "di-
vine plaster" a good deal of loadstone, as do
the Augsburg doctors in their "black plaster"
for fresh wounds and stabs; because of the ex-
siccating effect of the loadstone without cor-
rosion, it becomes an efficacious and useful
remedy. Paracelsus, in like manner and for the
same end, makes loadstone an ingredient of
his plaster for stab-wounds.
CHAPTER 15. The medicinal power of the iron
IT will not be alien to our purpose to treat
briefly of the medicinal power of iron; for it is
beneficial in many diseases of the human sys-
tem, and by its virtues, both natural and ac-
quired through fit and skilful preparation, it
brings about wonderful changes in the human
body; so that we may more clearly describe its
nature through its medicinal power and by
means of a few well-known experiments; to
the end that even those prentices of medicine
who abuse this most excellent medicinal agent
may learn to prescribe it more judiciously, for
the curing of patients, not as is too often the
case, to their destruction. The best iron, *>.,
stomoma, chalybs, acies, or aciarium [steel], is
reduced by filing to a fine powder; this pow-
der has strongest vinegar poured on it, is dried
in the sun, again treated with vinegar, and
once more dried. Then it is washed in spring
water or other water at hand, and dried. It is
again pulverized and pounded fine on por-
phyry, sifted through a fine sieve, and kept for
use. It is given chiefly in cases of lax and over-
humid liver, and in cases of tumid spleen after
WILLIAM GILBERT
suitable evacuations; hence young women of
pale, muddy, blotchy complexion are by it re-
stored to soundness and comeliness, for it is
highly exsiccative and harmlessly astringent.
But some, who in every internal disorder
always recognize obstructions of liver and
spleen, think it beneficial in such cases, as re-
moving obstructions; and herein they accept
the opinions chiefly of certain Arabic writers.
Hence in cases of dropsy, schirrus of the liver,
of chronic jaundice, and hypochondriac melan-
cholia, or complaints of the oesophagus, they
prescribe it, or add it to electuaries, often to the
sure destruction of many a patient. Fallopius
recommends a preparation of iron of his own
for schirrus of the spleen; but he is much mis-
taken, for though loadstone is exceedingly
beneficial where the spleen is lax and tumid on
account of humours, so far is it from curing a
spleen thickened to a schirrhus, that it makes the
mischief far worse; for agents that are greatly
siccative and that absorb humours, transform
viscera that have been thickened by schirrhus,
into the hardness almost of a stone. Some there
are who dry it at a high temperature in an
oven, burning it till its colour is changed to
red: it is then called "saffron of Mars,"1 and is
a very powerful exsiccant and quickly pene-
trates the intestines. Further, they prescribe vio-
lent exercise so that the remedy may enter the
heated intestines and reach the part affected.
Hence it is reduced to a very fine powder; else
it would remain in the oesophagus and in the
chyle and would not penetrate to the intestines.
Therefore this dry, earthly medicament is
proved by the most conclusive tests to be, after
due evacuations, a remedy in diseases arising
from humour (when the intestines are running
and overflowing with morbid fluids). A prep-
aration of steel is indicated for tumid spleen;
chalybeate waters also reduce the spleen, al-
beit, as a rule, iron is of frigid efficiency and a
constringent rather than a resolvent; but it does
this neither by heat nor by cold, but by its own
dryness when mixed with a penetrant fluid; in
this way it dissipates humours, thickens the
villi; strengthens the fibres and when they are
lax makes them contract; then the natural
warmth in the organs thus strengthened be-
coming stronger does the rest; but should the
liver be indurated and impaired through age
or chronic obstruction, or should the spleen be
dried up and thickened into a schirrhus, under
which complaints the flesh parts of the mem-
bers become atrophied, and water collects all
1Sec Book n, Chap. xxm.
ON THE LOADSTONE
over the body under the skin — in such cases the
preparation of steel does but hasten a fatal re-
sult and makes the mischief worse. Some re-
cent authorities prescribe, as a highly com-
mended and celebrated remedy for dried-up
liver, an electuary of iron slag described by
Razes (Rhazes — Abu Bekr Arrasi) in book
ninth Ad Almansorem , or of prepared steel fil-
ings: bad and pernicious counsel. But now if
they never will learn from our philosophy, at
least daily experience and the decline and death
of their patients will convince them, slow and
sluggish as they are.
Whether iron be warm or cold is a question
over which many contend. Manardus, Curtius,
Fallopius, and others bring many arguments
for both sides: every one judges according to
his own way of looking at it. Some will have it
cold, saying that iron has the power of refrig-
eration, since Aristotle in the Meteorology
declares it to belong to the class of bodies that
become concreted through cold by emission of
all their warmth. Galen, too, says that iron gets
its consistency from cold; further, that it is an
earthy body and dense. It is declared to be cold
also because it is astringent, and because chaly-
beate water stills thirst; they mention also the
sensation of coolness produced by thermic chaly-
beate waters. But others hold it to be warm,
since Hippocrates says that chalybeate waters
issuing from places where iron exists are warm.
Galen says that in all metals there is much sub-
stance or essence of fire. Razes will have it that
iron is warm and dry in the third degree. The
Arabs hold that iron opens the spleen and the
liver: hence it is warm. Montagnana recom-
mends it for frigid complaints of uterus and
oesophagus. And thus do sciolists wrangle with
one another, and confuse the minds of learners
with their questionable cogitations, and debate
over the question of goat's wool, philosophiz-
ing about properties illogically 'inferred and
accepted: but these things will appear more
plainly when we come to treat of causes, the
murky cloud being dispersed that has so long
involved all philosophy. Iron filings, iron scales,
iron dross, do not, says Avicenna, lack harmful
quality (perhaps when they are not properly
prepared, or are taken in too large doses), hence
they produce violent intestinal pains, roughness
in the mouth and on the tongue, marasmus,
and drying up of the members. But mistakenly
and old womanishly does Avicenna declare
that the true antidote of this ferric poison is a
drachm of loadstone taken in a draught of the
juice of dog's mercury or of beet-root; for load-
21
stone too is of a twofold nature, and often is in-
jurious and fatal in its effects; neither does it
withstand iron, for it attracts it; nor is it able
to attract when drunk as a powder in liquid;
rather does it cause the self -same mischiefs
CHAPTER 16. That loadstone and iron ore are
the same, and that iron is obtained jrom both,
life other metals from their ores; and that all
magnetic properties exist, though weaker, both
in smelted iron and in iron ore
So far we have been telling of the nature and
properties of loadstone, as also of the properties
and nature of iron; it now remains that we
point out their mutual affinities — their consan-
guinity, so to speak — and that we show the two
substances to be very nearly allied. In the up-
permost part of the terrestrial globe or its su"
perficies of detritus — its rind as it were — these
two bodies come into being and are generated
in the same matrix, in one bed, like twins.
Strong loadstones are mined from separate de-
posits, and weaker loadstones also have their
own beds. Both occur in iron mines. Iron ore
occurs usually by itself, unaccompanied by
strong loadstone (for the more perfect load-
stones occur more rarely). A strong loadstone
looks like iron: from it is often made the best
iron, which the Greeks call stomoma, the Lat-
ins acies, and the Barbarians, not inappropri-
ately, aciare or aciarium. This stone attracts
and repels other loadstones, and governs their
directions; points to the earth's poles, attracts
molten iron, and does many other wonderful
things, some of which we have already men-
tioned, but many more remain yet to be pointed
out. A weak loadstone will do the same, but
less forcefully: and iron ore, and also smelted
iron (if they be prepared), show their virtues
in all magnetic experiments, no less than do
weak magnets; and the inert iron ore, endowed
with no magnetic powers, that is taken out of
the mine, becomes awake when treated in the
furnace and fittingly prepared, and then is a
loadstone in power and properties. Sometimes
ironstone or iron ore exerts attractive action
the moment it comes from the mine, and with-
out being prepared in any way; native iron,
also, or ore of iron colour, attracts iron and
makes it point to the poles. Thus the form, ap-
pearance, and essence are one. For to me there
seems to be greater difference and unlikeness
between a very strong loadstone and a weak
one that is hardly able to attract a single parti-
cle of iron filings; between a hard, firm, and
metallic loadstone and one that is soft, friable,
22
clayey, with so great a difference between them
in colour, substance, qualities and weight; than
between the best ore, rich in iron, or iron that
from the first is metallic, on the one hand,
and the best loadstone on the other. Nay, the
two are usually not to be distinguished by any
signs, nor can miners tell one from the other,
for they agree in all respects.
Further, we see both the finest magnet and
iron ore visited as it were by the same ills and
diseases, aging in the same way and with the
same indications, preserved by the same reme-
dies and protective measures, and so retaining
their properties: so, too, the one adds to the
other's power and intensifies and increases it,
when the two are artificially connected. For
they are both impaired by the action of acrid
liquids as though by poisons; the aqua jortis
of the chemists does equal injury to both; ex-
posed for a long time to the action of the at-
mosphere they both, in equal degree, age as it
were and decline; each is saved from impair-
ment by being kept in the dtbris and scrapings
of the other, and a suitable piece of steel or iron
being applied to its pole, the magnetic power is
intensified by the steadfast union. A loadstone
is kept in iron filings not as though it fed on
iron, or as though it were a living thing need-
ing victual, as Cardan philosophizes; neither
because thus it is protected from the injurious
action of the atmosphere (wherefore both the
loadstone and iron are kept in bran by Scaliger ;
though Scaliger is mistaken here, for they are
not best preserved so, and loadstone and iron
in some of their forms last a long time); but
because each is kept unimpaired in filings of
the other and their extremities do not become
weak, but are cherished and preserved. For as
in their native sites and mines, similar bodies
surrounded by other bodies of the same kind,
e.g., the minor interior parts of some great
mass, endure for ages whole and undecayed;
so loadstone, and iron ore, when buried in a
like material, do not part with their native hu-
mour, and do not become weak, but retain
their original properties. A loadstone packed
in iron filings, as also iron ore in scrapings of
loadstone, and manufactured iron in the same
or in iron filings, lasts longer.
Thus these two associated bodies possess the
true, strict form of one species, though, because
of their outwardly different aspect and the in-
equality of the self-same innate potency, they
have hitherto been by all held to be different,
and by sciolists to be specifically different, for
sciolists have not understood that in both sub-
WILLIAM GILBERT
stances reside exactly the same potencies, dif-
fering however in strength. They are in fact
true parts and intimate parts of the globe, re-
taining nature's primal powers of mutual at-
traction, of mobility, and of ordering them-
selves according to the position of the globe it-
self: these powers they impart to each other,
enhancing each other's powers, confirming
them, taking them from each other, and hold-
ing them. The stronger invigorates the weaker,
not as if it imparted of its own substance or
parted with aught of its own strength, neither
by injecting into that other any physical sub-
stance; but the dormant power of one is awak-
ened by the other's without expenditure. For
if with one loadstone you magnetize one thou-
sand compass needles for mariners' use that
loadstone not less powerfully attracts iron than
it did before; with one stone weighing a pound
any one can suspend in air 1000 pounds of iron.
For if one were to drive into a wall a number
of iron nails weighing all together 1000 pounds,
and were to apply to them an equal number of
other nails properly magnetized by contact
with a loadstone, the nails would plainly hang
suspended in air through the power of one sin-
gle stone. Hence this is not the action, work,
or outlay of the loadstone solely, for the iron,
which is something extracted from loadstone,
a transformation of loadstone into metal, and
which gains force from the loadstone and
(whatever ore it may have been derived from)
by its proximity strengthens the loadstone's
magnetic power, at the same time enhances its
own native force by the proximity of the load-
stone and by contact therewith, even though
solid bodies intervene between them. Iron
touched by loadstone renovates other iron by
contact and gives it magnetic direction; and
that does the same for a third piece of iron. But
if you rub with loadstone any other metal, or
wood, or bone, or glass, as they will not move
toward a fixed and determinate quarter of the
heavens, nor will be attracted by a magnetized
body; so they cannot impart by attrition or by
infection any magnetic property either to other
bodies or to iron itself.
Loadstone differs from iron ore, as also from
some weak loadstones, in that when reduced in
the furnace to a ferric and metallic molten
mass, it does not always assume readily the
fluid condition and become changed to metal,
but sometimes is burnt into ash in the large
furnaces: this, either because of a certain ad-
mixture of sulphurous matter, or because of its
own excellence and more simple nature; or be-
ON THE LOADSTONE
cause of the resemblance it bears to nature, and
the form it has in common with that mother
of all; for earths, ferruginous stones, and load-
stones rich in metal, are much loaded and dis-
figured with drossy metallic humours and with
foreign earthy admixtures in their substance,
like most weak magnets from the mines; hence
they are farther removed from the common
mother and are degenerate, and in the furnace
they are more easily melted and give a softer
sort of iron and no good steel. Most loadstones,
if they be not unduly burnt, yield in the furnace
the best of iron. But in all these prime qualities
iron ore agrees with loadstone, for both, being
more akin to the earth and more nearly associ-
ated to it than any other bodies around us, pos-
sess within themselves the magnetic, genuine,
homogenic, and true substance of the terres-
trial globe, less tainted and impaired by for-
eign impurities, and less mixed with the efflo-
rescences on the earth's surface and the debris
of generations of organisms. And on this
ground does Aristotle seem, in the fourth book
of his Meteorology, to distinguish iron from
all other metals. Gold, says he, silver, copper,
tin, lead, pertain to water; but iron is earthy.
Galen, in the fourth book De jacultatibus sim-
plicium medicamentorum, says that iron is an
earthy and dense body.
So, according to our reasoning, loadstone is
chiefly earthy; next after it comes iron ore or
weak loadstone; and thus loadstone is by origin
and nature ferruginous, and iron magnetic, and
the two are one in species. Iron ore in the fur-
nace yields iron; loadstone in the furnace yields
iron also, but of far finer quality, which is
called steel; and the better sort of iron ore is
weak loadstone, just as the best loadstone is the
most excellent iron ore in which we will show
that grand and noble primary properties in-
here. It is only in weaker loadstone, or iron ore,
that these properties are obscure, or faint, or
scarcely perceptible to the senses.
CHAPTER 17. That the terrestrial globe is mag-
netic and is a loadstone; and just as in our hands
the loadstone possesses all the primary powers
(forces) of the earth, so the earth by reason of
the same potencies lies ever in the same direc-
tion in the universe
BEFORE we expound the causes of the magnetic
movements and bring forward our demonstra-
tions and experiments touching matters that
for so many ages have lain hid — the real foun-
dations of terrestrial philosophy — we must for-
mulate our new and till now unheard-of view
of the earth, and submit it to the judgment of
scholars. When it shall have been supported
with a few arguments of prima jade cogency,
and these shall have been confirmed by subse-
quent experiments and demonstrations, it will
stand as firm as aught that ever was proposed
in philosophy, backed by ingenious argumen-
tation, or buttressed by mathematical demon-
strations. The terrestrial mass which together
with the world of waters produces the spheri-
cal figure and our globe, inasmuch as it con-
sists of firm durable matter, is not easily al-
tered, does not wander nor fluctuate with inde-
terminate movements like the seas and the
flowing streams; but in certain hollows, within
certain bounds, and in many veins and arter-
ies, as it were, holds the entire volume of liquid
matter, nor suffers it to spread abroad and be
dissipated. But the solid mass of the earth has
the greater volume and holds pre-eminence in
the constitution of our globe. Yet the water is
associated with it, though only as something
supplementary and as a flux emanating from
it; and from the beginning it is intimately
mixed with the smallest particles of earth and
is innate in its substance. The earth growing
hot emits it as vapour, which is of the greatest
service to the generation of things.
But the strong foundation of the globe, its
great mass, is that terrene body, far surpassing
in quantity the whole aggregate of fluids and
waters whether in combination with earth or
free (whatever vulgar philosophers may dream
about the magnitudes and proportions of their
elements); and this mass makes up most of
the globe, constituting nearly its whole inte-
rior framework, and of itself taking on the
spherical form. For the seas do but fill certain
not very deep hollows, having very rarely a
depth of a mile, and often not exceeding 100
or 50 fathoms. This appears from the observa-
tions of navigators who have with line and
sinker explored their bottoms. In view of the
earth's dimension, such depressions cannot
much impair the spheroidal shape of the globe.
Still the portion of the earth that ever comes
into view for man or that is brought to the sur-
face seems small indeed, for we cannot pene-
trate deep into its bowels, beyond the debris of
its outermost efflorescence, hindered either by
the waters that flow as through veins into great
mines; or by the lack of wholesome air neces-
sary to support the life of the miners; or by the
enormous cost of executing such vast undertak-
ings, and the many difficulties attending the
work. Thus we cannot reach the inner parts of
WILLIAM GILBERT
the globe, and if one goes down, as in a few
mines, 400 fathoms, or (a very rare thing) 500
fathoms, it is something to make every one
wonder. But how small, how almost null, is
the proportion of 500 fathoms to the earth's di-
ameter— 6872 miles — can be easily understood.
So we do only see portions of the earth's cir-
cumference, of its prominences; and every-
where these arc either loamy, or argillaceous,
or sandy; or consist of organic soils or marls;
or it is all stones and gravel; or we find rock-
salt, or ores, or sundry other metallic sub-
stances. In the depths of the ocean and other
waters are found by mariners, when they take
soundings, ledges and great reefs, or bowlders,
or sands, or ooze. The Aristotelian element,
earth, nowhere is seen, and the Peripatetics are
misled by their vain dreams about elements.
But the great bulk of the globe beneath the sur-
face and its inmost parts do not consist of such
matters; for these things had not been were it
not that the surface was in contact with and ex-
posed to the atmosphere, the waters, and the
radiations and influences of the heavenly bod-
ies; for by the action of these are they generated
and made to assume many different forms of
things, and to change perpetually. Still do
they imitate the inner parts and resemble their
source, because their matter is of the earth, al-
beit they have lost the prime qualities and the
true nature of terrene matter; and they bear
toward the earth's centre and cohere to the
globe and cannot be parted from it save by
force.
Yet the loadstone and all magnetic bodies —
not only the stone but all magnetic, homogenic
matter — seem to contain within themselves the
potency of the earth's core and of its inmost
viscera, and to have and comprise whatever in
the earth's substance is privy and inward: the
loadstone possesses the actions peculiar to the
globe, of attraction, polarity, revolution, of
taking position in the universe according to the
law of the whole; it contains the supreme ex-
cellencies of the globe and orders them: all this
is token and proof of a certain eminent com-
bination and of a most accordant nature. For, if
among bodies one sees aught that moves and
breathes and has senses and is governed and
impelled by reason, will he not, knowing and
seeing this, say that here is a man or something
more like man than a stone or a stalk? The
loadstone far surpasses all other bodies around
us in the virtues and properties that pertain to
the common mother of all; but those proper-
ties have been very little understood and noted
by philosophers. Toward it, as we see in the
case of the earth, magnetic bodies tend from all
sides, and adhere to it; it has poles — not mathe-
matical points, but natural points of force that
through the co-operation of all its parts excel in
prime efficiency; such poles exist also in the
same way in the globe, and our forefathers al-
ways sought them in the heavens. Like the
earth, it has an equator, a natural line of de-
markation between the two poles; for of all the
lines drawn by mathematicians on the terres-
trial globe, the equator (as later will appear) is
a natural boundary, and not merely a mathe-
matical circle.
Like the earth, the loadstone has the power
of direction and of standing still at north and
south; it has also a circular motion to the earth's
position, whereby it adjusts itself to the earth's
law. It follows the elevations and depressions of
the earth's poles, and conforms precisely to
them: according to the position of the earth and
of the locality, it naturally and of itself elevates
its poles above the horizon, or depresses them.
The loadstone derives properties from the earth
ex tern pore, and acquires verticity; and iron is
affected by the verticity of the globe as it is af-
fected by a loadstone. Magnetic bodies are gov-
erned and regulated by the earth, and they are
subject to the earth in all their movements. All
the movements of the loadstone are in accord
with the geometry and form of the earth and
are strictly controlled thereby, as will later be
proved by conclusive experiments and dia-
grams; and the greater part of the visible earth
is also magnetic, and has magnetic movements,
though it is defaced by all sorts of waste matter
and by no end of transformations.
Why, then, do we not recognize this primary
and homogeneous earth-substance, likest of all
substances to the inmost nature, to the very
marrow, of the earth itself, and nearest to it?
For not any of the other mixed earths — those
suitable for agriculture, — not any of the metal-
liferous veins, no stones, no sands, no other
fragments of the globe that come under our
notice, possess such stable, such distinctive vir-
tues. Yet we do not hold the whole interior of
this our globe to be of rock or of iron, albeit the
learned Franciscus Maurolycus deems the earth
in its interior to consist throughout of rigid
rock. For not every loadstone that we find is a
stone, being sometimes like a clod of earth, or
like clay, or like iron; consisting of various ma-
terials compacted into hardness, or soft, or by
heat reduced to the metallic state; and in the
earth's surface formations, according to cir-
ON THE LOADSTONE
cumstances of place, of the bodies around it,
and of its matrix in the mine, a magnetic sub-
stance is distinguished by divers qualities and
by adventitious accretions, as we see in marl, in
some stones, and in iron ores. But the true
earth-matter we hold to be a solid body homo-
geneous with the globe, firmly coherent, en-
dowed with a primordial and (as in the other
globes of the universe) an energic form. By be-
ing so fashioned, the earth has a fixed verticity,
and necessarily revolves with an innate whirl-
ing motion: this motion the loadstone alone of
all the bodies around us possesses genuine and
true, less spoilt by outside interferences, less
marred than in other bodies, — as though the
motion were an homogeneous part taken from
the very essence of our globe. This pure native
iron is produced when homogenic portions of
the earth's substance coalesce to form a metal-
lic vein; loadstone is produced when they are
transformed into metallic stone or a vein of the
finest iron or steel; so, too, rather imperfect
homogenic material collects to form other iron
ores — just as many parts of the earth, even parts
that rise above the general circumference, are
of homogenic matter, only still more debased.
Native iron is iron fused and reduced from
homogenic matters, and coheres to earth more
tenaciously than the ores themselves.
Such, then, we consider the earth to be in its
interior parts; it possesses a magnetic homo-
genic nature. On this more perfect material
(foundation) the whole world of things terres-
trial, which, when we search diligently, mani-
fests itself to us everywhere, in all the magnetic
metals and iron ores and marls, and multi-
tudinous earths and stones; but Aristotle's
"simple element," and that most vain terrestrial
phantasm of the Peripatetics, — formless, inert,
cold, dry, simple matter, the substratum of all
things, having no activity, — never appeared to
any one even in dreams, and if it did appear
would be of no effect in nature. Our philoso-
phers dreamt only of an inert and simple mat-
ter. Cardan thinks the loadstone is not a stone
of any species, but that it is, as it were, a per-
fect portion of a certain kind of earth that is
absolute, whereof a proof is its abundance, for
there is no place where it is not found. He says
that this kind of conceptive, generative earth,
possessed of an affinity like that of the marriage
tie, is perfected when it has been placed in con-
tact with, or received the fecundating influ-
ence of, the masculine or Herculean stone, it
having been, moreover, shown in a previous
proposition (Libra de proportionibus) that the
loadstone is true earth.
A strong loadstone shows itself to be of the
inmost earth, and in innumerable experiments
proves its claim to the honour of possessing the
primal form of things terrestrial, in virtue of
which the earth itself remains in its position
and is directed in its movements. So a weak
loadstone, and all iron ore, all marls and argil-
laceous and other earths (some more, some
less, according to the difference of their hu-
mours and the varying degrees in which they
have been spoilt by decay), retain, deformed,
in a state of degeneration from the primordial
form, magnetic properties, powers, that are
conspicuous and in the true sense telluric. For
not only does metallic iron turn to the poles,
not only is one loadstone attracted by another
and made to revolve magnetically, but so do (if
prepared) all iron ores and even other stones,
as slates from the Rhineland, the black slates
(ardoises, as the French call them) from An-
jou, which are used for shingles, and other sorts
of fissile stone of different colours; also clays,
gravel, and several sorts of rock; and, in short,
all of the harder earths found everywhere, pro-
vided only they be not fouled by oozy and dank
defilements like mud, mire, heaps of putrid
matter, or by the decaying remains of a mixture
of organic matters, so that a greasy slime oozes
from them, as from marl, — they are all at-
tracted by the loadstone, after being prepared
simply by the action of fire and freed from their
excrementitious humour; and as by the load-
stone, so, too, are they magnetically attracted
and made to point to the poles by the earth it-
self, therein differing from all other bodies; and
by this innate force they are made to conform
to the ordering and planning of the universe
and the earth, as later will appear. Thus every
separate fragment of the earth exhibits in in-
dubitable experiments the whole impetus of
magnetic matter; in its various movements it
follows the terrestrial globe and the common
principle of motion.
BOOK SECOND
CHAPTER 1. Of magnetic movements
OF opinions touching the loadstone and its va-
rieties; of its poles and its recognized faculties;
of iron and its properties; of the magnetic sub-
stance common to loadstone and iron and the
earth itself, we have treated briefly in the fore-
going book. Now remain the magnetic move-
ments and their broader philosophy as devel-
oped by experiments and demonstrations.
These movements are impulsions of homogene-
ous parts toward one another or toward the pri-
mary conformation of the whole earth. Aristot-
le admits only two simple movements of his ele-
ments—from the centre and toward the centre;
light objects upward, heavy objects downward:
so that in the earth there is but one motion of
all its parts toward the centre of the world,— a
wild headlong falling. We, however, will else-
where consider what this "light" may be, and
will show how erroneously it is inferred by the
Peripatetics from the simple motion of the ele-
ments; we shall also inquire what "heavy"
means.1 But now we have to inquire into the
causes of the other movements depending on its
true form: these we see clearly in all magnetic
bodies; these also we find existing in the earth
and all its homogenic parts; further, we find that
they are in accord with the earth, and are
bound up in its forces. Now five movements or
differences of movement are perceived by us:
CoinoN2 (commonly called attraction), an im-
pulsion to magnetic union; DIRECTION3 toward
the earth's poles, and verticity of the earth to-
ward determinate points in the universe, and
the standstill there; VARIATION,4 deflection
from the meridian— this we call a perverted mo-
tion; DECLINATION6 (inclination or dip), a de-
scent of the magnetic pole beneath the horizon;
and circular movement, or REVOLUTION.6 Of
each of these we .will treat separately, and will
show how they all proceed from a congregant
nature, or from verticity or from volubility.
Jofrancus Oflfusius distinguishes several magnet-
1 See Plato's Ttnueus. * See u, 2, ft seq,
1 Sec in. 4 Sec iv. * Sec v.
6 See vi, 3, ctseq.
ic movements, the first to the centre, the second
to the pole, traversing 77 degrees, the third to
iron, the fourth to a loadstone. The first is not
always to the centre, for only at the poles is it
in a right line to the centre, if the motion is
magnetic, otherwise it is only the movement of
matter toward its mass and toward the earth.
The second, of 77 degrees to the pole, is no
movement, but a direction or a variation to the
earth's pole. The third and the fourth are mag-
netic, and are but one movement. Thus this au-
thor recognizes no true magnetic movement
but coition toward iron or loadstone, commonly
known as attraction. There is another move-
ment in the earth as a whole, which does not
take place toward the terrella or the parts, i.e.,
the movement of coacervation and that move-
ment of matter called by philosophers a "right
movement": of that elsewhere.
CHAPTER 2. Of magnetic coition; and, first, of the
attraction exerted by amber ; or more properly the at-
tachment of bodies to amber
GREAT has ever been the fame of the loadstone
and of amber in the writings of the learned:
many philosophers cite the loadstone and also
amber whenever, in explaining mysteries, their
minds become obfuscated and reason can no
farther go. Over-inquisitive theologians, too,
seek to light up God's mysteries and things be-
yond man's understanding by means of the load-
stone and amber : j ust as light-headed metaphysi-
cians, when they utter and teach their vain imag-
inings, employ the loadstone as a sort of Delphic
sword and as an illustration of all sorts of things.
Medical men also (at the bidding of Galen), in
proving that purgative medicines exercise at-
traction through likeness of substance and kin-
ships of juices (a silly error and gratuitous!),
bring in as a witness the loadstone, a substance
of great authority and of noteworthy efficiency,
and a body of no common order. Thus in very
many affairs persons who plead for a cause the
merits of which they cannot set forth, bring in
as masked advocates the loadstone and amber.
But all these, besides sharing the general misap-
prehension, are ignorant that the causes of the
26
ON THE LOADSTONE
loadstone's movements are very different from
those which give to amber its properties; hence
they easily fall into errors, and by their own
imaginings are led farther and farther astray.
For in other bodies is seen a considerable power
of attraction, differing from that of the load-
stone,— in amber, for example. Of this substance
a few words must be said, to show the nature of
the attachment of bodies to it, and to point out
the vast difference between thisand the magnetic
actions; for men still continue in ignorance, and
deem that inclination of bodies toamber to bean
attraction, and comparable to the magnetic coi-
tion. The Greeks call this substance rjKtKrpov,
because, when heated by rubbing, it attracts to
itself chaff; whence it is also called &pwcx^ and
from itsgolden colour , xpwo<}>bpov. B u t the Moors
call it carabe, because they used to offer it in
sacrifices and in the worship of the gods; for in
Arabic carab means oblation, not rapiens paleas
(snatching chaff), as Scaliger would have it,
quoting from the Arabic or Persian of Abohali
(Hali Abbas). Many call this substance ambra
(amber) especially that which is brought from
India and Ethiopia. The Latin name sucdnum
appears to be formed from succus, juice. The
Sudavienses or Sudini call thesubstanceg^mter,
as though genitum terra (produced by the earth).
The erroneous opinion of the ancients as to its
nature and source being exploded, it is certain
that amber comes for the most part from the
sea: it is gathered on the coast after heavy
storms, in nets and through other means, by
peasants, as by the Sudini of Prussia ; it is also
sometimes found on the coast of our own Brit-
ain. But it seems to be produced in the earth
and at considerable depth below its surface, like
the rest of the bitumens; then to be washed out
by the sea-waves, and to gain consistency under
the action of the sea and the saltness of its wa-
ters. For at first it was a soft and viscous matter,
and hence contains, buried in its mass forever-
more (aeternis sepulchns relucentes), but still
(shining) visible, flies, grubs, midges, and ants.
The ancients as well as moderns tell (and their
report is confined by experience) that amber at-
tracts straws and chaff. The same is done by jet,
a stone taken out of the earth in Britain, Ger-
many, and many other regions: it is a hard con-
cretion of black bitumen,-— a sort of transfor-
mation of bitumen to stone. Many modern au-
thors have written about amber and jet as at-
tracting chaff and about other facts unknown to
the generality, or have copied from other writ-
ers: with the results of their labors booksellers'
shops are crammed full. Our generation has pro-
duced many volumes about recondite, abstruse,
and occult causes and wonders, and in all of
them amber and jet are represented as attract-
ing chaff; but never a proof from experiments,
never a demonstration do you find in them.
The writers deal only in words that involve in
thicker darkness subject-matter; they treat the
subject esoterically, miracle-mongeringly, ab-
strusely, reconditely, mystically. Hence such
philosophy bears no fruit; for it rests simply on
a few Greek or unusual terms— just as our bar-
bers toss off a few Latin words in the hearing of
the ignorant rabble in token of their learning,
and thus win reputation — bears no fruit, be-
cause few of the philosophers themselves are in-
vestigators, or have any first-hand acquaintance
with things; most of them are indolent and un-
trained, add nothing to knowledge by their
writings, and are blind to the things that might
throw a light upon their reasonings. For not
only do amber and (gagates or) jet, as they sup-
pose, attract light corpuscles (substances): the
same is done by diamond, sapphire, carbuncle,
iris stone, opal, amethyst, vincentina, English
gem (Bristol stone, bristolo), beryl, rock crystal.
Like powers of attracting are possessed by glass,
especially clear, brilliant glass; by artificial gems
made of (paste) glass or rock crystal, antimony
glass, many fluor-spars, and belemnites. Sul-
phur also attracts, and likewise mastich, and
sealing-wax [of lac], hard resin, orpiment (weak-
ly). Feeble power of attraction is also possessed
in favoring dry atmosphere by sal gemma [na-
tive chloride of sodium], mica, rock alum. This
we may observe when in mid-winter the atmos-
phere is very cold, clear, and thin; when the
electrical effluvia of the earth offer less impedi-
ment, and electric bodies are harder: of all this
later. These several bodies (electrics) not only
draw to themselves straws and chaff, but all
metals, wood, leaves, stones, earths, even water
and oil; in short, whatever things appeal to our
senses or are solid: yet we are told that it at-
tracts nothing but chaff and twigs. Hence Alex-
ander Aphrodiseus incorrectly declares the
question of amber to be unsolvable, because
that amber does attract chaff, yet not the leaves
of basil; but such stories are false, disgracefully
inaccurate. Now in order clearly to understand
by experience how such attraction takes place,
and what those substances may be that so at-
tract other bodies (and in the case of many of
these electrical substances, though the bodies
influenced by them lean toward them, yet be-
cause of the feebleness of the attraction they
are not drawn clean up to them, but are easily
WILLIAM GILBERT
made to rise), make yourself a rota ting-needle
(electroscope — versorium) of any sort of metal,
three or four fingers long, pretty light, and
poised on a sharp point after the manner of a
magnetic pointer. Bring near to one end of it a
piece of amber or a gem, lightly rubbed, pol-
ished and shining: at once the instrument re-
volves. Several objects are seen to attract not
only natural objects, but things artificially pre-
pared, or manufactured, or formed by mixture.
Nor is this a rare property possessed by one ob-
ject or two (as is commonly supposed), but evi-
dently belongs to a multitude of objects, both
simple and compound, e.g., sealing-wax and oth-
er unctuous mixtures. But why this inclination
and what these forces, — on which points a few
writers have given a very small amount of in-
formation, while the common run of philoso-
phers give us nothing, — these questions must be
considered fully. Galen recognizes in all three
kinds of attractions in nature: first, the attrac-
tion exercised by those bodies which attract by
an elemental quality— heat, to wit; secondly,
by those which attract by the in-rush into a
vacuum; thirdly, by those which attract
through a property pertaining to their entire
mass: and these three kinds are enumerated by
Avicenna and others. This division cannot by
any means content us, nor does it define the
causes of amber, jet, diamond, and other like
substances, which owe to the same virtue the
forces they possess; nor of loadstone or of other
magnetic bodies, which possess a force altogeth-
er different from that of those other bodies,
both in its efficiency and in the sources whence
it is derived. We must, therefore, find other
causes of movements, or must with these stray
about as it were in darkness, never at all reach-
ing our goal. Now amber does not attract by
heat, for when heated at a fire and brought near
to straws, whether it is merely warm, or wheth-
er it is hot, even burning hot, or even brought
to the flaming point, it has no attraction. Car-
dan (and Pictorius too) is of opinion that the
attraction of amber is much like that seen in the
cupping-glass: yet the attractional force of the
cupping-glass does not really come from igne-
ous force; but he had already said that a dry
body is eager to drink up one that is moist and
juicy, and therefore such bodies are drawn to it.
These two explications are inconsistent, and
they are without ground in reason also. For
were amber to move toward its sustenance, or
other bodies to turn to amber, as to their food,
the one, being swallowed up, would disappear,
while the other would increase in size. And then
why seek in amber the attractive force of fire ?
If fire attracts, why do not many other bodies
heated by the fire, the sun, or by friction at-
tract also? Nor can attraction, because of air
displaced, occur in open air, though this is the
cause Lucretius assigns for magnetic move-
ments; nor in the cupping-glass can heat or fire
feeding on the air attract: the air in the cup-
ping-glass rarefied to flame, when again it be-
comes dense and is compressed into small space,
causes the skin and flesh to rise, because nature
avoids a vacuum. In open air, heated objects
cannot attract, not even metals or stones
brought to a very high temperature by fire. For
an iron rod at white heat, a flame, a candle, a
flaming torch, or a red-hot coal when brought
near to straws or to a revolving pointer (ver-
sorium) does not attract; and yet plainly all
these cause the air to come to them in a cur-
rent, for they consume air as a lamp consumes
oil. But of heat, and how very different is the
view held by the whole crowd of the philoso-
phers, as to its attractive power in natural bod-
ies and materia medica, from the fact as seen in
nature, we will treat elsewhere when we come
to explain what heat and cold really are. They
are very general properties or close appurtenan-
ces of substances, but are not called true causes;
and if I may use the expression, they utter cer-
tain words, but in fact they show nothing spe-
cifically. Nor does the supposed attractive force
of amber arise from any peculiar property of its
substance or from any special relation between
it and other bodies; for in many other substan-
ces, if we but search with any diligence, we see
the same effect, and, by them, all other bodies,
of whatever properties possessed, are attracted.
And likeness is not the cause of amber's attract-
ing, for all things that we see on the globe,
whether similar or dissimilar, are attracted by
amber and such like; hence no strong analogy is
to be drawn either from likeness or from iden-
tity of substance. Besides, like does not attract
like — a stone does not attract a stone, flesh
flesh: there is no attraction outside of the class
of magnetic and electric bodies. Fracastorio
thinks that all bodies that mutually attract are
alike, or of the same species, and that, either in
their action or in their proper subjection: "Now
the proper subjectum" says he, "is that from
which is emitted that emanational something
ON THE LOADSTONE
which attracts, and, in mixed substances, this
is not perceptible on account of deformation,
whereby they are one thing actu> another po-
tentia. Hence, perhaps, hairs and twigs are
drawn to amber and diamond not because they
are hairs, but because there is imprisoned with-
in them either air or some other principle that
is first attracted and that has reference and an-
alogy to that which of itself attracts; and herein
amber and diamond are as one, in virtue of a
principle common to both." So much for Fra-
castorio. But had he in experiment noted that
all bodies are attracted by electrics save those
which are afire or flaming, or extremely rare-
fied, he never would have entertained such
views. Men of acute intelligence, without ac-
tual knowledge of facts, and in the absence of
experiment, easily slip and err. In greater error
are they who hold amber, diamond, etc., and
the objects attracted by them, to be like one
another, but not the same, near to one another
in kind, and that therefore like moves toward
like, and is by it perfected. But that is reckless
speculation; for all bodies are drawn to all elec-
trics, save bodies aflame or too rarefied, as the
air which is the universal effluvium of the globe.
Plants draw moisture, and thus our crops thrive
and grow; but from this analogy Hippocrates in
his book De natura hominis, i, illogically infers
that morbid humour is purged by the specific
virtue of a drug. Of the action of purges we will
treat elsewhere. Wrongly, too, attraction is pos-
tulated to exist in other effects; e.g., when a
stoppered bottle of water being covered with a
heap of wheat, its liquid is drawn out: for in
fact the liquid is reduced to vapour by the spirit
of the fermenting wheat, and the wheat takes in
that vapour. Nor do elephants* tusks suck up
moisture, but transform it into vapour and ab-
sorb it. And thus very many bodies are said to
attract, whereas the ground of their action is to
be sought elsewhere. A large polished lump of
amber attracts; a smaller piece, or a piece of im-
pure amber, seems not to attract without fric-
tion. But very many electric bodies (as pre-
cious stones, etc.) do not attract at all unless they
are first rubbed; while sundry other bodies, and
among them some gems, have no power of at-
traction, and cannot be made to attract, even
by friction; such bodies are emerald, agate, car-
nelian, pearls, jasper, chalcedony, alabaster,
porphyry, coral, the marbles, lapis lydius
(touchstone, basanite), flint, bloodstone, emery
or corundum, bone, ivory; the hardest woods,
as ebony; some other woods, as cedar, juniper,
cypress; metals, as silver, gold, copper, iron.
The loadstone, though it is susceptible of a very
high polish, has not the electric attraction. On
the other hand, many bodies (already men-
tioned) that can be polished attract when rubbed.
All this we shall understand when we have more
closely studied the prime origin of bodies. As
is plain to all, the earth's mass or rather the
earth's framework and its crust consist of a two-
fold matter, a matter, to wit, that is fluid and
humid, and a matter that is firm and dry. From
this twofold matter, or from the simple concre-
tion of one of these matters, come all the bodies
around us, which consist in major proportion
now of terrene matter, anon of watery. Those
that derive their growth mainly from humours,
whether watery humour or one more dense; or
that are fashioned from these humours by sim-
ple concretion, or that were concreted out of
them long ages ago; if they possess sufficient
firmness, and after being polished are rubbed,
and shine after friction, such substances attract
all bodies presented to them in the air, unless
the said bodies be too heavy. For amber and jet
are concretions of water; so too are all shining
gems, as rock-crystal, which is a product of lim-
pid water, not always of such water at an ex-
tremely low temperature, as some have thought,
but sometimes at a more moderate degree of
cold, the nature of the ground fashioning them,
and the humour or juices being prisoned in defi-
nite cavities, just as fluorites are generated in
mines. So clear glass is reduced from sand and
other substances that have their origin in hu-
mid juices. But these substances contain a quan-
tity of impurities of metals, or metals them-
selves, stones, rocks, wood, earth, or are largely
mixed with earth; therefore they do not attract.
Rock crystal, mica, glass, and other electric
bodies do not attract if they be burned or high-
ly heated, for their primordial humour is destroy-
ed by the heat, is altered, and discharged as va-
pour. Hence all bodies that derive their origin
principally from humours, and that are firmly
concreted, and that retain the appearance and
property of fluid in a firm, solid mass, attract all
substances, whether humid or dry. Such as are
parts of the true substance of the earth or differ
but little from that, appear to attract also, but
in a very different way, and, so to speak, mag-
netically: of them we are to treat later. But
those that consist of mixed water and earth, and
that result from equal degradation of both ele-
ments— in which the magnetic force of the
earth is degraded and lies in abeyance, while
the aqueous humour, spoilt by combination with
a quantity of earth, does not form a concretion
WILLIAM GILBERT
by itself, but mingles with the earthy matter-
such bodies are powerless to attract to them-
selves aught that they are not in actual con-
tact with, or to repel the same. For this reason
it is that neither metals, marbles, flints, woods,
grasses, flesh, nor various other substances can
attract or solicit a body, whether magnetically
or electrically (for it pleases us to call electric
force that force which has its origin in hu-
mours). But bodies consisting mostly of hu-
mour and not firmly compacted by nature
wherefore they do not stand friction, but ei-
ther fall to pieces or grow soft, or are sticky, as
pitch, soft rosin, camphor, galbanum, ammoni-
acum, storax, asa, gum benjamin, asphaltum
(especially in a warm atmosphere), do not at-
tract corpuscles. For without friction few bodies
give out their true natural electric emanation
and effluvium. Turpentine resin in the liquid
state does not attract, because it cannot be
rubbed; but when it hardens to a mastic it does
attract.
And now, at last, we have to see why cor-
puscles are drawn toward substances that de-
rive their origin from water, and by what
manner of force, by what hands, so to
speak, such substances lay hold of matters nigh
them.
In all bodies everywhere are presented two
causes or principles whereby the bodies are
produced, to wit, matter (materia) and form
(forma). Electrical movements come from the
materia, but magnetic from the prime forma;
and these two differ widely from each other and
become unlike— the one ennobled by many vir-
tues, and prepotent; the other lowly, of less po-
tency, and confined in certain prisons, as it
were; wherefore its force has to be awakened by
friction till the substance attains a moderate
heat, and gives out an effluvium, and its surface
is made to shine. Moist air blown upon it from
the mouth or a current of humid air from the
atmosphere chokes its powers; and if a sheet of
paper or a linen cloth be interposed there is no
movement. But loadstone, neither rubbed nor
heated, and even though it be drenched with
liquid, and whether in air or water, attracts
magnetic bodies, and that, though solidest bod-
ies or boards, or thick slabs of stone or plates of
metal, stand between. A loadstone attracts only
magnetic bodies; electrics attract everything.
A loadstone lifts great weights; a strong one
weighing two ounces lifts half an ounce or one
ounce. Electrics attract only light weights; e.g.,
a piece of amber three ounces in weight lifts
only one-fourth of a barleycorn's weight.
But this attraction of amber and of electric
bodies must be investigated further; and since
it is an acquired state the question arises why
amber is rubbed, and what state is brought
about by rubbing; also, what causes are evoked
that seize all sorts of substances. By friction it
is made moderately hot and also smooth; and
these conditions must in most cases concur; but
a large polished piece of amber or of jet attracts
even without friction, though not strongly; yet
if it be carefully brought nigh to a flame or a
red coal and warmed to the same degree as by
friction, it does not attract corpuscles, because
it becomes involved in dark fumes from the
body of the hot or flaming mass, which emits a
hot exhalation; and the vapour from that other
body is driven upon it — something quite alien
to the nature of the amber. Besides, the exhala-
tion produced in the amber by an alien heat is
feeble, for the amber must not have any heat
save that produced by friction: its own heat, so
to speak, — not heat contributed by other bod-
ies. For as the igneous heat emitted by any
flaming matter is useless to procure for electrics
their virtue, so, too, heat from the sun's rays
does not excite an electric by the right dissolu-
tion of its matter — rather dissipates and con-
sumes it (albeit a body that undergoes friction
and then is exposed to the solar rays retains its
powers longer than it does in shade, because
that in shade effluvia are condensed more and
more quickly) ; further, the sun's heat, height-
ened by means of a burning-glass, imparts no
power to amber, for it dissipates and spoils all
the electric effluvia. Again, flaming sulphur and
burning sealing-wax do not attract, for heat pro-
duced by friction dissolves bodies into effluvia,
and these are consumed by flame. It is impossi-
ble for solid electrics to be resolved into their
effluvia otherwise than by attrition, save a few
that, because of their native strength, emit ef-
fluvia continually. They are to be rubbed with
bodies that do not foul the surface, and that
cause them to shine, e.g., strong silk, and coarse
woollen cloth, scrupulously clean, and the dry
palm of the hand. Amber may be rubbed with
amber, with diamond, with glass, etc. Thus are
electrics made ready for action.
And now what is it that produces the move-
ment ? The body itself circumscribed by its con-
tour? Or is it something imperceptible for us
flowing out of the substance into the ambient
air? (This appears to have been in some sense
the opinion of Plutarch, who, in the Quaestiones
Platonicae, says that there is in amber something
flame-like, or having the nature of the breath,
ON THE LOADSTONE
and that this, when the paths are cleared by
friction of the surface, is emitted and attracts
bodies.) And if it is an effluvium, does the efflu-
vium set the air in current, and is the current
then followed by the bodies ? or is it the bodies
themselves directly that are drawn up? But if
the amber attracts the body itself, then suppos-
ing its surface is clean and free from adhesions,
what need is there of friction? Nor does the
force come from the lustre proceeding from the
rubbed and polished electric; for the vincentina,
the diamond, and pure glass attract when they
are rough, but not so strongly nor so readily;
because then they are not so easily cleansed of
extraneous moisture settled on the surface, nor
are they subjected all over to such an equal de-
gree of friction as to be resolved into effluvia.
Nor does the sun, with its shining and its rays,
which are of vast importance in nature, attract
bodies thus; and yet the common run of phi-
losophizers think that liquids are attracted by
the sun, whereas only the denser humours are
resolved into rarer, (and) into vapour and air;
and thus, through the motion given to them by
diffusion, they ascend to the upper regions, or,
being attenuated exhalations, are lifted by the
heavier air. Neither does it seem that the elec-
tric attraction is produced by the effluvia rare-
fying the air so that bodies, impelled by the
denser air, are made to move toward the source
of the rarefaction: if that were so, then hot bod-
ies and flaming bodies would also attract other
bodies; but no lightest straw, no rotating point-
er is drawn toward a flame. If there is afflux
and appulsion of air, how can a minute diamond
of the size of a chick-pea pull to itself so much
air as to sweep in a corpuscle of relatively con-
siderable length, the air being pulled toward
the diamond only from around a small part of
one or other end ? Besides, the attracted body
must stand still or move more slowly before
coming into contact, especially if the attract-
ing body be a broad flat piece of amber, on ac-
count of the heaping up of air on the surface,
and its rebounding after collision. And if the
effluvia go out rare and return dense (as with
vapours), then the body would begin to move
toward the electric a little after the beginning
of its application; yet, when rubbed electrics
are suddenly applied to a versorium, instantly
the pointer turns, and the nearer it is to the elec-
tric the quicker is the attraction. But if rare ef-
fluvia rarefy the medium, and therefore the
bodies pass from a denser into a rarer medium,
then the bodies might be attracted sideways or
downward, but not upward, or the attraction
and holding of the bodies would be only for a
moment. But jet and amber after one friction
strongly and for a length of time solicit and at-
tract bodies, sometimes for as long as five min-
utes, especially if the weather is fair. But if the
mass of amber be large, and its surface polished,
it attracts without friction. Flint, on being
struck, gives off inflammable matter that turns
to sparks and heat. Hence the denser fire-con-
taining effluvia of flint are very different indeed
from the electrical effluvia, which, by reason of
their extreme tenuity, cannot take fire, nor are
they fit matter of flame. They are not a breath,
for, when given forth, they do not exert pro-
pelling force; they flow forth without any per-
ceptible resistance, and reach bodies. They are
exceedingly attenuated humours, much more
rarefied than the ambient air; to produce them
requires bodies genera ted of humour and consol-
idated to considerable hardness. Non-electric
bodies are not resolvable into humid effluvia;
and such effluvia mingle with the common and
general effluvia of the earth, and are not pecu-
liar. In addition to the attracting of bodies, elec-
trics hold them for a considerable time. Hence
it is probable that amber exhales something pe-
culiar that attracts the bodies themselves, and
not the air. It plainly attracts the body itself in
the case of a spherical drop of water standing on
a dry surface; for a piece of amber held at suit-
able distance pulls toward itself the nearest par-
ticles and draws them up into a cone; were they
drawn by the air the whole drop would come
toward the amber. And that amber does not at-
tract the air is thus proved: take a very slender
wax candle giving a very small clear flame;
bring a broad flat piece of amber or jet, careful-
ly prepared and rubbed thoroughly, within a
couple of fingers' distance from it ; now an am-
ber that will attract bodies from a considerable
radius will cause no motion in the flame, though
such motion would be inevitable if the air were
moving, for the flame would follow the current
of air. The amber attracts from as far as the ef-
fluvia are sent out; but as the body comes near-
er the amber its motion is quickened, the forces
pulling it being stronger, as is the case also in
magnetic bodies, and in all natural motion; and
the motion is not due to rarefaction of the air
or to an action of the air impelling the body to
take the vacated place; for in that case the body
would be pulled but not held, since, at first, ap-
proaching bodies would even be repelled just
as the air itself would be: yet in fact the air is not
in the least repelled even at the instant that the
rubbed amber is brought near after very rapid
WILLIAM GILBERT
friction. An effluvium is exhaled by the am-
ber and is sent forth by friction; pearls, carneli-
an, agate, jasper, chalcedony, coral, metals, and
the like, when rubbed are inactive; but is there
nought that is emitted from them also by heat
and friction? There is indeed; but what is emit-
ted from the denser bodies, and those with con-
siderable admixture of earth matter, is thick
and vaporous; and in fact in the case of very
many of the electric bodies, if they be violently
rubbed, there is but a faint attraction of bodies
to them, or none at all; the best method is to
use gentle but very rapid friction, for so the fin-
est effluvia are elicited. The effluvia arise from
a subtle solution of moisture, not from force ap-
plied violently and recklessly; this is true espec-
ially of bodies that are of oily substance consol-
idated, which, when the atmosphere is thin and
the wind is from the north, or here in England
from the east, produce their effects best and
with most certainty; but in a south wind and a
humid atmosphere the effect is very slight: so
that effluvia that attract but feebly when the
weather is clear, produce no motion at all when
it is cloudy. And this as well because in thick
weather light objects are harder to move, as also
(and rather) because the effluvia are stifled, and
the surface of the rubbed body is affected by the
vaporous air, and the effluvia are stopped at
their very origin; hence it is that in amber, jet,
and sulphur, because these bodies do not so
readily collect the humid air on their surface,
and are much more thoroughly resolved, this
force is not so easily suppressed as in gems, rock-
crystal, glass, and the like, which collect the
condensed moist air on their surface. But the
question may arise, why amber attracts water,
though water existing on a surface annuls its
action. That is because it is one thing to sup-
press the effluvium at its rise, another to destroy
it after it is emitted. Thus a certain gauzy tex-
ture of silk, commonly called sarsenet ', when
quickly laid over amber immediately after fric-
tion, hinders the body's attraction; but if it be
interposed midway between the two bodies, it
does not altogether annul the attraction. Mois-
ture from steam, a breath from the mouth,
water thrown on the amber, instantly check the
effluvium. But olive-oil that is light and pure
does not prevent it, and even rubbing amber
with a warm finger dipped in the oil does not
prevent attraction. But if after that friction the
amber be drenched with alcohol, or brandy, it
does not attract, as the spirit is heavier, denser,
than the oil, and when added to the oil sinks
below it. For olive-oil is light and rare, and does
not oppose the passage of the lightest effluvia.
A breath, then, proceeding from a body that is
a concretion of moisture or aqueous fluid, reach-
es the body that is to be attracted, and as soon
as it is reached it is united to the attracting elec-
tric; and a body in touch with another body by
the peculiar radiation of effluvia makes of the
two one: united, the two come into most inti-
mate harmony, and that is what is meant by
attraction. This unity is, according to Pytha-
goras, the principle, through participation, in
which a thing is said to be one. For as no action
can be performed by matter save by contact,
these electric bodies do not appear to touch,
but of necessity something is given out from
the one to the other to come into close contact
therewith, and be a cause of incitation to it.
All bodies are united and, as it were, cement-
ed together by moisture,and hence a wet body
on touching another body attracts it if the other
body be small; and wet bodies on the surface of
water attract wet bodies. But the peculiar
effluvia of electrics, being the subtilest matter of
solute moisture, attract corpuscles. Air, too (the
earth's universal effluvium), unites parts that
are separated, and the earth, by means of the
air, brings back bodies to itself; else bodies
would not so eagerly seek the earth from heights.
The electric effluvia differ much from air, and
as air is the earth's effluvium, so electric bodies
have their own distinctive effluvia; and each pe-
culiar effluvium has its own individual power
of leading to union, its own movement to its
origin, to its fount, and to the body that emits
the effluvium. But bodies that give out a thick
or a vaporous or an aerial effluvium when rubbed
have no effect; for either such effluvia are
diverse from humour (unifier of all things), or,
being very like the common air, they become
blended with the air and one with it : wherefore
they have no effect in the air, and do not produce
any movements different from those of that uni-
versal and common element. Bodies tend to
come together and move about on the surface
of water like the rod C, which dips a little into
the water. Evidently the rod EF, floated by the
cork H and having only the wetted end F above
the water's surface, will be attracted by the rod
C, if C be wetted a little above the water's sur-
ON THE LOADSTONE
33
face. As a drop brought into dbntact with an-
other drop is attracted, and the two forthwith
unite, in the same way a wet object on the sur-
face of water seeks union with another wet ob-
ject when the surface of the water rises in both:
at once, like drops or bubbles of water, they
come together; but they are in much nigher
neighborhood than in the case of electrics, and
they unite by their wetted surfaces. But if the
whole rod C be dry above the water, it no longer
attracts but repels the rod EF. The same is seen
in the case of bubbles on water: one is seen to
approach another, all the more rapidly the near-
er they are. Solids draw to solids through the
medium of liquid; e.g., touch the end of a ver-
sorium with the end of a rod on which a drop of
water stands: the instant the rotating pointer
comes in contact with the circumference of the
drop it adheres to it with a sudden motion. So
do bodies concreted from liquids when melted
a little in the air exercise attraction, their efflu-
via being the means of unition; for the water in
humid bodies or in bodies drenched with super-
ficial moisture on the top of water has the force
of an effluvium. A clear atmosphere is a good
medium for the electric effluvium developed
from concreted humour. Wet bodies projecting
out of the surface of water come together, if
they be near, and unite, for the water's surface
rises around wet surfaces. A dry body does not
move toward a wet, nor a wet toward a dry, but
rather they seem to go away from each other;
for if all of the body that is above the water is
dry, the nearest water surface does not rise but
falls away with subsidence of the surface around
the dry object. So, too, a dry body does not run
to the dry rim of a vessel containing water; but,
on the contrary, a wet object does. In the figure,
AB is the water surface; C, D, two rods with
E F
their projecting ends wet. Evidently the sur-
face of the water at Cand D rises simultaneously
with the rods; hence the rod C, because its wa-
ter, standing above the general level, seeks equi-
librium and union, moves with the water to-
ward D. On the wet rod E the water rises also,
but by the dry rod F the water is depressed, and
as it strives to depress also the water rising on E,
the higher water at E turns away from F, for it
refuses to be depressed. All electric attractions
are effected by means of moisture, and thus all
things come together because of humour: fluid
bodies and aqueous bodies come together on the
surface of water, and concreted bodies, if re-
duced to vapour, come together in the air. And
in the air the effluvium of electrics is very rare,
that so it may more thoroughly permeate the
atmosphere, and yet not give it impulsion by
its own motion. For were this effluvium as dense
as air, or the winds, or the fumes of burning
saltpetre, or as the thick, foul effluvia emitted
with much force from other bodies, or as the
air from vaporized water rushing forth from a
pipe (as in the instrument described by Hero of
Alexandria in his book Spiritualid) : in such case
it would repel everything, and not attract. But
those thinner effluvia lay hold of the bodies with
which they unite, enfold them, as it were, in
their arms, and bring them into union with the
electrics; and the bodies are led to the electric
source, the effluvia having greater force the
nearer they are to that. But what is the effluvi-
um from rock-crystal, glass, diamond — substan-
ces very hard and very highly compressed ? For
such effluvium there is no need of any notable
or sensible outflow of substance: no need of
abrading, or rubbing, or otherwise disfiguring
the electric body: odoriferous substances give
forth fragrance for many years, exhale contin-
ually, yet are not soon consumed. Cypress wood,
as long as it remains sound— and it lasts a very
long time— is fragrant, as many learned men
testify from experience. Such an electric, after
only a moment's friction, emits powers subtile
and fine, far beyond all odors; but sometimes
an odor also is emitted by amber, jet, sulphur,
these bodies being more readily resolved. Hence
it is that usually they attract after the gentlest
friction, or even without friction; and they at-
tract more powerfully and keep hold longer be-
cause their effluvia are stronger and more last-
ing. But diamond, glass, rock-crystal, and very
many of the harder and more compacted gems
are heated, and then rubbed for a good while at
first, after which they, too, attract strongly:
they cannot be resolved in any other way. Elec-
trics attract all things save flame and objects
aflame, and thinnest air. And as they do not
draw to themselves flame, so they have no effect
on a versorium if it have very near it on any side
the flame of a lamp or of any burning substance;
for it is plain that the effluvia are consumed by
flame and igneous heat. Therefore electrics do
not attract either flame or bodies near flame; for
such effluvia have the virtue and analogy of
rarefied humour, and they will produce their
effect, bringing about unition and continuity,
34
WILLIAM GILBERT
not through the external action of humours, or
through heat, or through attenuation of heated
bodies, but through the attenuation of the hu-
mid substance into its own specific effluvia. Yet
they draw to themselves the smoke from an ex-
tinguished candle; and the lighter the smoke be-
comes as it ascends, the less strongly is it attract-
ed, for substances that are too rare do not suf-
fer attraction. At last, when the smoke has near-
ly vanished, it is not attracted at all, as is plain-
ly seen when the fact is observed toward the
light. But when it has passed quite into the air
it is not stirred by electrics, as has already been
shown. For thin air itself is in no wise attracted,
save by reason of its coming into a vacuum, as
is seen in furnaces in which air is supplied by
means of appliances for drawing it in. Therefore
the effluvium called forth by a friction that does
not clog the surface — an effluvium not altered
by heat, but which is the natural product of the
electric body — causes unition and cohesion,
seizure of the other body, and its confluence to
the electrical source, provided the body to be
drawn is not unsuitable by reason either of the
circumstances of the bodies or of its own weight.
Hence corpuscles are carried to the electrical
bodies themselves. The effluvia spread in all di-
rections: they are specific and peculiar, and sui
generis, different from the common air; gener-
ated from humour; called forth by calorific mo-
tion and rubbing, and attenuation; they are as
it were material rods— hold and take up straws,
chaff, twigs, till their force is spent or vanishes;
and then these small bodies, being set free again,
are attracted by the earth itself and fall to the
ground. The difference (distinction) between
electric and magnetic bodies is this: all magnet-
ic bodies come together by their joint forces
(mutual strength); electric bodies attract the
electric only, and the body attracted under-
goes no modification through its own native
force, but is drawn freely under impulsion in the
ratio of its matter (composition). Bodies are at-
tracted to electrics in a right line toward the
centre of electricity: a loadstone approaches
another loadstone on a line perpendicular to
the circumference only at the poles, elsewhere
obliquely and transversely, and adheres at the
same angles. The electric motion is the motion
of coacervation of matter; the magnetic is that
of arrangement and order. The matter of the
earth's globe is brought together and held to-
gether by itself electrically. The earth's globe
is directed and revolves magnetically; it both
coheres and, to the end it may be solid, is in its
interior fast joined.
CHAPTER 3. Opinions of others concerning magnetic
coition^ which they call attraction
HAVING treated of electrics, we have now to set
forth the causes of magnetic coition. Coition,
we say, not attraction, for the term attraction
has wrongfully crept into magnetic philosophy,
through the ignorance of the ancients; for where
attraction exists, there, force seems to be brought
in and a tyrannical violence rules. Hence, if we
have at any time spoken of magnetic attraction,
what we meant was magnetic coition and pri-
mary confluence. But here it will be not un-
profitable first to set forth briefly the views of
others, both among the ancients and the mod-
erns. Orpheus, in his hymns, tells that iron is
drawn by the loadstone as the bride to the em-
braces of her spouse. Epicurus holds that iron
is drawn by the loadstone as straws by amber;
and adds a reason: "Atoms," he says, "and in-
divisible bodies that flow" from stone and from
iron, agree together in their figures, so that they
readily embrace mutually; hence, when they
impinge on concretions both of iron and stone,
they rebound into the middle space, connected
together on the way, and carry the iron with
them/' This, surely, cannot be, for though solid
and very dense bodies, or blocks of marble,
stand between, they do not hinder the passage
of this potency, though they can separate atoms
from atoms; besides, on the hypothesis, the
stone and iron would quickly be resolved into
atoms, so profuse and incessant would be the
atomic outflow. And as the mode of attraction
is quite different in amber, there the Epicurean
atoms cannot agree in their figures. Thales, as
we are told by Aristotle, in Book i, On the Soul,
deemed the loadstone endowed with a sort of
life, because it possesses the power of moving
and attracting iron. Anaxagoras was of the same
opinion. The opinion of Plato in the Timasus,
about the effect of the Herculean stone, is base-
less. He says: "With respect to all the motions
of water, the fallings of thunder, and the won-
derful circumstances observed in the attraction
of amber, and the Herculean stone— in all these,
no real attraction takes place at all, but, as a
vacuum can nowhere be found, the particles
are mutually impelled by each other; hence, as
they all individually, both in a separate and
mingled state, have an attraction for their own
proper seats, it is by the mutual intermingling
of these affections, that such admirable effects
present themselves to the view of the accurate
investigator." Galen knows not why Plato
should have chosen rather the theory of cir*
ON THE LOADSTONE
35
cumpulsion than of attraction (on this point
alone differing from Hippocrates), seeing that
circumpulsion harmonizes in fact neither with
reason nor with experiment. For neither is air
nor anything else circumpelled, and even the
bodies that are attracted are not borne to the
attracting body in confused fashion or in a cir-
cle. The Epicurean poet Lucretius thus presents
his master's theory:
Principle fluere e lapide hocpermulta necesset
Semina sive aestum, qui discutit aera plagis;
Inter qui lapidem, ferrumque est, cumque locatus,
Hoc ubi inanitur spatium, multiusque vacefit
In media locus: extemplo primordia ferri
In vacuum prolapsa cadunt coniuncta\ fit ut qui
Anulus ipse sequatur, eatque ita corpore toto, etc.1
A similar explication is offered by Plutarch in
the Quxstiones Platonicx. He says that the load-
stone emits heavy exhalations, whereby the
contiguous air, being impelled, makes dense the
air in front of it, and that air, driven round in a
circle and returning to the part whence the air
was displaced, forcibly carries the iron with it.
The following theory of the powers of loadstone
and amber is propounded by Joannes Costaeus
of Lodi: Costaeus holds that "there is work on
both sides, result on both sides, and therefore
the motion is produced in part by the load-
stone's attraction, in part by the iron's spontan-
eous movement; for, as we say that the vapours
given out by the loadstone do by their own na-
ture haste to attract the iron, so, too, do we say
that the air impelled by the vapours, while
seeking a place for itself, is turned back, and
when turned back impels and transfers the Iron,
which is picked up, as it were, by it, and which,
besides, is exerted on its own account. In this
way there is found a certain composite move-
ment, resulting from the attraction, the spon-
taneous motion, and the impulsion; which com-
posite motion, however, is rightly to be refer-
red to attraction, because the beginning of this
motion is invariably from one term, and its end
is there too; and that is precisely the distin-
guishing character of attraction." There is, it is
true, mutual action, not mutual work; the load-
stone does not thus attract, and there is no im-
Eulsion; neither is the principle of the motion
>und in vapours and their return movements:
that is Epicurus's theory, so oft repeated by
others. Galen errs in his first book, On the Nat-
ural Faculties ', ch. 14, when he expresses the
opinion that whatever agents draw out the ven-
om of serpents or arrows possess the same pow-
ers as the loadstone. As for this attraction (if
1 See On the Nature of Things, vi. 1002-8.
attraction it may be called) of medicaments,
we will treat of it in another place. Drugs
against poisons and arrow-wounds have no re-
lation, no resemblance, to the actions of mag-
netic bodies. Galen's followers, who teach that
purgative medicines attract because of likeness
of substance, say that bodies are attracted on
account of resemblance, not of identity; there-
fore, say they, loadstone draws iron, but iron
does not draw loadstone. But we say and prove
that this takes place in all prime bodies, and in
bodies that are allied and especially that are
near akin to these, and this on account of iden-
tity: wherefore loadstone draws loadstone, and
iron draws iron; all true earth substance draws
its kind; and iron invigorated by the action of a
loadstone within whose sphere of influence it is,
draws iron more powerfully than it does load-
stone. Cardan asks why no other metal is drawn
by any stone; and his answer is, because no oth-
er metal is so cold as iron: as if, forsooth, cold
were cause of attraction, or iron were much
colder than lead, which neither follows the load-
stone nor (leans toward it. But this is sorry tri-
fling, no better than old wives' gossip. Of the
same sort is the belief that the loadstone is a
living thing, and that iron is its victual. But how
does loadstone feed on iron if the iron filings it
is kept in neither are consumed nor become
lighter in weight? Cornelius Gemma (Cosmo-
crit, x), declares that loadstone draws iron to it-
self by .neans of invisible rods; and to this opin-
ion he tacks on a story of the sucking-fish and
the catablepas. Guilelmus Puteanus deduces the
power of the loadstone, not from a property of
its whole substance unknown to any one and in-
capable of demonstration (as Galen held, and
after him nearly all physicians), but from "its
substantial form as from a prime motor and self-
motor, and as from its own most potent nature
and its natural temperament, as the instrument
which the efficient form of its substance, or the
second cause, which is without a medium, em-
ploys in its operations. So the loadstone attracts
iron not without a physical cause, and for the
sake of some good." But nothing like this is
done in other bodies by any substantial form un-
less it be the primary one, and this Puteanus
does not recognize. Naught but good is assured-
ly held out to the loadstone, to be got from the
appulsion of the iron (a sort of friendly associa-
tion), ye.t the temperament of which he speaks
is not to be found, cannot even be imagined as
something that is to be the instrument of the
form. For of what use can temperament be in
magnetic movements that are calculable, defi-
WILLIAM GILBERT
nite, constant, comparable to the movements
of the stars; at great distance, with thick, dense
bodies interposed. In Baptista Porta's opinion,
the loadstone seems to be a mixture of stone and
iron, i.e., ferruginous stone, or stony iron. "The
stone," he says, "is not changed into iron so as
to lose its own nature, nor is the iron so merged
in the stone but that it retains its own essence;
and while each strives to overcome each, from
the struggle results attraction of the iron. In the
mass (of the loadstone) there is more stone than
iron; therefore the iron, lest it should be depen-
dent on (subdued by) the stone, craves the
strength and company of iron, to the end that
what it cannot procure of itself it may obtain
by the help of the other The loadstone does
not attract stones because it has no need of them
there being stone enough in its mass; and if one
loadstone attracts another that is not for the
sake of the stone, but of the iron shut up in the
stone." As though the iron in a loadstone were
a distinct body and not one blended with an-
other, like all other metals in their ores. And it
is height of absurdity to speak of these substan-
ces, thus confounded together, as warring with
each other and quarreling, and calling out from
the battle for forces to come to their aid. Now,
iron itself when touched with loadstone seizes
iron with not less force than loadstone itself.
These fights, seditions, conspiracies, in a stone,
as though it were nursing quarrels as an occasion
for calling in auxiliary forces, are the maunder-
ings of a babbling hag, rather than the devices
of an accomplished prestigiator. Others have
thought that the cause is a sympathy. But even
were fellow-feeling there, even so, fellow-feeling
is not a cause; for no passion can rightly be said
to be an efficient cause. Others again assign as
the cause likeness of substance, and still others
postulate rods (radii) imperceptible to the senses.
These, in very many ways, make a sad misuse of
a term first employed by mathematicians. In
more scholarly fashion, Scaliger declares that
iron moves to the loadstone as to its mother's
womb, there to be perfected with recondite
principles, as the earth tends to the centre. The
godlike Thomas,1 in Book vn of his Physica,
treating of the causes of motion, says: "A thing
can in another sense be said to pull, in that it
moves (an object) toward itself, by altering it
in any way, by which alteration it comes about
that the body altered moves with respect to
place; and in this way is the loadstone said to
draw iron : for as a generant moves heavy things
and light in so far as it gives them the form
1 Thomas Aquinas.
whereby they are moved to a place; so does the
loadstone give to iron some quality through
which it is moved to the loadstone." This view,
one by no means ill-conceived, this most learned
man, proceeds later briefly to corroborate, cit-
ing incredible accounts of the loadstone and of
the power of garlic over the loadstone.
Nor is what Cardinal de Cusa states to be dis-
regarded. Says he: "Iron hath in the loadstone
a certain principle of its efflux, and while the
loadstone by its presence excites the heavy and
ponderous iron, the iron is, by a wonderful
longing, raised above the natural motion (where-
by it ought to tend downward according to its
weight), and moves upward, uniting in its prin-
ciple. For were there not in iron some natural
foretaste of the loadstone, it would no more
move toward that than toward any other stone;
and were there not in the loadstone a stronger
inclination toward iron than toward copper,
that attraction would not exist." Such, as pro-
pounded by different writers, are current opin-
ions about the attraction of the loadstone, all
of them full of doubt and uncertainty. As for
the causes of magnetic movements, referred to
in the schools of philosophers to the four ele-
ments and to prime qualities, these we leave for
roaches and moths to prey upon.
CHAPTER 4. Of the strength of a loadstone and its
form: the cause of coition
QUITTING the opinions of others about the at-
traction of the loadstone, we will now show the
reason of its coition and the nature of its mo-
tion. There are two kinds of bodies that are
seen to attract bodies by motions perceptible
to our senses — electric bodies, and magnetic.
Electrical bodies do this by means of natural
effluvia from humour; magnetic bodies by for-
mal efficiencies or rather by primary native
strength (vigor). This form is unique and pe-
culiar: it is not what the Peripatetics call causa
formalis and causa specifica in mixtis and secunda
forma; nor is it causa propagatrix generantium
corporum; but it is the form of the prime and
principal globes; and it is of the homogeneous
and not altered parts thereof, the proper entity
and existence which we may call the primary,
radical, and astral form; not Aristotle 's prime
form, but that unique form which keeps and
orders its own globe. Such form is in each globe
— the sun, the moon, the stars — one; in earth
also 'tis one, and it is that true magnetic po-
tency which we call the primary energy. Hence
the magnetic nature is proper to the earth and
is implanted in all its real parts according to a
ON THE LOADSTONE
37
primal and admirable proportion. It is not de-
rived from the heavens as a whole, neither is it
generated thereby through sympathy, or in-
fluence, or other occult qualities: neither is it
derived from any special star; for there is in the
earth a magnetic strength or energy of its own,
as sun and moon have each its own forma; and
a little fragment of the moon arranges itself, in
accordance with lunar laws, so as to conform to
the moon's contour and form, or a fragment of
the sun to the contour and form of the sun,
just as a loadstone does to the earth or to an-
other loadstone, tending naturally toward it and
soliciting it. Thus we have to treat of the earth,
which is a magnetic body, a loadstone; then,
too, of its true, native parts, which are magnet-
ic, and of how they are affected by coition.
A body that is attracted by a magnetic body
is not by it altered, but remains unimpaired and
unchanged as it was before, neither has it now
greater virtue. A loadstone draws magnetic bod-
ies, and they from its energy eagerly draw for-
ces not in their extremities only, but in their
inmost parts. For an iron rod held in the hand
is magnetized in the end where it is grasped, and
the magnetic force travels to the other extrem-
ity, not along the surface only, but through the
inside, through the middle. Electrical bodies
have material, corporeal effluvia. Is any magnet-
ic effluvium emitted, corporeal or incorporeal ?
Or is nothing at all that subsists emitted ? But if
the effluvium is a body, it must needs be light
and spiritual so as to enter the iron. Is it such
as is exhaled from lead when quicksilver, which
is liquid and fluid, is by the mere odour and vap-
our of lead solidified, and remains as a strongly
coherent metal ? Gold too, which is very solid
and dense, is reduced to a powder by the thin
vapour of lead. Can it be that as quicksilver can
enter gold, so the magnetic odour can enter the
substance of iron, changing it by its substantial
property, though in the bodies themselves there
is no change perceptible by our senses? For
without such entering a body is not changed
by another body, as the chemists, not without
reason, do teach. But if these effects were pro-
duced by a material entrance, then were resist-
ant, dense bodies interposed between such bod-
ies; or were the magnetic bodies shut up in the
middle of very thick, dense bodies, objects of
iron would not be acted on by the loadstone.
Nevertheless, these two do strive to come to-
gether and are changed. Therefore the magnetic
forces have no such conception, no such origin,
as this: nor are they due to those most minute
par tides of loadstone imagined by Baptista Porta
concentrated as it were into hairs, and springing
from friction of the loadstone, which parts fast-
ening on to the iron give it the magnetic powers.
For the electric effluvia, as they are hindered by
the interposition of any dense body, so too are
unable to attract through a flame, or if a flame be
near by. But iron, which is hindered by no ob-
stacle (from) deriving from the loadstone force
and motion, passes through the midst of a flame
to join the loadstone. Take a short piece of iron
wire, and when you have brought it near to a
loadstone it will make its way through the
flames to the stone; and a needle turns no less
rapidly, no less eagerly, to the loadstone though
a flame intervenes than if only air stands be-
tween. Hence a flame interposed does not pre-
vent coition. But were the iron itself red-hot,
it certainly would not be attracted. Apply a
red-hot iron rod to a magnetized needle and the
needle stands still, not turning to the iron; but
as soon as the temperature has fallen somewhat
it at once turns to it. A piece of iron that has
been magnetized, if placed in a hot fire until it
becomes red-hot, and permitted to remain fora
little while, loses the magnetic power. Even
loadstone itself loses its native and inborn pow-
ers of attracting, and all other magnetic prop-
erties, if left long in fire. And though some mag-
netic ores when roasted exhale a deep- blue or
sulphurous and foul-smelling vapour, neverthe-
less such vapour is not the soul of the loadstone;
neither is it the cause of the attraction of iron,
as Porta supposes.1 Nor do all loadstones when
roasted or burned smell of sulphur or give out
sulphur fumes: that property is something add-
ed, a sort of congenital evil which comes from
the foul bed or matrix in which the loadstone
is produced; nor does the material corporeal
cause introduce into the iron anything of the
same sort, for iron derives from loadstone the
power of attracting and the property of verti-
city, though glass or gold or another sort of
stone stand between, as later, when treating of
the magnetic direction, we shall clearly prove.
But fire destroys in the loadstone the magnetic
qualities, not because it plucks out of it any
particular attractional particles, but because
the quick, penetrating force of the flame de-
forms it by breaking its matter up; just as in
the human body the soul's primary powers are
not burnt, though yet the burnt body remains
without faculties. But though the iron remains
after perfect ignition, and is not converted into
either ash or slag; still, as Cardan not injudi-
ciously remarks, red-hot iron is not iron, but
1 Natural Magic, vn, 2.
WILLIAM GILBERT
something lying outside its own nature, until
it returns to itself. For just as, by the cold of
the ambient air, water is changed from its own
nature into ice, so iron made white-hot by fire
has a confused, disordered form, and therefore is
not attracted by a loadstone, and even loses its
power of attracting, however acquired; it also
acquires a different verticity when, as though
born anew, it is impregnated by a loadstone or
the earth; in other words, when its form, not
utterly destroyed, yet confused, is restored. I
shall have more to say on this subject when
treating of changed verticity (Book in. 10).
Hence, Fracastorio finds no confirmation of his
opinion that the iron is not altered: "For," says
he, "if it were altered by the loadstone's form,
the form of the iron would be spoiled." Yet this
alteration is not generation, but restitution and
re-formation of a confused form.
Hence that is not corporeal which emanates
from the loadstone, or which enters the iron, or
which is given forth again by the awakened
iron; but one loadstone gives portion to another
loadstone by its primary form. And a loadstone
recalls the cognate substance, iron, to formate
energy and gives it position: hence does it leap
to the loadstone and eagerly conforms thereto
(the forces of both harmoniously working to
bring them together); for the coition is not in-
determinate and confused, it is not a violent in-
clination of body to body, not a mad chance
confluence. Here no violence is offered to bod-
ies, there are no strifes or discords; but here we
have, as the condition of the world holding to-
gether, a concerted action — to wit, an accord-
ance of the perfect, homogeneous parts of the
world's globes with the whole, a mutual agree-
ment of the chief forces therein for soundness,
continuity, position, direction, and unity. In
view of this so wonderful effect, this stupendous
innate energy — an energy (strength) not exist-
ing in other elements — the opinion of Thales
the Milesian is, in Scaliger's judgment, not ut-
terly absurd, not a lunatic's fancy. Thales as-
cribed to the loadstone a soul, for it is incited,
directed, and moved in a circle by a force that
is entire in the whole and entire in each part,
as later will appear, and because it seems most
nearly to resemble a soul. For the power of self-
movement seems to betoken a soul, and the
supernal bodies, which we call celestial, as it
were divine, are by some regarded as animated
because that they move with wondrous regu-
larity. If two loadstones be set over against each
other in their floats on the surface of water,
they do not come together forthwith, but first
they wheel round, or the smaller obeys the larg-
er and takes a sort of circular motion; at length,
when they are in their natural position they
come together, In iron that has not been excited
by the loadstone, there is no need of these pre-
liminaries; for iron, though made from the fin-
est loadstone, has no verticity save such as it
gets by chance and momentarily; and this is not
stable nor fixed, for while it ran liquid in the
furnace its parts were thrown into confusion.
Such a body instantly receives from the pres-
ence of the loadstone verticity and natural con-
formity to it, being powerfully altered and con-
verted, and absolutely metamorphosed into a
perfect magnet: so, like an actual part of the
loadstone, it flies to it. For there is naught that
the best loadstone can do which cannot be done
by iron excited by a loadstone— not magnet-
ized at all, but only placed in the neighbour-
hood of a loadstone. For as soon as it comes with-
in the loadstone's sphere of influence, though
it be at some distance from the loadstone it-
self, the iron changes instantly, and has its form
renewed, which before was dormant and inert,
but now is quick and active: all this will appear
clearly when we come to present the proofs of
magnetic direction (in Book in). Thus the mag-
netic coition is the act of the loadstone and of
the iron, not of one of them alone: it is &re\ex'
eta, not tpyov\ it is awei/reXexeia and conactus
(mutual action) rather than sympathy. There is,
properly speaking, no magnetic antipathy; for
the flight and turning away of the poles and the
wheeling around of the whole is the act of each
of the two toward unition, resulting from the
avv€vr€\ex^a and conactus1 of both. Thus the
iron puts on anew its form; and because that is
awakened, as also in order more surely to gain
its form, it rushes headlong on the loadstone, and
not with circlings and wheelings, as in the case of
two loadstones. For as, long ages ago, nay at the
very beginning of things, there were gendered
in the loadstone and therein fixed verticity and
the power of coordinating; and since the great
mastering form of the earthly globe cannot be
readily changed by another magnet, as iron is
changed, therefore, the nature of each being
constant, neither hath the momentary power
of altering the verticity of the other, but the
two do but come to agreement with each other.
And magnetized iron, in case it is unable for
whatever reason to cause the piece of iron in
the natural state to turn, as does the pointer
of a versorium, is itself seized at either end by
1 Conactus, i>., combined or mutual action. See Book
v, 12.
ON THE LOADSTONE
a loadstone brought nigh it. For the loadstone,
as it imparts so can it alter verticity, and it can
in an instant bestow the formal energy in either
end. Thus iron may be transformed variously,
as that form is adventitious and has not yet
abided long in the metal. In iron, because its
body is fused when a magnetic or a ferruginous
ore is smelted, the virtue of the primal form,
which previously existed distinct, is now con-
fused; but a sound loadstone, when brought
near, sets up again the primal action: the form,
now arranged and ordered again, joins forces
with the loadstone, and, each with other, the
two come to agreement, after the manner of the
loadstone, in all their movements toward union;
they enter into alliance, and whether joined
by bodily contact or standing within their
sphere of influence, are one and the same. For
when iron is reduced in the furnace from its
ore, or when steel is got from its ore, which is
loadstone, the metallic matter is melted and be-
comes fluid, and the iron and the steel run off,
leaving their slag: this slag consists of matter
spoilt by the intense heat of the fire, or of use-
less matter, or of dross, due to some imperfec-
tion or to some intermixture in the projecting
surface of the earth. Thus the iron or steel is a
purified material, wherein the metallic element,
all disordered by the smelting (for the forces of
that primal form are all confused and unset-
tled), is brought back again, as it were, to life,
to normal form, and to completeness. Its mat-
ter is thus awakened, and tends to union, which
is the bond of the universe and the necessary
condition of the conservation of all things.
For this reason, and because of the purging
of the ore and its change into a purer body, the
loadstone gives to iron greater power of attract-
ing than exists in itself. For if you put some
iron-filings or a nail on a large magnet, a piece
of iron joined to the magnet steals the filings
and the nail, and holds them as long as it re-
mains alongside the magnet: so, too, iron at-
tracts iron more powerfully than does a load-
stone, if the iron be afformed, and remain with-
in the sphere of the form given out to it. Again,
a piece of iron nicely adjusted to the pole of a
loadstone holds a greater weight than the load-
stone does. So, then, iron and steel are the
better elements of their ores, purified by the
action of fire, and the loadstone impregnates
them again with their forms; wherefore to it
do they come by spontaneous approach, so soon
as they enter the circle of the magnetic forces,
for by it are they first possessed, and made con-
tinuous, and united with perfect union. Once
39
within that circle they have absolute continu-
ity, and they are joined by reason of their ac-
cordance, albeit the bodies themselves be sep-
arated. For the iron is not, after the manner of
electrics, possessed and pulled by substantial ef-
fluvia, but only by the immaterial act of the
form or by its incorporeal going forth, which as
in a continuous and homogeneous body doth
act in the iron subjectum, and is received into
it; nor has it need of wider paths.
Hence it is that, with the densest bodies in-
terposed, the iron is put in motion throughout
and is attracted, and that the iron, in presence
of the loadstone thoroughly stirs and attracts
the loadstone itself, and that with their mutual
forces they make that rush toward union which
commonly is called attraction. But these for-
mal forces sally forth and in meeting unite; and
the force conceived in the iron, that also forth-
with has its efflux. But Julius Scaliger, who, in
his 344th disquisition, cites other examples to
prove this explanation to be absurd, is far a-
stray. For the virtues of prime bodies are not
comparable with those that are derivate and
mixed. Were he still among the living, he might
now, in the chapter on "Effused Magnetic
Spherical Forms," discover what is the nature
of effused forms.
But if iron be badly injured by rust it is but
little or not at all affected by the loadstone,
for when the metal is corroded and marred by
external causes or by decay it is spoilt, as has
been said of the loadstone, and loses its prime
qualities that are conjoined to its form, or, the
stone being impaired by age, these qualities are
weak and feeble ; neither can it be duly informed
when once it has suffered decay. But a strong,
fresh loadstone pulls all sound clean iron, and
the iron (having conceived force) powerfully
attracts other iron — as pieces of iron wire, iron
nails; and not only these separately and directly
but one after another, one at the end of another,
thus holding three, four, or five: thus forming
as it were a chain, the successive nails sticking
to one another and suspended from one another.
But the loadstone would not attract the last
piece in such a line if there were no nails in the
mid-space. Thus a loadstone placed at A pulls
B
the nail or bar 5, and, in like manner, after B
pulls C, and after C,D; but at the same distance
does not pull aloft D: that is so for the reason
that when the nails form an unbroken line the
presence of the loadstone A, because of its prop-
WILLIAM GILBERT
er forces, raises the magnetic form of the iron
objects B and C, and makes them as it were its
auxiliary forces, while B and C, like a continu-
ous magnetic body, conduct on to D the force
whereby it is seized or conformed, yet not so
powerfully as C is seized by B. And these iron
nails derive the force from the mere contact,
and from the presence of the loadstone without
contact, and they retain it in their bodies, as
will be shown when we treat of Direction
(Book in). For the iron does not assume these
powers only while in presence of a loadstone,
nor does it hold them of the stone only momen-
tarily as Themistius supposes in his Physica, vin.
The best iron (steel) is solicited by the load-
stone from a greater distance, a greater weight
of it is lifted, it is more powerfully held, and it
acquires greater force, than does common,
cheaper iron, for it is made of the best ore or of
loadstone, and is imbued with superior forces;
but iron from impure ores is weaker, and is at-
tracted more feebly. As for what Fracastorio
writes, of having seen a bit of loadstone that
on one side attracted loadstone but not iron, on
another side attracted iron but not loadstone,
and on another attracted both — proof, accord-
ing to him, that in one spot there was more
loadstone, in another more iron, in the third
the two were present equally ; hence the differ-
ence in the attraction— all this is utterly er-
roneous, and the result of mal-observation on
the part of Fracas torio, who did not know how
to present one loadstone to another properly.
Loadstone attracts iron and loadstone if both
be properly situated, and free to move and un-
restrained. A light object is more readily moved
from its position and place than a heavy one,
for heavy objects make greater resistance, but
a light object bestirs itself to meet a heavy one
and is pulled by it.
CHAPTER 5. In what manner the energy inheres in
the loadstone
THAT the loadstone draws loadstone, iron, and
other magnetic bodies was shown in Book i, as
also by what forces the magnetic coition is reg-
ulated; we have now to inquire how this energy
is ordered in magnetic bodies. Here we must
bring in the analogy of a large loadstone. A
magnetic body unites forcibly with a loadstone
if the loadstone is powerful, feebly if it be de-
fective or if it has from any fault become im-
paired. Loadstone does not attract iron with
equal force at every point; in other words, the
magnetic body does not tend with the same
force to every point of the loadstone; for the
loadstone has points (/.*., true poles) at which
its rare energy is most conspicuous. And the
regions nearest the poles are the stronger, those
remotest are the weaker; yet in all the energy
is in some sense equal. In the figure of a terrella,
Ay 5, are the poles, CD is the equinoctial line;
the greatest attractive force is seen at A and B.
At Cand D there is no force that attracts to the
body the ends of magnetic objects, for the forces
tend toward each of the poles. But the directive
force at the equator is strong. C and D are at
equal distances from both poles; hence a piece
of iron on the line CZ), being pulled in con-
trary directions, does not cling steadily, but it
stays and adheres to the stone only when it falls
to either side of the line. At E the attractive
force is greater than at F, for E is nigher the
pole. And this is not for the reason that there
is more energy resident at the pole, but be-
cause all the parts, being united in the whole,
direct their forces to the pole.
By the confluence of the forces from the
plane of the equinoctial toward the pole the
energy increases poleward, and absolute vertic-
ity is seen at the pole so long as the loadstone
remains whole; but let it be divided or broken
up, and in the separate parts the verticity will
find other abiding-places. For with change of
A H
H
G B I
mass always goes change of verticity. Hence, if
the terrella be severed along the line AB so as
to make two stones, the poles in the severed
parts will not be AB, but FG and HI. And
though these two stones now are so interrelated
ON THE LOADSTONE
that F does not tend to H, nevertheless if, be-
fore division, A was the north pole, F likewise
is now north, as is H also. For the verticity is
not reversed, as Baptista Porta erroneously af-
firms (Porta [Natural Magic], vn. 4)1; for
though Fand H are not so related as mutually
to attract, yet the two turn to the same point
of the horizon. If the hemisphere HI be cut in
two quarter spheres, one pole will be at H and
the other at /. The integral mass of the stone,
as I have said, gives to the vertex or pole a con-
stant place; and any part of the stone, before it
was hewed out of the rock might have been the
pole or vertex: but of this we shall have more
to say under Direction. For the present, the
thing to be understood and to be borne stead-
ily in mind is, that the poles are dominant in
virtue of the force of the whole, for (the mag-
netic empire being divided in two by the equi-
curves starting from every point of the equator
that divides the sphere into two equal parts:
from every point of the superficies from the
equator to the north on one side, and from the
equator to the south on the other. Hence the
verticity is, in each hemisphere, from the equi-
noctial circle to the pole. This force resides in
the whole mass. From A the energy is transmit-
ted to By from AB to C, from ABC to D, and
from them to E, and likewise from G to //; and
so on as long as the whole mass is one body. But
if the piece AB be cut out, though it be near
the equator, nevertheless the effect will be as
great on the magnetic action as if CD or DE,
equal quantities, had been taken away. For no
part has any supereminent value in the whole;
whatever it be, that it is because of the parts
adjoining, whereby an absolute and perfect
whole is produced.
noctial line) all the forces of the hemisphere
tend north, and, conversely, all those of the
other hemisphere tend south, so long as the
parts are united, as appears from the following
demonstration. For the whole force tends sep-
arately to the two poles along an infinity of
1 "But the two points we speak of are the end of the
right line, running through the middle of the stone from
North to South; if any man break the stone, and break
this line, those ends of the division will presently be of
another property and vertue, and will be enemies one to
the other: which is great wonder: for these two points,
when they were joined together, had the same force of
turning to the pole, but, now being parted asunder, one
will turn to the North, the other to the South, keeping
the same posture and position they had in the mine where
they were bred: and the same happens in the least bits
that are seen in the greatest loadstone."
Let HEQ be a terrella, £ a pole, M the centre,
HMQ the plane of the equinoctial circle. From
every point of the equinoctial plane the energy
reaches out to the periphery, but differently
from each: for from A the formal energy goes
toward CFNE and to every point betwixt C
and E (the pole), and not toward B\ neither
from G toward C. The attractive force in the
region FGH is not strengthened by the force
residing in the region GMFE; but FGH in-
creases the energy in the rising curve FE. Thus
energy never proceeds from the lines parallel
to the axis to points above those parallels, but
always internally from the parallels to the pole.
From every point of the plane of the equator
the energy goes to the pole £; the point F de-
WILLIAM GILBERT
H
Diagram of the magnetic energy diffused from the plane
of the equator to the periphery of a terrella or of the earth
rives its forces only from GH, and the point N
from OH] but the pole E is strengthened by
the whole plane HO. Therefore this mighty
power has here its chief excellency; here is its
throne, so to speak. But in the intervals at F,
for example, there resides so much attractional
energy as can be given by the section HG of the
plane.
CHAPTER 6. How magnetized iron and smaller load-
stones conform to the terrella and to the earth itself,
and are governed thereby
COITION of bodies that are separate from one
another, and that cohere naturally, takes place
by another sort of movement, if they be free
to move. The terrella sends its force abroad in
all directions, according to its energy and its
quality. But whenever iron or other magnetic
body of suitable size happens within its sphere
of influence it is attracted; yet the nearer it is
to the loadstone the greater the force with
which it is borne toward it. Such bodies tend to
the loadstone not as toward a centre nor to-
wards its centre: that they do only at its poles,
*'.*., when that which is attracted and the pole
of the loadstone, as well as its centre, are in a
right line. But in the intervals between they
tend to it in an oblique line, as seen in the fig-
ure below, wherein is shown how the force goes
out to the magnetic associate bodies within the
sphere. At the poles the line is a right one. The
nearer the parts to the equinoctial circle the
ON THE LOADSTONE
43
more obliquely do magnetic bodies attract, but
the parts nearer the poles attract more directly;
at the poles themselves attraction is in a right
line. All loadstones alike, whether spherical or
oblong, have the self-same mode of turning to
the poles of the world; but it is easiest to exper-
iment with oblong ones. For whatever the shape,
verticity is present, and there are poles; but
owing to imperfect and irregular shape, load-
stones are often subject to drawbacks, and are
interfered with in their movements. If the load-
stone be oblong, with vertices at the extremi-
ties and not at the sides, it attracts best at the
vertex; for the parts convey to the poles a
greater force in right lines than in oblique. Thus
do the loadstone and the earth conform mag-
netic movements.
CHAPTER 7. Of the potency of the magnetic force,
and of its spherical extension
THE magnetic force is given out in all direc-
tions around the body; around the terrella it is
given out spherically; around loadstones of oth-
er shapes unevenly and less regularly. But the
sphere of influence does not persist, nor is the
force that is diffused through the air permanent
or essential; the loadstone simply excites mag-
netic bodies situated at convenient distance. And
as light— so opticians tell us— arrives instantly
in the same way, with far greater instantaneous-
ness, the magnetic energy is present within the
limits of its forces; and because its act is far
more subtile than light, and it does not accord
with non-magnetic bodies, it has no relations
with air, water, or other non-magnetic body;
neither does it act on magnetic bodies by means
of forces that rush upon them with any motion
whatever, but being present solicits bodies that
are in amicable relations to itself. And as a light
impinges on whatever confronts it, so does the
loadstone impinge upon a magnetic body and
excites it. And as light does not remain in the
atmosphere above the vapors and effluvia nor
is reflected back by those spaces, so the magnet-
ic ray is caught neither in air nor in water. The
forms of things are in an instant taken in by the
eye or by glasses; so does the magnetic force
seize magnetic bodies. In the absence of light
bodies and reflecting bodies, the forms of objects
are neither apprehended nor reflected; so, too,
in the absence of magnetic objects neither is the
magnetic force imbibed nor is it again given
back to the magnetic body. But herein does the
magnetic energy surpass light,— that it is not
hindered by any dense or opaque body, but
goes out freely and diffuses its force every
whither. In the case of the terrella and in a
spherical loadstone the magnetic energy extends
outside the body in a circle; yet in the case of
an oblong loadstone it does not extend out in a
circle, but into an area of form determined by
the shape of the stone, as in the stone A, in the
figure, the energy reaches to the limits FC/),
everywhere equidistant from the stone A.
C
CHAPTER 8. Of the geography of the earth and the
terrella
WE have next to speak of magnetic circles and
magnetic limits, so that what follows later may
be better understood. Astronomers, in order to
account for and observe the movements of the
planets and the revolution of the heavens, as
also more accurately to describe the heavenly
order of the fixed stars, have drawn in the
heavens certain circles and bounds, which geog-
raphers also imitate so as to map cut the diver-
sified superficies of the globe and to delineate
the fairness of the several regions. In a different
sense we accept those bounds and circles, for we
have discovered many such, both in the ter-
rella and in the earth; but these are determined
by nature itself, and are not merely imaginary
lines. Geographers make a division of the earth
chiefly by defining the equator and the poles;
and these bounds are set and defined by nature.
Meridians, too, indicate tracks from pole to
pole, passing through fixed points in the equator;
along such lines the magnetic force proceeds
and gives direction. But the tropics and the
arctic circles, as also the parallels of latitude,
are not natural bounds described on the earth;
yet all these parallel circles indicate that a cer-
tain conformity between themselves exists
among regions of the earth situate in the same
latitude or diametrically opposite to them. All
these are of service to mathematicians in con-
structing globes and maps. Thus such circles
are of use in the terrella, but they need not be
drawn as geographers draw them— on the sur-
face, for the loadstone may be perfectly even
and uniform all over. Nor are there any "upper"
44
WILLIAM GILBERT
or "lower" parts, in the terrestrial globe, as
there are also none in the terrella, save perhaps
that one may choose to call these parts "upper"
which are at the periphery and those "lower"
which are nigher the centre.
CHAPTER 9. Of the equinoctial circle of earth and
terrella
THE equinoctial circle imagined by astrono-
mers, which is equidistant from both poles and
divides the earth in the middle, measures the
movements of their primum mobile or tenth
sphere,1 and is called the zone of the primum
mobile-, it is called "equinoctial" because when
the sun is in this circle — which must happen
twice a year— the days are of equal length with
the nights. This circle is designated also xquidi-
ali$\ hence the Greeks give it the name tarjjuept-
v6s (which means the same, "equal day"). And
it is also well called "equator," for it divides the
whole globe of the earth from pole to pole in
two equal parts. To the terrella also is justly as-
signed an equator whereby its power is distrib-
uted between two parts. By the plane of this
equator, as it passes through the centre, the
whole terrella is divided into two parts equal
in mass and in verticity, and imbued with equal
energy, as though a wall stood betwixt the two
verticities.
CHAPTER 10. The earth's magnetic meridians
GEOGRAPHERS have devised meridians for the
purpose of distinguishing the longitude and lat-
itude of regions. But the magnetic meridians
are numberless, and, even as the earth's merid-
ians, they pass through fixed and opposite points
in the equator and through the poles. On them
also is magnetic latitude measured. By means
of them we understand declinations; and along
them there is a fixed direction toward the poles,
except when the magnetic body for any cause
varies, and is jostled out of the right course.
The meridian commonly called magnetic is not
properly magnetic, neither is it a meridian, but
is supposed to pass through the limits of varia-
tion in the horizon. Variation is in fact a faulty
deviation from the meridian. In various places
it is not fixed or constant in any meridian.
CHAPTER 11. Parallels
IN parallel circles the same energy and equal
potency is seen throughout, when different
magnetic bodies are placed on one and the same
parallel, either of the earth or of the terrella.
For the bodies are at equal distances from the
1 For primum mobile, see Book vi, 3.
poles and have equal changes of declination, and
are attracted and held and come together
under the action of like forces; just as regions
of the earth on the same parallel, though they
may differ in longitude, are said to have still
the same quantity of daylight and the same
climate.
CHAPTER 12. The magnetic horizon
AN horizon is a great circle separating the things
seen from those that are out of sight, as one
half of the heavens is always plainly visible while
another half is always hid. So it seems to us by
reason of the great distance of the starry sphere;
yet the difference is in the ratio of the earth's
semi-diameter to the semi-diameter of the star-
ry heavens— a difference not perceived by the
senses. But we take the magnetic horizon to be
a plane perfectly level throughout, tangent to
the earth or to the terrella at the place of the
region, with which plane the semi-diameter,
whether of the earth or of the terrella, being
extended, makes right angles on all sides. Such
a plane is to be imagined for the earth, and for
the terrella likewise, for the sake of magnetic
proofs and demonstrations. For we are consid-
ering the bodies themselves, and not the general
aspects of the world. Therefore, not with refer-
ence to sight — for that varies according to the
elevation of regions — we assume in magnetic
demonstrations a sensible horizon, not what is
called by astronomers the rational horizon.
CHAPTER 13. Of the magnetic axis and poles
A LINE drawn through the centre of the earth
(or of the terrella) to the poles is called the
axis. The poles are so called by the Greeks (TTO-
Xot, bird TOV wo\€lv — poloi from po/ein, to re-
volve), and by the Latins cardines (hinges, piv-
ots) and vertices (centres of a whirling motion) ;
and these names were given to signify that the
world rotates and is ever whirling. We propose
to show that the earth and the terrella are by
the magnetic force made to revolve round these
poles, whereof that one in the earth which points
to Cynosura2 is called the North, the Boreal, or
the Arctic pole; the opposite one is called the
South, Austral, or Antarctic pole. And neither
in earth nor in terrella do the poles exist merely
for the sake of rotation; they are furthermore
reference points of direction and of position —
on the one hand towards one's destination on
the earth, and on the other hand as regards their
angular distance.
* Cynosure— the constellation of the Lesser Bear (Ursa
Minor) containing the polar star.
ON THE LOADSTONE
45
CHAPTER 14. Why the coition is stronger at the
pole than in the pans between equator and pole; and
the relative power of coition in different parts of the
earth and the terrella
WE have already shown that the supreme at-
tractional power is at the pole, while the weaker
and more sluggish power is in the parts nigh the
equator. And as in the declination it is seen
that this ordering and rotating force increases
as we advance from the equator to the poles, so
too does the coition of magnetic bodies grow
stronger by the same degrees and in the same
proportion. For at points remote from the pole
the loadstone does not pull magnetic bodies in a
right line toward its centre, but they tend to it
obliquely, and obliquely are attracted. For as a
very small chord of a circle differs from the
diameter, by so much do differ the attractional
powers of different parts of the terrella. For
inasmuch as the attraction is a coition to a body,
and magnetic bodies come together owing to
their natural tendency to turn to each other,
in the diameter drawn from pole to pole a body
impinges on the loadstone in a right line; but
not so in other parts. Therefore the less it turns
toward the body, the less and the more weak
is the coition and the cohesion. Let ab be the
poles. An iron bar or the other magnetic body
c is attracted at e\ yet the end that is pulled
does not tend toward the centre of the load-
stone, but obliquely toward the pole, and a
chord drawn from that end obliquely in the
direction in which the body is attracted is a
short one; the strength of the coition therefore
is less, and so too the attracted object turns at
a less angle to the terrella. But as from a body
at/a longer chord proceeds, so the action there
is stronger. At g the chord is still longer. At a
(the pole) it is longest of all (for the diameter is
the longest line), and thither do all the parts
send their forces: there stands, as it were, the
citadel, the judgment-seat, of the whole region
— not that the pole holds this eminence in its
own right, but because it is the depository of
forces contributed to it by all the other parts;
it is like soldiers bringing reinforcement to their
commander. Hence a rather oblong loadstone
attracts better than a spherical one, if its length
stretch from pole to pole, and yet the two may
be from the same mine, and be of equal size and
volume. The way is longer from one pole to the
other in the oblong stone, and the forces sup-
plied by the other parts are not so scattered as
in a spherical loadstone and the terrella; they
are better massed and united, and thus united
they are stronger and greater. But a flat or ob-
long loadstone is much less effective when the
length is in the direction of the parallels, and
the pole ends neither in a point nor in a circle
or sphere, but lies flat on a plane surface so as
to be held for something abject and of no ac-
count, for its unfit and unadaptable form.
CHAPTER 15. The magnetic force imparted to iron
is more apparent m an iron rod than in an iron sphere
or cubey or iron of any other shape
IT has been already said that an oblong load-
stone lifts a greater weight of iron: so in a long
piece of iron rubbed with a loadstone the mag-
netic force is stronger if the poles are at the
ends; for the magnetic forces, which are sent to
both ends from the poles, are concentrated at
the narrow terminals, and not diffused. In
square and other angular figures the force is
scattered, nor does it proceed in right lines or
along suitable arcs. The iron sphere, too, though
it hath the figure of the earth, still has less at-
traction for magnetic bodies for the same rea-
son; hence an excited iron spherule acts with
less force on iron than does a magnetized bar of
the same weight.
CHAPTER 16. That motion is produced by the mag-
netic force through solid bodies interposed: of the
interposition of a plate of iron
AN iron wire passed through a suitable piece of
cork, or a needle poised on a point or in a mari-
ner's compass, is set in motion when a loadstone
is brought near it or is passed beneath it, though
the water, the vessel, or compass- box stand be-
tween. No hindrance is offered by thick boards,
or by walls of pottery or marble, or even of met-
als: there is naught so solid as to do away with
this force or to check it, save a plate of iron.
Whatever substances are interposed, however
dense they be, as they do not annul the force
nor obstruct its path, so do they in no wise
hinder or lessen or retard. Nor is the whole of
46
WILLIAM GILBERT
the force suppressed by a plate of iron, but in
part diverted. For when the force enters the
middle of an iron plate placed within the sphere
of magnetic influence or directly over the pole
of the loadstone, that force is distributed chiefly
to the extremities, so that the rim of a circular
plate of suitable size attracts pieces of iron wire
at all points. The same is seen in a long iron rod
rubbed with a loadstone in the middle; it has
the same verticity at both ends. In the figure,
CD is a long rod magnetized in the middle by
the north pole E\ C is a south end or south pole,
and D is another south end. But here note the
singular fact, that a needle magnetized by that
pole turns to that pole, though the round plate
stands between, the plate not hindering, but
the attraction being only weaker; for the force
is scattered to the extremities of the plate, and
departs from the straight track, but yet the
plate in its middle retains the same verticity
with the pole when it is nigh it and alongside
it: hence does the needle magnetized by the
same pole tend to the centre of the plate. If the
loadstone is a weak one, the needle hardly turns
if an iron plate be interposed; for, being diffused
out to the extremities of the plate, the load-
stone's energy is less able to pass through the
centre. But let the plate be magnetized in the
middle by the pole, and then let it be removed
beyond the loadstone's sphere of influence, and
you shall see the point of the same needle go in
the contrary direction and quit the centre of
the plate, which before it sought: for outside of
the sphere of influence the plate has the con-
trary verticity, but near the loadstone it has
the same; for near the loadstone the plate is as
it were part of the loadstone and has the same
pole.
Let A be an iron plate near a pole; B a needle
with point tending toward the centre of the
plate, which plate has been magnetized by the
pole Cof a loadstone. Now if the same plate be
placed outside the sphere of magnetic influ-
ence, the point of the needle will not turn to
its centre, but only the crotch (the other end)
of the same needle. But an iron sphere inter-
posed (if it be not too large) attracts the point
of the needle at the other side of the stone, for
the verticity of that side is the same as that of
the adjoining pole of the loadstone. And this
turning of the needle's point (i.e., the end of it
magnetized by contact with that pole) and of
rr\
its cross (other end) at a considerable distance
takes place with an iron sphere interposed,
whereas it would not take place at all were the
space between vacant; for the magnetic force
travels through bodies and is continued on by
them.
Let A be a terrella, B an iron sphere, F a
needle between the two bodies, with its point
magnetized by the pole C. In the second figure
A is the terrella, Ca pole, B an iron sphere: the
needle tends toward C, the terrella's pole,
through the iron sphere. The needle thus placed
between terrella and sphere vibrates more for-
cibly toward the pole of the terrella, because
the loadstone imparts instantaneous verticity
to the opposite sphere. The earth's efficiency is
the same, produced by the same cause. For if
in a thick box made of gold (the densest of met-
als) or glass, or marble, you put a needle free to
revolve, that needle, in spite of the box, will
show that its forces are most closely allied to
and unified with those of the earth; of its own
accord and instantly, regardless of the box that
prisons it, it turns to its desiderated points of
north and south. And it does the same though
it be shut up in iron vaults sufficiently roomy.
Whatever bodies are produced here on the earth
or are manufactured from nature's products by
art, all consist of the matter of the globe: such
bodies do not interfere with the prime poten-
cies of nature derived from the primary form;
nor can they withstand them, save by contrary
ON THE LOADSTONE
forms. But no forms of mixed bodies are inimi-
cal to the innate primary form, though some of
them oft do not accord among themselves. On
the other hand, in all the bodies that have a
material cause of attraction (e.g., amber, jet,
sulphur) action is hindered by interposition of
a body (as paper, leaves, glass, etc.), and the
way is obstructed and blocked so that that
which is exhaled cannot reach the light body
that is to be attracted. But coition and move-
ment of the earth and the loadstone, though
corporeal hindrances be interposed, are shown
also in the efficiencies of other chief bodies that
possess the primary form. The moon, more than
the rest of the heavenly bodies, is in accord
with the inner parts of the earth because of her
nearness and her likeness of form. The moon
causes the movement of the waters and the
tides of ocean; makes the seashore to be covered
and again exposed twice between the time she
passes a given point of the heavens and reaches
it again in the earth's daily rotation: this move-
ment of the waters is produced and the seas
rise and fall no less when the moon is below the
horizon and in the nethermost heavens, than
when she is high above the horizon. Thus the
whole mass of the earth, when the moon is be-
neath the earth, does not prevent the action of
the moon; and thus in certain positions of the
heavens, when the moon is beneath the horizon,
the seas nearest to our countries are moved, and,
being stirred by the lunar power (though not
struck by rays nor illumined by light), they rise,
approach with great impetus, and recede. Of
the reason of this we will treat elsewhere : suffice
it here just to have touched the threshold of the
question. Hence, here on earth, naught can be
held aloof from the magnetic control of the
earth and the loadstone, and all magnetic bod-
ies are brought into orderly array by the su-
preme terrene form, and loadstone and iron
sympathize with loadstone though solid bodies
stand between.
47
only 4 ounces of iron will now lift 12 ounces.
But the greatest force of the co-operating or
rather unified matter is seen when two load-
stones fitted with these projections are so joined
as mutually to attract and lift each other: thus
may a weight of 20 ounces be lifted, though
either stone unarmed would lift only 4 ounces.
Iron is held faster by an armed loadstone than
by one not armed, and hence it lifts greater
weights, because iron clings more strongly to
the armed stone: for, by the contiguous pres-
ence of the loadstone, the iron of the armature
and the iron attracted are bound fast together;
and when the armature has imbibed the mag-
netic energy by reason of the presence of the
loadstone, and another piece of iron adjoining
at the same time derives force from the presence
of a loadstone, the two unite energetically.
Hence when two powerful armatures are in con-
tact they cohere strongly. This is proved in
Book in. 4, by iron rods cohering, as also where
we mention the transformation of steel-filings
into a concreted mass. For this reason iron sit-
uate near a loadstone takes away from it pieces
of iron of suitable weight, provided only it be
in contact with them; else, however near they
may be, it does not match them. For masses of
magnetic iron do not, within the field of a load-
stone or near a loadstone, attract more strongly
than the loadstone attracts any iron; but once
they are in contact with each other they unite
more strongly, and become as it were clamped
together, though with the same forces at work
the substance remains the same.
CHAPTER IS. An armed loadstone does not endow
with greater force magnetized iron than does an un-
armed one
CHAPTER 17. Of the iron helmet (cap) of the load-
stone, wherewith it is armed at the pole to increase
its energy; efficiency of the same
A CONCAVE hemisphere of thin iron, a finger's
width in diameter, is applied to the convex po-
lar superficies of a loadstone and properly fast-
ened; or an iron acorn-shaped ball rising from
the base into an obtuse cone, hollowed out a
little and fitted to the surface of the stone, is
made fast to the pole. The iron must be the best
(steel), smooth, polished, and even. Fitted with
this contrivance, a loadstone that before lifted
TAKE two pieces of iron, one magnetized with
an armed and the other with an unarmed load-
stone, and apply to one of them a weight of iron
proportioned to its powers: the other loadstone
will lift the same weight, and no more. Two
needles also turn with the same velocity and
constancy toward the poles of the earth, though
one needle may have been touched by an armed
magnet and the other by one unarmed.
CHAPTER 19. That unition is stronger with an armed
loadstone; heavier weights are thus lifted; the coition
is not stronger, but commonly weaker
THAT an armed loadstone lifts a greater weight
is evident to all; but iron is drawn from the
same distance, or rather from a greater distance,
to the loadstone when the stone is without the
iron helmet. This is to be tried with two pieces
48
WILLIAM GILBERT
of iron of the same weight and form at equal
distance, or with one and the same needle, test-
ed first with the armed then with the unarmed
stone, at equal distances.
CHAPTER 20. That an armed mag-
net lifts another, and that one a
third: this holds good though there
be less energy in the first
ARMED loadstones duly joined to-
gether cohere firmly and form
one; and though the first be weak,
the second nevertheless clings to
it, not alone with the force of the
first, but of the second, the stones
thus helping each other: to the
second a third will often cling,
and with strong loadstones a
fourth to the third.
CHAPTER 21 . That when paper or other medium is
interposed, an armed loadstone does not lift more
than one unarmed
IT has been shown above that an armed load-
stone does not attract at a greater distance than
an unarmed one, but that it lifts a greater quan-
tity of iron, if it be in contact with the iron and
continuous therewith. But put a leaf of paper
between, and this intimate coherence is hind-
ered, nor are objects of iron held together by the
action of the loadstone.
CHAPTER 22. That an armed loadstone does not
attract iron more than an unarmed one; and that
the armed stone is more strongly united to the iron, is
shown by means of an armed loadstone and a cylin-
der of polished iron
ON a plane surface lay a cylinder too heavy for
the unarmed loadstone to lift; then, with paper
between, apply at the middle of the cylinder the
pole of an armed loadstone: if the cylinder is
pulled by the loadstone, it follows after it with
rolling motion; but when there is no paper be-
tween, the cylinder, joined to the loadstone, is
pulled by it, and does not roll at all. But if the
same loadstone be unarmed, it pulls the rolling
cylinder with the same velocity as does an armed
loadstone with paper between, or wrapped in
paper.
Armed loadstones of different weights, force,
and shape, but out of the same
mine, show an equal degree of
strength in adhering to or hanging
from iron objects of suitable size
and shape. The same is true of un-
armed ones. A suitable piece of iron
applied to the under side of a load-
stone that hangs from a magnetic
body heightens the energy of the
loadstone, so that it clings with
greater force. For a pendent load-
stone clings faster to the body
above, to which it is attached,
when a piece of iron is applied and
hangs from it, than when a piece of
lead or other nonmagnetic material
is fastened to it.
A loadstone, whether armed or
not, attached by its proper pole to
the pole of another loadstone,
armed or not, makes that other lift
a greater weight at its opposite end.
The same thing is seen when iron is
applied to the pole of a loadstone,
viz., the opposite pole carries a
greater weight of iron : thus, as in
the figure, the loadstone with a bar
of iron superposed carries the bar below, but
cannot carry it if the upper piece be removed.
Magnetic bodies in conjunction form one mag-
netic body; hence, the mass increasing, the
magnetic energy increases also.
An armed loadstone, as also an unarmed one,
leaps more quickly to a large mass of iron and
combines with it more strongly than with a
small mass.
CHAPTER 23. The magnetic force makes motion to-
ward union, and when united connects firmly
MAGNETIZED objects cohere well and duly to
one another according to their forces. Pieces of
iron in the presence of a loadstone, though not
in contact with it, come together, eagerly seek
and seize one another, and when in conjunc-
tion are, as it were, glued together. Iron dust or
iron reduced to a powder, packed in paper
tubes, and placed on the meridian of a load-
stone or merely brought near it, coalesces into
one mass, and in an instant the many particles
come together and combine; and the multi-
tude of united grains acts on a piece of iron and
attracts it, as though they formed but one con-
tinuous rod of iron, and take the north and
ON THE LOADSTONE
49
south direction when laid on the loadstone. But
if they be taken away from the stone to any
distance, the particles, resolved again to their
original condition, separate, and each stands
alone: thus it is that the foundations of the earth
are conjoined, connected, held together, mag-
netically. So let not Ptolemy of Alexandria,
and his followers and our philosophers, main-
tain that the earth will go to pieces, neither let
them be alarmed if the earth spins round in a
circle.
Iron-filings when made hot are attracted by
the loadstone not so strongly nor from as great
a distance as if they were not heated. A load-
stone subjected to any great heat loses some of
its energy; for its humor is dissipated, and so
its peculiar nature is marred. So, too, a mass of
iron-filings, if roasted in a reverberatory furnace
and changed to crocus M arris, is not attracted
by a loadstone; but if it has not been very high-
ly heated, not quite wasted, it clings to load-
stone, though more feebly than iron that has
not been put in fire. For crocus M arris has noth-
ing of the form of iron left; but metal that has
been made hot takes heat from the fire, and in
its vitiated substance the magnetic powers are
less powerfully awakened by the loadstone, and
iron that has quite lost its nature is not attract-
ed by the loadstone.
CHAPTER 24. That iron within the field of a load-
stone hangs suspended in air, if on account of an
obstacle it cannot come near
IRON within the magnetic field tends toward
the points of the stone that have the most ener-
gy, if it be not hindered by force or by the mat-
ter of an intervening body ; and this is so wheth-
er the iron tends downward to the loadstone, or
seeks it from one side and obliquely, or whether
it leaps up to it. But if on account of an obstacle
it cannot reach the stone, it sticks to the obsta-
cle and there remains, yet is held by a less con-
stant bond, for, owing to the greater intervals
and distances, the association (with the load-
stone) is less amicable. Fracastorio, in his Chap-
ter 8, Desympathia, says that a piece of iron will
be suspended in air so that it cannot move ei-
ther up or down if a loadstone be placed above it
that has an attractive force on the iron equal to
the force by which the iron tends downward:
thus the iron will stand fixed in mid-air. That
is ridiculous: for the nearer the loadstone the
greater always is its force; and hence the iron
that is lifted ever so little above the earth by
the loadstone's force must needs be steadily
drawn to it, and must cling to it. Baptista Porta
suspends in air a piece of iron (with a loadstone
fixed above), and holds back the iron by means
of a thin thread fastened to it beneath, so that
it shall not rise to the stone — hardly a very
brilliant idea. The piece of iron is pulled in a
perpendicular line by the loadstone, though the
two are not in contact, but only near each oth-
er; but, as on account of the greater nearness,
the iron mass is stirred by the force that was lift-
ing it, straightway it speeds to the loadstone and
clings to it. For the iron, the nearer it comes to
the loadstone, the more is excited, and the
stronger is the attraction.
CHAPTER 25. Intensifying the loadstone* s forces
ONE loadstone far surpasses another in energy,
for one will snatch up almost its own weight of
iron, while another is hardly able to move the
smallest particle. All animals and plants that pos-
sess life have need of victual of some sort, to the
end their powers may last and become firmer
and stronger. But iron is not attracted by the
loadstone, as Cardan and Alexander Aphrodise-
us supposed, so that it may be nourished with
morsels of it; neither does the loadstone gain
strength from iron-filings as from a nutritious
food. Baptista Porta, having his doubts about
this view, and wishing to make an experiment,
took a loadstone of determinate weight and
buried it in iron-filings of a weight not un-
known; and, after he had left it there many
months, he found the stone heavier, the filings
lighter. But the difference was so minute that
Porta was uncertain as to the truth. This ex-
periment of Porta's does not prove that the
stone devours anything, nor does it show any
process of nutrition, for minute quantities of
filings are easily lost by handling. So, too, a very
small quantity of the iron dust may adhere to
some small part of the loadstone and not be
noticed, thus adding somewhat to the weight
of the stone; but that is a superficial accretion,
and can be brushed off without much difficulty.
Many think that when weak and sluggish the
stone can bring itself back to a better condition,
and that a very strong stone can endow a weaker
one with the highest degree of force. Is it as
when animals gain strength when they feed and
are filled ? Is a remedy found for the loadstone
in addition or subtraction of something? Is
there aught that can restore this primary form
or give it anew? Surely nothing can do such a
thing save what possesses magnetic properties.
Magnetic bodies can restore soundness (when
not totally lost) to magnetic bodies, and can
give to some of them powers greater than they
WILLIAM GILBERT
had originally; but to those that are by their
nature in the highest degree perfect, it is not
possible to give further strength. Hence the
more infamous becomes all the charlatanry of
Paracelsus, who declares that the loadstone's
force and energy may be increased and trans-
formed to tenfold what it is naturally. And the
way of doing this is, so to speak, to half-candes-
cify the loadstone, i.e., to make it very hot, yet
so that it does not reach white heat, and then
immediately to dip it in oil of vitriol made from
the best Corynthian steel, letting it become sat-
urated. "In this way," says Paracelsus, "you
can give to a loadstone such strength that it will
pull a nail out of a wall, and perform many other
the like marvels impossible for a common load-
stone." But a loadstone so dipped not only ac-
quires no force, but suffers some loss it already
hath. A loadstone rubbed and smoothed with
steel is made better. When covered with filings
of the best iron or pure steel, not rusty, it retains
its properties. Sometimes, too, a good strong
loadstone gains some strength when rubbed on
its opposite pole with the pole of another load-
stone: it takes in force. In such experiments it
is well to observe the earth's pole, and to lay
down in the direction required by the mag-
netic laws the stone that one wishes to make
stronger: this point we will establish hereafter.
A strong, large loadstone increases the power of
another loadstone, as also the power of iron. If,
on the north pole of a loadstone, you place an-
other loadstone, the north pole of the second
becomes stronger, and a piece of iron clings like
an arrow to the north pole a, and not at all to
the south pole b. And the pole 0, when it is in
a right line above with the axis of both load-
stones, they being joined according to the mag-
netic laws, raises the piece of iron to the per-
pendicular: this it cannot do if the larger load-
stone be moved away, for its strength is insuffi-
cient. But as a ball of iron on the pole of the
tcrrella raises the piece of iron to the perpendic-
ular, so, at the side, the iron is not directed to-
ward the centre, but stands oblique and sticks
everywhere; for in the iron ball the pole is ever
the point of contact with the terrella's pole, and
it is not constant, as it is in the smaller terrella.
The parts of the earth, as of all magnetic bodies,
are in accord and enjoy neighborhood with
each other: there is in them all mutual love,
undying good-will. The weaker loadstones are
refreshed by the stronger ones, and the less vig-
orous bring no damage to the more vigorous.
Yet a strong loadstone exerts more attraction
in another strong one than in one that is feeble,
for a vigorous stone contributes forceful action,
and itself hastes, flies to the other, and solicits
it vehemently ; accordingly there is co-operation
and a clearer and stronger cohesion.
CHAPTER 26. Why the love of iron and loadstone
appears greater than that of loadstone and loadstone,
or iron and iron when nigh a loadstone and within
its field
ONE loadstone does not attract another on all
its sides as it does iron, but only at one fixed point :
hence the poles of the two must be properly ar-
ranged, else they do not duly and powerfully
cohere. But this arranging is not easy nor the
work of an instant: therefore one loadstone will
seem to be refractory toward another, whereas
they may be in perfect harmony. Iron, sud-
denly impressed by a loadstone, is not only at-
tracted by it, but is renovated and its powers
enhanced, whereby it pursues and solicits the
loadstone with a force not less than its own, and
also makes captive other iron objects. Suppose
a little iron bar firmly adhering to a loadstone:
if you bring near this piece of iron an iron rod,
but without touching the loadstone, you shall
see the iron instantly follow the rod, relinquish-
ing the loadstone, leaning toward the rod, and,
on contact, firmly adhering thereto; for iron in
union and contact pulls more vigorously
another piece of iron within the field of a
loadstone than does the loadstone itself.
The natural magnetic force, which in iron
lies confined and asleep, is awakened by a
loadstone, associates itself with it, and
comes into sympathy with it in virtue of
the primary form: hence comes the per-
fect magnetized iron, which is as strong
as the loadstone itself; for as the one im-
parts and arouses, so the other conceives,
and, being awakened, endures, and by its
very act gives back the force again. But
in so much as iron is liker to iron than is
ON THE LOADSTONE
loadstone, and in two pieces of iron within the
field of a loadstone, the nighness of the latter
enhances the powers of both: then, their forces
being equal, likeness of substance becomes de-
cisive, and iron gives itself up to iron, and the
two pieces are united by their most like (iden-
tical) and homogeneous forces. This is effected
not only by coition, but by a firmer union; and
a steel cap or snout (glansvelnasus) properly ad-
justed to the pole of a loadstone lifts greater
weights than can the stone by itself. When steel
or iron is made from loadstone or from iron ore,
the slag and impurities are separated from the
substance by a better fusion: hence usually such
iron contains the matter of the earth purged of
foreign admixture and dross, and more homo-
genie and perfect (than before smelting), albeit
deformed by fusion. And this matter, when
acted on by a loadstone, conceives the magnet-
ic virtue, and within the magnetic field is en-
dowed with force surpassing that of an inferior
loadstone, which is seldom without some ad-
mixture of impurities.
CHAPTER 27. That the centre of the magnetic forces
in the earth is the centre of the earth; and m the terrel-
la the terrella' s centre
THE rays of magnetic force are dispersed in a
circle in all directions; and the centre of this
sphere is not in the pole (as Baptista Porta
deems, Chap. 22), but in the centre of the
stone and of the terrella. So, too, the earth's '
centre is the centre of the earth's magnetic
movements, though magnetic bodies are not
borne direct toward the centre in the magnetic
movement save when they are attracted by the
pole. For as the formal power of loadstone and
earth promotes simply unity and conformity
between things separate, it follows that every-
where at equal distance from the centre or from
the convex circumference, just as at one point
it seems to attract in a right line, so at another
it can control and rotate the needle, provided
only the loadstone be not of unequal power.
For if at the distance G from pole D the stone
is able to attract the needle, then at an equal
distance A above its equator it can control and
rotate the needle. Thus the centre and middle
of the terrella is the centre of force, and thence
to the circumference of its sphere of influence
its magnetic virtues extend (for) equal distances
in all directions.
CHAPTER 28. That a loadstone does not attract to a
fixed point or pole only, but to every part of a terrella,
except the equinoctial circle
COITION is always strongest when pole touches
pole, for at the poles the force is greatest by
concert of the whole: hence one pole seizes the
other with greatest force. Points at distances
from the poles possess attractional power also,
but somewhat weaker and sluggish in the ratio
of the distance, so that finally in the equinoc-
tial line they are utterly enervate and faint.
The poles, too, do not attract as mathematical
points, nor does magnetized iron unite at its
poles only with the poles of a loadstone. On the
contrary, the coition takes place all over the
periphery, north and south, the force emanat-
ing from the whole mass. Magnetic bodies, how-
ever, are attracted feebly in the parts near the
equator, but quickly in the parts near the poles.
Wherefore not the poles alone, and not the parts
alone that are near the poles, attract and solicit
magnetic bodies; but magnetic bodies are con-
trolled and rotated and unite with other mag-
netic bodies according as parts neighboring and
adjoining lend their forces, which forces are
ever of the same potency in the same parallel,
except when otherwise distributed by causes
producing variation.
CHAPTER 29. Of difference of forces dependent on
quantity or mass
LOADSTONES coming from the same mine, and
not intermingled with neighboring metals or
ores, have the same potency; yet the stone that
is largest exhibits greatest force, as it carries the
greatest weight and has a wider sphere of influ-
ence. A loadstone weighing an ounce does not
lift an iron spike as does one that weighs a
pound, nor does its control reach so far, nor does
its force extend to such a distance. And if you
take from a one-pound stone a part, somewhat
of its power will be seen to leave also; for when
a part is taken away some of the energy is lost.
But when such part is duly applied and united
to the stone, though it be not cemented there
nor perfectly fitted in by the mere apposition,
WILLIAM GILBERT
the original strength is recovered, and the force
returns. Sometimes, however, the energy is in-
creased by detachment of a part because of mal-
formation of the stone, as when the force is
diffused through awkward corners.
In stones of different sorts the ratio of power
is different: one weighing a drachm may have
more force than another one of 20 pounds.
Many a loadstone is so weak that the force can
scarcely be noticed, and such faint magnets are
often surpassed by masses prepared of potter's
earth. But we may ask: supposing that a stone
of a given kind and of definite goodness, and
weighing a drachm, carries one drachm, whether
one weighing an ounce will carry an ounce, a
pound a pound, and so on? So it is, for in pro-
portion to size such loadstone has greater or
less strength: so that a loadstone of proportion-
ate size and weight, a drachm weight of which
lifts a drachm weight of iron, will, when
brought near a suitable great obelisk or enor-
mous pyramid of iron, attract it and pull it to it-
self, and that with no greater effort of its nature
and with no greater pains than when a drachm
weight of loadstone seizes a drachm weight of
iron. But in all such experiments the power of
the loadstones should be equal, the form of the
stones should be exactly proportioned: this is
true not less of an armed than of a naked load-
stone. As an experiment, take a loadstone
weighing 8 oz., which when armed lifts 12 oz.
of iron; cut off of this stone a part which, when
brought to the form of the whole stone as it
was before, shall weigh only 2 oz. : such a stone,
armed, lifts 3 oz. of iron. In this experiment it
is requisite that the form of the 3-oz. piece of
iron be the same as that of the i2-oz. piece; if
the 12 oz. mass rose in form of a cone, the 3-oz.
piece must assume a pyramidal form propor-
tioned to the figure of the original mass.
CHAPTER 30. The shape and the mass of an iron
object are important in magnetic coitions
IT was shown before that the shape and mass of
a loadstone are weighty factors in magnetic coi-
tions: similarly, the shape and mass of the iron
determine whether its force shall be great or
little. Oblong, bacilliform pieces are both more
quickly attracted and cling more firmly than
spherical or square pieces, and this for the causes
we have shown with regard to the loadstone.
It is also worthy of note, that when a smaller
iron object has attached to it a weight of dif-
ferent material, so that the weight of the two
shall equal that of another larger piece whose
weight is proportioned to the power of the
loadstone, it is not lifted by the loadstone like
the larger object; for the smaller piece is not so
powerfully attracted by the loadstone, because
it gives back less force, and only magnetic mat-
ter conceives the magnetic energy: foreign mat-
ter appended to such a body cannot take in mag-
netic force.
CHAPTER 31. Of oblong and round stones
IRON bodies are more forcibly attracted by an
oblong stone than by a round one, provided
only the pole of the stone is at the extreme end
of its length. The reason is that in the oblong
stone the magnetic body at the extremity is
directed straight toward a body wherein the
force proceeds in right lines and through a
longer diameter. But the oblong stone has only
little force on the side; for, plainly, the attrac-
tion at a and B is stronger in a round loadstone
at equal distance from the pole, than in randD.
CHAPTER 32. Some problems and magnetic experi-
ments on the coition, and repulsion, and regular
movement, of magnetic bodies
LOADSTONES that are equal come together with
equal mutual incitation.
Magnetized iron bodies that are in all re-
spects equal do also come together with equal
mutual incitation.
Iron bodies not magnetized, if they are equal,
and not hindered by their bulk, do also come
together with equal movement.
Two loadstones placed on suitable floats apart
on the surface of water, if they be suitably ar-
ranged within their magnetic field, attract each
other. So, too, a proportionate piece of iron on
one float hastes to a loadstone with the same
speed with which the magnet itself, afloat,
strives to reach the iron. For the two are im-
pelled from their own places on either side to
come together midway and coalesce. Two mag-
netized iron wires, floated in water by suitable
corks move forward to contact, and, with the
proper end on, strike and are joined.
With magnetic bodies that are equal, coition
is more vigorous, and quicker than repulsion
and separation. That magnetic bodies are more
sluggish in repelling than in attracting, is seen
ON THE LOADSTONE
53
in every magnetic experiment, as when load-
stones are borne on suitable floats on water, or
when magnetized iron wire or little bars are
driven through cork and set afloat in water, as
also in experiments with a needle. The reason
is that, since the power of coition is one thing,
the power of conformation and of ordering in
place is another, therefore repulsion and aver-
sation are the act of the force ordering in place;
but the coming together is the result of mutual
attraction to contact as well as of the force that
orders in place; />., it is due to a twofold force.
The ordering force is often only the forerun-
ner of coition, so that the bodies shall stand in
due position before the onset: hence they turn
in the direction of the points of coition, if they
be hindered from attaining those points. If a
loadstone be cut in two equal parts along the
meridian, the separated parts repel each other,
if the poles be placed at a suitable even distance
from each other; for they mutually repel with
greater velocity than is the case when pole is
wrongly opposed to pole. Thus the half B of a
loadstone, placed near the other half A^ repels A
on its float, because D withdraws from F and E
from C. But if B be again joined exactly with
/4, they come together and form one magnetic
body; yet when they are only near each other
they are mutually hostile. And if one half be
turned about so as to bring C opposite to D and
F to E, then A follows B within the field and be-
comes joined to it.
South parts of a stone retreat from south
parts, and north parts from north. Neverthe-
less, if you bring the south end of a piece of iron
near to the south part of the stone, the iron is
seized and the two are held ir friendly embrace;
as the verticity fixed in the iron is reversed and
changed by the presence of the more powerful
loadstone, which is more constant in its forces
than the iron. For they come together in ac-
cordance with nature, if either by reversal or
change there be produced true conformity and
orderly coition as well as regular direction.
Loadstones of identical shape, size, and strength
attract each other with equal force, and when
in wrong position repel with like energy.
Little rods of unmagnetized iron, though like
and equal, yet act on one another often with
different force; for as there are different grounds
for the acquisition of verticity and also of
strength and vigor, so the particles that are
most strongly excited by the loadstones them-
selves in turn act with most force.
Pieces of iron that have been magnetized at
one same pole of a loadstone repel one another
at the magnetized ends; and their other extrem-
ities are also mutually hostile.
In rotating needles when the points are mag-
netized but not the crotches, the latter repel
one another, but only feebly and in proportion
to length.
In like rotating needles when the points are
magnetized by the same pole of a loadstone the
crotches attract with equal force.
In a long rotating needle the crotch is attract-
ed feebly by the point of a short needle; the
crotch of a short one is attracted strongly by the
point of a long one, because the crotch of a long
needle has feeble verticity, but the point of a
long needle has strong verticity.
The point of a long needle repels the point
of a short one more strongly than the point of a
short needle repels that of a long one, if one of
them be poised free on a sharp point and the
other held in the hand; for though both have
been equally magnetized by the same loadstone,
still the longer one, by reason of its greater mass,
has greater force at its point.
In unmagnetized iron rods the south end of
one attracts the north end of another, and the
north end the south; the meridional parts, too,
repel meridional parts, and north parts north
parts.
If magnetic bodies be divided or in any way
broken up, each several part hath a north end
and a south end.
A needle is stirred by a loadstone at as great a
distance with an obstacle interposed as in air
and in an open medium.
Rods magnetized by friction with the pole of
a loadstone draw toward that pole and follow it.
Baptista Porta is therefore in error when he
says (Chapter 4) that "if you bring a part nigh
the part that gave it the force, it shudders, and
repels and drives it away, and attracts the con-
verse and opposite part."
The laws of rotation and attraction are the
same as between loadstone and loadstone, load-
stone and iron, and iron and iron.
54
WILLIAM GILBERT
When the parts of a magnetic body that has
been broken up by force and cut into pieces
are put together again and properly joined,
they form one body and their joint force is one;
nor have they separate poles.
The separated parts, if division has not been
made on the parallels, assume new poles, north
and south; if the division is along a parallel,
they may retain one pole in the same place as
before.
Iron rubbed and excited by a loadstone is
seized at the fitting ends by a loadstone more
powerfully than iron not magnetized.
If a small iron bar be set erect on the pole of a
loadstone, another bar-iron pin in touch with
its upper end becomes firmly attached thereto,
and if it be moved away pulls the standing bar
from the terrella.
If, to the nether end of the erect bar you ap-
ply the end of another bar, it does not cohere,
nor do they unite.
As a rod of iron pulls iron away from the
terrella, so does a small loadstone or a smaller
terrella albeit of less force. Here the iron bar C
coalesces with the terrella A, and thus its force
is enhanced and awakened magnetically both in
the end in conjunction and also in the distal
end by reason of its contact with the terrella;
the distal end furthermore receives energy
from the loadstone #, and the pole D of this
magnet also gains force by reason of its favour-
able position and the nearness of the pole E of
the terrella. Hence many causes co-operate to
make the bar C, attached to the loadstone B,
cling more strongly to that than to the terrella
A. The energy called forth in the bar, also the
energy called forth in the loadstone B, and Fs
native energy, all concur; therefore D is mag-
netically bound more strongly to C than E to C.
But if you turn the pole F to the iron C, then
C does not cling to F as it did before to D\ for,
within the magnetic field, stones so arranged
stand in an unnatural order: hence F does not
get force from E.
Two loadstones, or two magnetized pieces of
iron, duly cohering, fly apart on the coming of
a stronger loadstone or a stronger magnetized
mass of iron; for the newcomer, presenting the
opposite pole, puts one to flight and overmas-
ters it, and the mutual action of the two that
before were conjoined ceases. So the forces of
one of the bodies arc reduced and fail; and were
it possible, it would shake off its fellow, and,
turning about, would go rolling over to the
stronger. For this reason it is that magnetic
bodies held pendent in air drop to the ground
when the opposite pole of a loadstone is present-
ed to them; and this not because there is any
weakening or numbing of the forces of both of
the bodies before conjoined, as Baptista Porta
maintains, for pole cannot be hostile to both of
the ends that cohere, but to one only: this end
the newcomer, the stronger loadstone, drives
away from itself by presenting its opposite pole,
and thus one of the smaller bodies is compelled
to give up its friendly association with the
other.
CHAPTER 33. Of the difference in the ratio of strength
and movement of coition within the sphere of influ-
ence
IF the greatest weight that is attracted to a
loadstone at the nearest distance be divided into
a given number of parts, and the radius of the
sphere of magnetic attraction into the same
number of parts, the parts of the weight will
correspond to the intermediate parts of the
radius.
The sphere of influence extends farther than
the sphere of movement of any magnetic body,
for a magnetic body is affected at the outer-
most edge though it may not move with local
motion: that is done when the loadstone is
brought nearer. A needle, even a very small one,
turns round while remote from a loadstone,
though, at the same distance and free to move
and in no wise hindered, it does not come to the
loadstone.
ON THE LOADSTONE
55
The velocity of the movement of a magnetic
body to a loadstone is in proportion to the
strength of the loadstone, or its mass, or its
shape, or the nature of the medium, or the dis-
tance within the magnetic sphere of action.
A magnetic body approaches with greater
velocity a powerful loadstone than a sluggish
one, in the ratio of the respective energies of
the two loadstones. A smaller mass of iron, as
also one rather oblong in shape, is attracted
with the greater velocity. The velocity of the
movement of a magnetic body to a loadstone
varies according to the medium, for bodies
move with greater velocity in air than in water,
and in a serene atmosphere than in thick and
foggy weather.
In the ratio of distance, movement is quicker
from anear than from afar. At the outermost edge
of a terrella's field magnetic bodies move faint-
ly and slowly. In the immediate neighborhood
of the terrella the motor impetus is greatest.
A loadstone that in the outermost verge
of its field offeree, at the distance of one
foot, can hardly stir a rotating needle,
will, when connected with a long iron rod,
strongly attract and repel (accordingly as
its different poles are presented) the
needle at the distance of three feet, and
this whether the loadstone is armed or
unarmed. The iron rod should be of fit-
ting quality, and of the thickness of the
little finger.
For the energy of the loadstone awak-
ens verticity in the iron and passes in and
through iron to a far greater distance
than it extends through air.
The force also passes through a number of
pieces of iron conjoined at their extremities,
yet not so surely as through one continuous rod.
Steel-filings strewed on paper rise on end and
present the appearance of stubby steel hairs
when a loadstone is brought near above them;
when the loadstone is applied beneath, the hair-
like crop rises also.
Steel-filings, when the pole of a loadstone is
brought near, coalesce into one body; but when
it would come to the loadstone, the body is
broken up and rises to the steel in smaller masses
that still hold together.
But if the loadstone be beneath the paper,
the consolidated mass breaks up as before, and
into very many parts, each of which consists of
a multitude of grains; and they remain united,
like separate bodies; and while the lowermost
parts of these eagerly follow the pole of the load-
stone beneath, so the separate masses stand like
solid magnetic bodies. In like manner a bit of
iron wire one barley-corn or two in length
stands on end when a loadstone is applied either
beneath or above.
CHAPTER 34. Why a loadstone is of different power
in its poles as well in the north as in the south regions
THE extraordinary magnetic energy of the earth
is beautifully shown in the following neat ex-
periment: Take a terrella of no ordinary power,
or an oblong loadstone with equal cones form-
ing its polar ends; but in any figure not exactly
spherical it is easy to fall into mistakes, and the
experiment is difficult. In northern latitudes
raise the true north pole above the horizon
straight toward the zenith. Plainly it holds erect
on its north pole a larger bar of iron than could
the south pole of the same terrella if turned in
like manner toward the centre of the sky. The
same demonstration is made with a small ter-
rella set atop of a large one.
Let ab be the earth or a large terrella, and
ab a small terrella; a larger bar is raised erect
by the north pole of the small terrella than the
b pole of the same, if turned skyward, can raise
to the erect position. And the a pole of the
small terrella derives force from the greater,
turning from zenith to the plane of the horizon
or to the level. Now if, the smaller terrella hav-
ing its poles directed as before, you apply a
piece of iron to its lower or south pole, that will
attract and hold a greater weight than can the
south pole if that be turned down. Which is
thus shown: Let A be the earth or a terrella;
E the north pole or some point in high latitude;
let B be a large terrella above the earth, or a
small terrella above a larger one; D the south
pole: it is plain that D (south pole) attracts a
larger piece of iron, C, than can E (the north
pole), if that pole be turned downward to the
position Dj looking toward the earth or the ter-
WILLIAM GILBERT
rella in their northern regions. Magnetic bodies
gain force from other magnetic bodies if they
be arranged duly and according to their nature
in neighbourhood and within the sphere of in-
fluence; and hence, when a terrella is imposed
on the earth or on another terrella in such way
that the south pole looks toward the north pole
and north is turned away from north, the ener-
gy and forces of its poles are augmented. Hence
the north pole of a terrella in such position lifts
a heavier piece of iron than the south pole does
if that be turned away. In like manner the
south pole, gaining force from the earth or the
larger terrella when it is duly placed as nature
requires, attracts and holds heavier bars of iron.
In the other portion of the terrestrial globe, to-
ward the south, as also in the southern parts of
the terrella, the case is reversed, for, there, the
south pole of the terrella is strongest when distal,
as is the north pole of the terrella when it faces
the earth or terrella. The farther a place is from
the equinoctial line, whether of the earth or of
a terrella, the greater is seen to be the accession
offeree; but nigh the equator the difference is
slight; at the equator it is null; at the poles it is
greatest.
CHAPTER 35. Of a perpetual-motion engine actuated
by the attraction of a loadstone, mentioned by authors
CARDAN writes that out of iron and loadstone
may be constructed a perpetual-motion engine
— not that he saw such a machine ever; he mere-
ly offers the idea as an opinion, and quotes from
the report of Antonius de Fantis, of Treviso;
such a machine he describes in Book ix, De
rerum varietate. But the contrivers of such ma-
chines have but little practice in magnetic ex-
periments. For no magnetic attraction can be
greater (whatever art, whatever form of instru-
ment you employ) than the force of retention;
and objects that are conjoined, and that are
near, are held with greater force than objects
solicited and set in motion are made to move;
and as we have already shown, this motion is a
coition of both, not an attraction of one. Such
an engine Petrus Peregrinus, centuries ago, ei-
ther devised or delineated after he had got the
idea from others; and Joannes Taysner pub-
lished this, illustrating it with wretched figures,
and copying word for word the theory of it.
May the gods damn all such sham, pilfered,
distorted works, which do but muddle the
minds of students!
CHAPTER 36. How a strong loadstone may be
recognized
A STRONG loadstone sometimes lifts in air a
mass of iron weighing as much as itself; a weak
loadstone hardly attracts a bit of fine wire.
Those, then, are the stronger loadstones which
attract and hold the larger bodies, unless there
is some defect of shape, or unless the pole of the
stone is not properly applied. Besides, the
stronger loadstone, when afloat, more readily
turns its poles toward the poles of the earth or
the points of variation on the horizon. But the
stone that acts sluggishly, betrays some flaw in
itself, shows that its force is exhausted. Load-
stones are to be all prepared in the same way,
shaped alike, and made of the same size; for
when they are unlike and unequal, experiments
are doubtful. All loadstones are tested for
strength in the same way, viz., with a versorium
(rotating needle) held at some distance; the
stone that at the greatest distance is able to
make the needle go round is the best and strong-
est. Baptista Porta also rightly determines the
power of a loadstone by thus weighing in a bal-
ance. A piece of loadstone is put in one scale and
an equal weight of another substance in the oth-
er, so that the scales are balanced. Then some
iron lying on a board is brought nigh, so that
it shall cleave to the loadstone in the scale, and
the two bodies cohere perfectly at their points
of attraction; into the opposite scale sand is
poured gradually till the scale in which is the
loadstone separates from the iron. By weighing
the sand the force of the loadstone is ascer-
ON THE LOADSTONE
57
tained. So, too, we can make experiment and
find the stronger stone by weighing sand, if we
put in a pair of scales loadstones that balance
each other. Such is an experiment given by Car-
dinal Cusanus in his Statica, and from him Por-
ta would seem to have learned the one he cites.
The stronger loadstones turn readily toward the
poles or the points of variation; so, too, they
propel their floats and cause them and other
cumbrances, as so much wood, to wheel about.
In an inclination or dip instrument the greater
power of a loadstone is manifested and there
greater power is requisite. Hence loadstones are
stronger the more speedily they do their work,
and the more rapidly they travel from side to
side and return, and the sooner they come to a
standstill. Feeble, exhausted loadstones travel
more sluggishly, come to a rest more slowly,
stick at the pole less decisively, and are easily
displaced therefrom.
CHAPTER 37. Uses of the loadstone as it affects iron
BY means of magnetic coition we test an iron
ore. The ore is roasted in a furnace, is crushed,
washed, dried, and so is freed from foreign hu-
mours. The loadstone being thrust among the
particles collected from the bath attracts the
iron dust, which being removed by a feather
brush is caught in a crucible; again and again
the loadstone is dipped in and the iron dust
brushed into the crucible, till nothing remains
that it will attract. Then the powdered iron is
heated together with halinitro till it is melted
and becomes a mass of iron. Now if the load-
stone picks up the iron dust readily and easily,
we deem the ore to be rich; if slowly, the ore is
poor; if the loadstone seems quite to reject it,
the ore is judged to have little or no iron. By
the same method, iron particles may be sepa-
rated from particles of any other metal. And
many tricks are played by secretly attracting
bits of iron to light bodies, or causing a con-
cealed loadstone to attract the iron; to persons
who know not the cause, the movements of the
objects seem amazing. Any ingenious workman
may exhibit a great number of such tricks for
sport, with the air of one dealing in incantations
and magic.
CHAPTER 38. Of the attractions of other bodies
PHILOSOPHIZERS of the vulgar sort and mere
copyists oft repeat, from others* memoirs on
natural philosophy, opinions and errors with re-
gard to the attractional force of various bodies.
They will say, for example, that diamond at-
tracts iron and pulls it away from loadstone;
that loadstones differ, some attracting gold, oth-
ers silver, copper, lead — yea, flesh, water, fish.
The flame of sulphur is said to seek iron and
stones; so is white naphtha said to draw to it;
self fire. I have already said that inanimate nat-
ural bodies in no other wise attract or are at-
tracted on this terrestrial globe, save either
magnetically or electrically. It is therefore not
true that there are loadstones that attract gold
or other metals; for a magnetic body attracts
only a magnetic body. Fracastorio tells of having
seen a loadstone attracting silver. If that were
true, then it must necessarily have been be-
cause some iron had been artificially mixed
with the silver and lay hidden therein, or be-
cause nature had mixed iron with the silver (as
she does sometimes, though very seldom); for
iron is now and then mixed with silver by na-
ture, but silver with iron very rarely or never.
By false coiners and by avaricious princes, when
money is coined, iron is mixed with silver; an
instance of this we have in Anthony's denarius,
if what Pliny declares be true. So Cardan (led
into error, perhaps, by others) says there is a
certain kind of loadstone which attracts silver;
and he adds a very silly test of the thing: "If,"
says he, "a thin rod of silver be touched with
this and then poised in equilibrium, when it
comes to a standstill after being whirled, it will
point to silver (especially a large quantity),
though the same be buried in the ground; by
this means anybody may easily unearth hidden
treasures." He adds that "the stone must be of
the best," and that he never saw such stone.
Nor will he or anybody else ever see such a
stone or such an experiment. Cardan cites an
attraction, improperly so called, of flesh, which
is altogether unlike magnetic attraction; his
magnes creagus (or flesh-attracting loadstone, so
named because it clings to the lips) must be
cast out of the company of loadstones and of
the whole family of attractional bodies. Lemni-
an earth, red ochre, and sundry minerals have
this action, but it were absurd to say that they
attract. Cardan imagines another loadstone, a
third species as it were; if a needle be driven in-
to this, it may be thrust into a person's body
afterward without being felt. But what has at-
traction to do with numbing of sense, or what
is there in common between stupefaction and
the mind of a philosopher while he discourses
of attraction? Many are the stones, both of
natural origin and artificially compounded, that
possess the power of dulling the senses. The
flame of sulphur is by some said to attract be-
cause that it consumes certain metals by reason
WILLIAM GILBERT
of its penetrating force. So does naphtha at-
tract flame because it emits and exhales inflam-
mable vapor, and hence is set aflame at some
distance; even as the smudge of a candle that
has just been extinguished catches fire again
from another flame; for fire creeps to fire
through an inflammable medium. Of the suck-
ing-fish or remora, and how it stays ships, phi-
losophers have discoursed variously. It is their
custom oft to account with their reasonings for
this and many other fables, before ascertaining
that the thing is so in fact. Wherefore, approv-
ing and indorsing the absurdities of the ancients
they published the most blunderous theories
and ridiculous theses — e.g., that there are rocks
having the power of attraction and that there
the remora dwells; and they postulate of the
necessity of I know not what vacuum or how
produced. Pliny and Julius Solinus tell of the
stone cathochites and affirm that it attracts flesh
and holds one's hand, as loadstone holds iron
and amber holds chaff. But that is due solely to
its viscosity and its natural glutinousness, for it
adheres most readily to a warm hand. The sag-
da, or sagdo, is a gem of leek-green color men-
tioned by Pliny, Solinus, Albertus Magnus', and
Euace, who themselves make up or from others
copy the story that this stone has the peculiar-
ity of attracting wood. And there are others who
utter the nonsense that the wood attracted
cannot be pulled off, but has to be cutaway;
while some tell of a stone of this kind that clings
as firmly to ships' bottoms as do the barnacles
gathered on a long voyage. But though a stone
may cling to a surface, it does not therefore at-
tract; and if it did attract, surely it would draw
to itself chips and shavings electrically. A stone
of this sort was seen by Encelius in the hands
of a certain seaman; a weak stone, it was, hardly
able to attract the smallest twigs; and its color
was not a true leek-green. Diamond, carbuncle,
rock-crystal, and other stones attract in that
way. I say nothing of other fabulous stones, of
pantarbes whereof Philostratus affirms that it
attracts to itself other stones; of amphitane, said
to attract also gold. Pliny, in telling of the dis-
covery of glass, makes the loadstone attract
glass as it does iron; for when in speaking of the
mode of making glass he describes its nature, he
adds this concerning the loadstone: "In time the
skill of the workmen, clear sighted and resource-
ful, was no longer content with mixing in na-
tron; loadstone began to be added because it is
believed to attract to itself the liquid glass even
as it attracts iron." Georgius Agricola asserts
that "A portion of loadstone is added to the in-
gredients of glass (sand and natron), because it
is believed in our day as in early times that that
force (the magnetic) attracts to itself the mol-
ten glass even as it attracts iron, that it purifies
it when attracted, and changes it from green
or orange-yellow to clear white; but afterward
the fire consumes the loadstone," True it is in-
deed that loadstone of some kind (as the mag-
nesia employed by glass-makers, which has no
magnetic powers) is sometimes introduced into
and mingled with the material of glass, yet
not because that it attracts glass. But a red-
hot loadstone does not attract iron at all, nor
is iron at white heat attracted by loadstone;
and the loadstone is even destroyed by very
strong heat and loses its power of attraction.
Nor is this work of purifying the function
of loadstone alone in the glass furnace, but
also of certain pyrites and of readily combus-
tible iron ores; and these alone are used by
such of our glass-makers as make clear, fine
glass. These materials are mixed with sand,
ashes, and natron (just as other materials are
mixed with metals when they are smelted), so
that, when the contents of the furnace become
fluid glass, the well-known green and yellow
color may be purged away by the penetrant
heat. For no other matter reaches such degree
of heat or endures fire for the requisite length
of time that the material of the glass may be-
come perfectly fluid, and just then is burnt up
by the strong fire. But sometimes it happens
that on account of the magnetic stone, or mag-
nesia, or iron ore, or pyrites, the glass hath a
dusky tinge, these substances being too resist-
ant to fire and hence not being burnt up, or
having been introduced in too great quantity.
For this reason, glass-makers procure the right
sort of stone and carefully attend to the pro-
portion of ingredients in the mixture. Thus,
then, Georgius Agricola and later writers are
badly led astray by Pliny's stupid philosophy
when they declare that loadstone is needed by
glass-makers for its magnetic virtues and attrac-
tive force. And Scaliger (De subtil, ad Carda-
num) strays far from truth when, in treating of
magnetic bodies, he speaks of diamond attract-
ing iron; unless he means only that diamond
electrically attracts iron as it does bits of wood,
straws, and other small bodies of all kinds. Fal-
lopius thinks that quicksilver attracts metals in
virtue of an occult property, just as the load-
stone does iron, or as amber attracts chaff. But
there is no attraction properly so called when
quicksilver enters into metals. For metals im-
bibe quicksilver as clay does water, but not un-
ON THE LOADSTONE
59
less the substances are in contact; for quick-
silver does not draw to itself gold or lead from
a distance, but remains fixed in its place.
CHAPTER 39. Of mutually repellent bodies
AUTHORS who have treated of the forces of at-
tracting bodies have discoursed of the powers
of repellent bodies also; and in particular those
who have classified objects in nature according
to sympathy and antipathy. It would seem,
therefore, that we must needs say something
about the strife of bodies among themselves,
lest widespread errors, accepted by all to the
ruin of true philosophy, should extend farther.
They tell us that as like things attract for con-
servation's sake, so unlike things and opposites
repel and drive each other away, as is seen in the
antiperistasis (counteraction) of many bodies;
but it is most potent in plants and animals,
which, as they attract things in affinity and of
kin, so do put away things extreme and disad-
vantageous to themselves. But in other bodies
the same reason does not exist for their coming
together by mutual attraction when they are
separated. Animals take food (as do all things
that live), bring it into their inwards, absorb
their nourishment by means of certain organs
(the vital principle acting and operating). Only
things set before them and adjoining them do
they enjoy through a natural instinct, not things
placed afar; herein there is no exercise offeree,
no movement on the part of those other things;
and therefore animals neither attract bodies nor
repel. Water does not repel oil, as some do
think, for oil floats on water; nor does water re-
pel mud, because when mixed with water it
settles at last. This is a separation of bodies un-
like or not perfectly mixed, because of their
matter; but after they have been separated,
they still remain in conjunction without any
natural strife. Thus, in the bottom of a vessel,
muddy sediment rests quiet, and oil remains on
the top of water, nor is it ordered away. A drop
of water remains whole on a dry surface, nor is
it chased away by the dry. Wrongly, therefore,
do they who discourse of these things impart an
antipathy — antipathic* (/>., a power of repulsion
through opposite passions); for neither is there
in them any repellent force, and repulsion comes
of action not of passion. But these people dearly
love their Greek terms. The question for us is
whether there is any body that drives another
away to a distance without material impetus,
as the loadstone attracts. Now a loadstone does
repel another loadstone; for the pole of one is
repelled by the pole of another that does not
agree naturally with it; driving it, it makes it
turn round so that they may come together
perfectly according to nature. But if a weak
loadstone floating freely in water cannot, on
account of obstacles, readily turn about, then
it is repelled and driven farther away by the
other. All electrics attract objects of every kind;
they never repel or propel. What is told of some
plants (<?.g., of the cucumber, which, when oil
is placed beneath it, moves away) is a material
change from neighbourhood, not a hidden sym-
pathy. But when they show you a candle's flame
that touches a cold solid (as iron) turning to one
side, and pretend that here is antipathy, they
talk nonsense. The reason of this they will see
clearer than light when we come to treat of heat
and what it is. As for Fracastono's belief that a
loadstone may be found that shall repel iron,
in virtue of some principle latent in it that is
opposed to iron, it is without any foundation.
BOOK THIRD
CHAPTER 1. Of direction
IN the foregoing books it has been shown that
a loadstone has its poles, iron also poles, and ro-
tation, and fixed verticity, and finally that load-
stone and iron direct their poles toward the
poles of the earth. But now we have to set forth
the causes of these things and their wonderful
efficiencies known aforetime but not demon-
strated. Of these rotations all the writers who
went before us have given their opinions with
such brevity and indefiniteness that, as it would
seem, no one could be persuaded thereby, while
the authors themselves could hardly be con-
tented with them. By men of intelligence, all
their petty reasonings — as being useless, ques-
tionable, and absurd, and based on no proofs or
premises— are rejected with the result that
magnetic science, neglected more and more and
understood by none, has been exiled. The true
south pole, and not the north (as before our
time all believed), of a loadstone placed on its
float in water turns to the north; the south end
of a piece of magnetized and of unmagnetized
iron also moves to the north. An oblong piece of
iron of three or four finger- breadths, properly
stroked with a loadstone, quickly turns to north
and south. Therefore artificers place such a bar,
balanced on a point, in a compass-box or in a
sun-dial; or they construct a versorium out of
two curved pieces of iron that touch at their
extremities so that the movement may be more
constant; thus is constructed the manner's com-
pass, an instrument beneficial, salutary, and for-
tunate for seamen, showing the way to safety
and to port. But it is to be understood at the
threshold of their argument, before we proceed
farther, that these directions of loadstone or of
iron are not ever and always toward the world's
true poles, that they do not always seek those
fixed and definite points, nor rest on the line of
the true meridian, but that at places, more or
less far apart, they commonly vary either to the
east or to the west; sometimes, too, in certain
regions of land or sea, they point to the true
poles. This discrepance is known as the varia-
tion of the needle and of the loadstone; and as
it is produced by other causes and is, as it were, a
sort of perturbation and depravation of the true
direction, we propose to treat here only of the
true direction of the compass and the magnetic
needle, which would all over the earth be the
same, toward the true poles and in the true
meridian, were not hindrances and disturbing
causes present to prevent: in the book next fol-
lowing we will treat of its variation and of the
cause of perturbation.
They who aforetime wrote of the world and
of natural philosophy, in particular those great
elementarian philosophers and all their progeny
and pupils down to our day; those, I mean, who
taught that the earth is ever at rest, and is, as it
were, a dead-weight planted in the centre of the
universe at equal distance everywhere from the
heavens, of simple uncomplex matter possess-
ing only the qualities of dryness and cold — these
philosophers were ever seeking the causes of
things in the heavens, in the stars, the planets;
in fire, air, water, and in the bodies of com-
pounds; but never did they recognize that the
terrestrial globe, besides dryness and cold, hath
some principal, efficient, predominant poten-
cies that give to it firmness, direction, and
movement throughout its entire mass and down
to its inmost depths; neither did they make in-
quiry whether such things were, and, for this
reason, the common herd of philosophizers, in
search of the causes of magnetic movements,
called in causes remote and far away. Martin-
us Cortesius, who would be content with no
cause whatever in the universal world, dreamt of
an attractive magnetic point beyond the heav-
ens, acting on iron. Petrus Peregrinus holds
that direction has its rise at the celestial poles.
Cardan was of the opinion that the rotation of
iron is caused by the star in the tail of Ursa
Major. The Frenchman Bessard thinks that the
magnetic needle turns to the pole of the zodiac.
Marsilius Ficinus will have it that the loadstone
follows its Arctic pole, and that iron follows the
loadstone, and chaff follows amber: as for am-
ber, why, that, mayhaps, follows the Antarctic
pole: emptiest of dreams! Others have come
down to rocks and I know not what "magnetic
60
ON THE LOADSTONE
61
mountains"! So has ever been the wont of man-
kind: homely things are vile; things from
abroad and things afar are dear to them and the
object of longing. As for us, we are habitants of
this very earth, and study it as cause of this
mighty effect. Earth, the mother of all, hath
these causes shut up in her recesses: all mag-
netic movements are to be considered with re-
spect to her law, position, constitution, vertici-
ty, poles, equator, horizon, meridians, centre,
periphery, diameter, and to the form of her
whole inward substance. So hath the earth been
ordered by the Supreme Artificer and by na-
ture, that it shall have parts unlike in position,
terminal points of an entire and absolute body,
and such points dignified by distinct functions,
whereby it shall itself take a fixed direction. For
like as a loadstone, when in a suitable vessel it is
floated on water, or when it is suspended in air
by a slender thread, does by its native verticity,
according to the magnetic laws, conform its
poles to the poles of the common mother, so,
were the earth to vary from her natural direc-
tion and from her position in the universe, or
were her poles to be pulled toward the rising or
the setting sun, or other points whatsoever in
the visible firmament (were that possible), they
would recur again by a magnetic movement to
north and south, and halt at the same points
where now they stand. But why the terrestrial
globe should seem constantly to turn one of its
poles toward those points and toward Cynosura,
or why her poles should vary from the poles of
the ecliptic by 23 deg. 29 min., with some vari-
ation not yet sufficiently studied by astronomers,
that depends on the magnetic energy. The caus-
es of the precession of the equinoxes and of the
progression of the fixed stars, as well as of
change in the declinations of the sun and the
tropics, are traceable to magnetic forces: hence
we have no further need of Thebit Bencora's
"movement of trepidation," which is at wide
variance with observations.1 A rotating needle
turns to conformity with the situation of the
earth, and, though it be shaken oft, returns still
to the same points. For in far northern climes,
in latitude 70 to 80 deg. (whither in the milder
season our seamen are wont to penetrate with-
out injury from the cold), and in the middle
regions, in the torrid zone under the equinoctial
line, as also in all maritime regions and lands of
the southern hemisphere, at the highest lati-
tudes yet known, the magnetic needle ever finds
its direction and ever tends in the same way
1 Abti 1'Hasan Thibet Ben Korrah, [Thebitius], born
in Mesopotamia A. D. 835-836.
(barring difference of variation) on this side of
the equator where we dwell and in the other,
the southern part, which, though less known,
has been to some extent explored by our sail-
ors: and the lily of the mariner's compass ever
points north. Of this, we are assured by the
most illustrious navigators and by many intel-
ligent seamen. The same was pointed out to me
and confirmed by our most illustrious Neptune,
Francis Drake, and by Thomas Candish [Cav-
endish], that other world-explorer.
Our terrella teaches the same lesson. The
proposition is demonstrated on a spherical load-
stone. Let A, B be the poles; CD, an iron wire
placed on the stone, always tends direct in the
C < o <« D
meridian to the poles A, B, whether the centre
of the wire be in the middle line or equator of
the stone, or whether it be in any other region
between equator and poles, as H,G, F, E. So the
point of a magnetized needle looks north on this
side of the equator: on the other side the crotch
is directed to the south; but the point or lily
does not turn to the south below the equator,
as somebody has thought. Some inexperienced
persons, however, who, in distant regions be-
low the equator, have at times seen the needle
grow sluggish and less prompt, have deemed the
distance from the Arctic pole or from the mag-
netic rocks to be the cause. But they are very
much mistaken, for it has the same power and
adjusts itself as quickly to the meridian as the
point of variation in southern regions as in nor-
thern. Yet at times the movement appears to
be slower, the point on which the compass
needle is poised becoming in time, during a
long voyage, rather blunt, or the magnetized
needle itself having lost somewhat of its ac-
quired force through age or from rusting. This,
too, may be tested experimentally by poising
the versorium of a sun-dial on a rather short-
pointed needle rising perpendicularly out of
the surface of the terrella. The magnetized
needle turns to the poles of the terrella, and
quits the earth's poles; for a general cause that
is remote is overcome by a particular cause
that is present and strong. Magnetized bodies
incline of their own accord to the earth's posi-
62
WILLIAM GILBERT
tion, and they conform to the terrella. Two
loadstones of equal weight and force conform
to the terrella in accordance with magnetic
laws. Iron gets force from the loadstone and is
made to conform to the magnetic movements.
Therefore true direction is the movement of a
magnetized body in the line of the earth's ver-
ticity toward the natural position and unition
of both, their forms being in accord and sup-
plying the forces. For we have, after many ex-
periments in various ways, found that the dis-
posing and ranging of the magnetized bodies
depends on the differences of position, while the
force that gives the motion is the one form com-
mon to both; also that in all magnetic bodies
there is attraction and repulsion. For both the
loadstone and the magnetized iron conform
themselves, by rotation and by dip, to the com-
mon position of nature and the earth. And the
earth's energy, with the force inhering in it as
a whole, by pulling toward its poles and by re-
pelling, arranges in order all magnetic bodies
that are unattached and lying loose. For in all
things do all magnetic bodies conform to the
globe of earth in accordance with the same laws
and in the same ways in which another load-
stone or any magnetic body whatsoever con-
forms to the terrella.
CHAPTER 2. Directive (or versorial) force, which we
call verticity: what it is\ how it resides in the load-
stone; and how it is acquired when not naturally pro-
duced
THE directive force, which by us is also called
verticity, is a force distributed by the innate
energy from the equator in both directions to
the poles. That energy, proceeding north and
south to the poles, produces the movement of
direction, and produces also constant and per-
manent station in the system of nature, and
that not in the earth alone but in all magnetic
bodies also. Loadstone occurs either in a special
vein or in iron mines, for, being a homogenic
earth-substance possessing and conceiving a pri-
mary form, it becomes converted into or con-
creted with a stony body which, in addition to
the prime virtues of the form, derives from dif-
ferent beds and mines, as from different matri-
ces, various dissimilitudes and differences, and
very many secondary qualities and varieties of
its substance. A loadstone mined in this dtbris
of the earth's surface and of its projections,
whether it be (as sometimes found in China)
entire in itself, or whether it be part of a con-
siderable vein, gets from the earth its form and
imitates the nature of the whole. All the inner
parts of the earth are in union and act in har-
mony, and produce direction to north and
south. Yet the magnetic bodies that in the top-
most parts of the earth attract one another are
not true united parts of the whole, but are ap-
pendages and agnate parts that copy the nature
of the whole; hence, when floating free on wa-
ter, they take the direction they have in the
terrestrial order of nature. We once had chisel-
led and dug out of its vein a loadstone 20 pounds
in weight, having first noted and marked its ex-
tremities; then, after it had been taken out of
the earth, we placed it on a float in water so it
could freely turn about; straightway that ex-
tremity of it which in the mine looked north
turned to the north in water and after a while
there abode; for the extremity that in the mine
looks north is austral and is attracted by the
north parts of earth, just as in the case of iron,
which takes verticity from the earth. Of these
points we will treat later under the head of
"Change of Verticity."
But different is the verticity of the inward
parts of the earth that are perfectly united to
it and that are not separated from the true sub-
stance of the earth by interposition of bodies,
as are separated loadstones situated in the outer
portion of the globe, where all is defective,
spoilt, and irregular. Let AB be a loadstone
mine, and between it and the uniform earthen
globe suppose there are various earths and mix-
tures that in a manner separate the mine from
the true globe of the earth. It is therefore in-
formated by the earth's forces just as CD, a mass
of iron, is in air; hence the extremity B of the
mine or of any part thereof moves toward the
north pole G, just as does C, the extremity of
the mass of iron, but not A nor D. But with the
part EF, which comes into existence continu-
ous with the whole and which is not separated
from it by any mixed earthy matter, the case
is different. For if the part EF, being taken out,
were to be floated, it is not E that would turn
ON THE LOADSTONE
to the north pole, but P. Thus, in those bodies
which acquire verticity in the air, C is the south
extremity and is attracted by the north pole G.
In those which come into existence in the de-
trital outermost part of the earth, B is south,
and so goes to the north pole, But these parts
which, deep below, are of even birth with the
earth, have their verticity regulated differently.
For here F turns to the north parts of the earth,
being a south part; and E to the south parts of
the earth, being a north part. So the end C of
the magnetic body CD, situate near the earth,
turns to the north pole; the end B of the agnate
body BA to the north; the end E of the inborn
body EF to the south pole — as is proved by the
following demonstration and as is required by
all magnetic laws.
Describe a terrella with poles A,B; from its
mass separate the small part EF> and suspend
that by a fine thread in a cavity or pit in the
terrella. E then does not seek the pole A but
the pole By and F turns to /4, behaving quite
differently from the iron bar CD] for, there, C,
touching a north part of the terrella, becomes
magnetized and turns to A, not to B. But here
it is to be remarked that if pole A of the terrella
were to be turned toward the southern part of
the earth, still the end E of the solitary part cut
out of the terrella and not brought near the rest
of the stone would turn to the south; but the
end C of the iron .bar would, if placed outside
the magnetic field, turn to the north. Suppose
that in the unbroken terrella the part EF gave
the same direction as the whole; now break it
off and suspend it by a thread, and E will turn
to B and F to A. Thus parts that when joined
with the whole have the same verticity with it,
on being separated take the opposite; for op-
posite parts attract opposite parts, yet this is not
a true opposition, but a supreme concordance
and a true and genuine conformance of mag-
netic bodies in nature, if they be but divided
and separated; for the parts thus divided must
needs be carried away some distance above the
whole, as later will appear. Magnetic bodies seek
formal unity, and do not so much regard their
own mass. Hence the part FE is not attracted
into its pit, but the moment it wanders abroad
and is away from it, is attracted by the opposite
pole. But if the part FE be again placed in its
pit or be brought near without any media in-
terposed, it acquires the original combination,
and, being again a united portion of the whole,
co-operates with the whole and readily clings
in its pristine position, while E remains looking
toward A and F toward #, and there they rest
unchanging.
The case is the same when we divide a load-
stone into two equal parts from pole to pole.
In the figure, a spherical stone is divided into
two equal parts along the axis AB\ hence,
whether the surface AB be in one of the two
parts supine (as in the first diagram), or prone
in both (as in the second), the end A tends to B.
But it is also to be understood that the point B
does not always tend sure to A, for, after the
division, the verticity goes to other points, for
example to F, G, as is shown in Chapter 14 of
this Third Book. LM, too, is now the axis of
the two halves, and AB is no longer the axis;
for, once a magnetic body is divided, the sever-
M
\
B
BA
B
64
WILLIAM GILBERT
al parts arc integral and magnetic, and have
vertices proportional to their mass, new poles
arising at each end on division. But the axis and
poles ever follow the track of a meridian, be-
cause the force proceeds along the stone's meri-
dian circles from the equinoctial to the poles
invariably, in virtue of an innate energy that
belongs to matter, owing to the long and secular
position, and bearings toward the earth's poles,
of a body possessing the fit properties; and such
body is endowed with force from the earth for
ages and ages continuously , and has from its first
beginning stood firmly and constantly turned
toward fixed and determinate points of the
same.
CHAPTER 3. How iron acquires verticity from the
loadstone^ and how this verticity is lost or altered
AN oblong piece of iron, on being stroked with
a loadstone, receives forces magnetic, not cor-
poreal, nor inhering in or consisting with any
body, as has been shown in the chapters on
coition. Plainly, a body briskly rubbed on one
end with a loadstone, and left for a long time
in contact with the stone, receives no property
of stone, gains nothing in weight; for if you
weigh in the smallest and most accurate scales
of a goldsmith a piece of iron before it is touched
by the loadstone you will find that after the
rubbing it has the same precise weight, neither
less nor more. And if you wipe the magnetized
iron with cloths, or if you rub it with sand or
with a whetstone, it loses naught at all of its
acquired properties. For the force is diffused
through the entire body and through its in-
most parts, and can in no wise be washed or
wiped away. Test it, therefore, in fire, that
fiercest tyrant of nature. Take a piece of iron the
length of your hand and as thick as a goose-
quill; pass it through a suitable round piece of
cork and lay it on the surface of water, and note
the end of the bar that looks north. Rub that
end with the true smooth end of a loadstone;
thus the magnetized iron is made to turn to the
north. Take off the cork and put that magne-
tized end of the iron in the fire till it just begins
to glow; on becoming cool again it will retain
the virtues of the loadstone and will show ver-
ticity, though not so promptly as before, either
because the action of the fire was not kept up
long enough to do away all its force, or because
the whole of the iron was not made hot, for the
property is diffused throughout the whole.
Take off the cork again, drop the whole of the
iron into the fire, and quicken the fire with bel-
lows so that it becomes all alive, and let the
glowing iron remain for a little while. After it
has grown cool again (but in cooling it must not
remain in one position) put iron and cork once
more in water, and you shall see that it has lost
its acquired verticity. All this shows how diffi-
cult it is to do away with the polar property
conferred by the loadstone. And were a small
loadstone to remain for as long in the same fire,
it too would lose its force. Iron, because it is
not so easily destroyed or burnt as very many
loadstones, retains its powers better, and after
they are lost may get them back again from a
loadstone; but a burnt loadstone cannot be re-
stored.
Now this iron, stripped of its magnetic form,
moves in a way different from any other iron,
for it has lost the polar property; and though
before contact with the loadstone it may have
had a movement to the north, and after contact
toward the south, now it turns to no fixed and
determinate point; but afterward, very slowly,
after a long time, it turns unsteadily toward the
poles, having received some measure of force
from the earth. There is, I have said, a twofold
cause of direction— one native in the loadstone
and in iron, and the other in the earth, derived
from the energy that disposes things. For this
reason it is that after iron has lost the faculty of
distinguishing the poles and verticity, a tardy
and feeble power of direction is acquired anew
from the earth's verticity. From this we see
how difficultly, and how only by the action of
intense heat and by protracted firing of the iron
till it becomes soft, the magnetic force impres-
sed in it is done away. When this firing has sup-
pressed the acquired polar power, and the same
is now quite conquered and as yet has not been
called to life again, the iron is left a wanderer,
and quite incapable of direction.
But we have to inquire further how it is that
iron remains possessed of verticity. It is clear
that the presence of a loadstone strongly affects
and alters the nature of the iron, also that it
draws the iron to itself with wonderful prompt-
ness. Nor is it the part rubbed only, but the
whole of the iron, that is affected by the fric-
tion (applied at one end only), and therefrom
the iron acquires a permanent though unequal
power, as is thus proved.
Rub with a loadstone a piece of iron wire on
one end so as to magnetize it and to make it
turn to the north; then cut off part of it, and
you shall see it move to the north as before,
though weakly. For it is to be understood that
the loadstone awakens in the whole mass of the
iron a strong verticity (provided the iron rod
ON THE LOADSTONE
be not too long), a pretty strong verticity in
the shorter piece throughout its entire length,
and, as long as the iron remains in contact with
the loadstone, one somewhat stronger still. But
when the iron is removed from contact it be-
comes much weaker, especially in the end not
touched by the loadstone. And as a long rod,
one end of which is thrust into a fire and made
red, is very hot at that end, less hot in the parts
adjoining and midway, and at the farther end
may be held in the hand, that end being only
warm — so the magnetic force grows less from
the excited end to the other; but it is there in
an instant, and is not introduced in any in-
terval of time nor successively, as when heat
enters iron, for the moment the iron is touched
by the loadstone it is excited throughout. For
example, take an unmagnetized iron rod, 4 or 5
inches long: the instant you simply touch with
a loadstone either end, the opposite end straight-
way, in the twinkling of the eye, repels or at-
tracts a needle, however quickly brought to it.
CHAPTER 4. Why magnetized iron ta^es opposite
verticity; and why iron touched by the true north side
of the stone moves to the earth's north, and when
touched by the true south side to the earth's south:
iron rubbed with the north point of the stone does
not turn to the south, nor vice versa, as all writers
on the loadstone have erroneously thought
IT has already been shown that the north part
of a loadstone does not attract the north part
of another stone, but the south part, and that
it repels the north end of another stone applied
to its north end. That general loadstone, the
terrestrial globe, does with its inborn force
dispose magnetized iron, and the magnetic iron
too does the same with its inborn force, produc-
ing movement and determining the direction.
For whether we compare together and experi-
ment on two loadstones, or a loadstone and piece
of iron, or iron and iron, or earth and loadstone,
or earth and iron conformated by the earth or
deriving force from the energy of a loadstone,
of necessity the forces and movements of each
and all agree and harmonize in the same way.
But the question arises, why does iron
touched with loadstone take a direction of
movement toward the earth's opposite pole and
not toward that pole of earth toward which
looked the pole of the loadstone with which it
was magnetized ? Iron and loadstone, we have
said, are of the same primary nature: iron when
joined to a loadstone becomes as it were one
body with it, and not only is one extremity of
the iron altered, but the rest of its parts are af-
fected. Let A be the north pole of a loadstone
to which is attached the tip of an iron pointer:
the tip is now the south part of the iron, because
it is contiguous to the north part of the stone;
the crotch of the pointer becomes north. For
were this contiguous magnetic body separated
from the pole of the terrella or the parts nigh
the pole, the other extremity (or the end which
when there was conjunction was in contact
with the north part of the stone) is south, while
the other end is north. So, too, if a magnetized
needle be divided into any number of parts
however minute, those separated parts will take
the same direction which they had before divi-
sion. Hence, as long as the point of the needle
remains at A, the north pole, it is not austral,
but is, as it were, part of a whole; but when it
is taken away from the stone it is south, be-
cause on being rubbed it tended toward the
north parts of the stone, and the crotch (the
other end of the pointer) is north. The load-
stone and the pointer constitute one body: B
is the south pole of the whole mass; C (the
crotch) is the north extremity of the whole.
Even divide the needle in two at E, and E will
be south as regards the crotch, E will also be
north with reference to B. A is the true north
pole of the stone, and is attracted by the south
pole of the earth. The end of a piece of iron
touched with the true north part of the stone
is south, and turns to the north pole of the stone
A if it be near; if it be at a distance from the
stone, it turns to the earth's north. So when-
ever iron is magnetized it tends (if free and un-
restrained) to the portion of the earth opposite
the part toward which inclines the loadstone
at which it was rubbed. For verticity always
enters the iron if only it be magnetized at either
66
WILLIAM GILBERT
end. Hence all the needle points at B acquire
the same verticity after being separated, but it
is the opposite verticity to that of the pole B
of the stone; and all the crotches in the present
figure have a verticity opposite to that of the
pole £, and are made to move and are seized
by E when they are in suitable position. The
case is as in the oblong stone F//, cut in two at
G, where F and H, whether the stone be whole
or be broken, move to opposite poles of the
earth, and O and P mutually attract, one being
north, the other south. For if in the whole stone
H was south and F north, then in the divided
stone P will be north with respect to H and O,
south with respect to F; so, too, F and H tend
toward connection if they be turned round a
little, and at length they come together. But if
the division be made meridionally, i.e., along the
line of the meridian and not on any parallel cir-
cle, then the two parts turn about and A pulls
B, and the end B is attracted to A, until, being
turned round, they form connection and are
held together. For this reason, iron bars placed
on parallels near the equator of a terrella whose
poles are AB, do not combine and do not co-
here firmly; but when placed alongside on a
meridian line, at once they become firmly
joined, not only on the stone and near it, but at
any distance within the magnetic field of the
controlling loadstone. Thus they are held fast
together at E, but not at C of the other figure.
For the opposite ends Cand Fof the bars, come
together and cohere, as the ends A and B of the
stone did. But the ends are opposite, because
the bars proceed from opposite poles and parts
of the terrella; and G is south as regards the
north pole A, and Fis north as regards the south
pole B. Similarly, too, they cohere if the rod C
(not too long) be moved further toward A, and
the rod F toward #, and they will be joined on
the terrella just as A and B of the divided stone
were joined. But now if the magnetized needle
point A be north, and if with this you touch
and rub the point B of another needle that ro-
tates freely but is not magnetized, B will be
north and will turn to the south. But if with
the north point B you touch still another new
rotatory needle on its point, that point again
will be south, and will turn to the north: a
piece of iron not only takes from the loadstone,
if it be a good loadstone, the forces needful for
itself, but also, after receiving them, infuses
them into another piece, and that into a third,
always with due regard to magnetic law.
In all these our demonstrations it is ever to
be borne in mind that the poles of the stone as
of the iron, whether magnetized or not, are al-
ways in fact and in their nature opposite to the
pole toward which they tend, and that they
are thus named by us, as has been already said.
For, everywhere, that is north which tends to
the south of the earth or of a terrella, and that
is south which turns to the north of the stone.
Points that are north are attracted by the
south part of the earth, and hence when floated
they tend to the south. A piece of iron rubbed
with the north end of a loadstone becomes
south at the other end and tends always
(if it be within the field of a loadstone
and near) to the north part of the load-
stone, and to the north part of the earth
if it be free to move and stand alone at a
distance from the loadstone. The north
pole A of a loadstone turns to the south
of the earth, G; a needle magnetized on
its point by the part A follows A, because
the point has been made south. But the
needle C, placed at a distance from the
loadstone, turns its point to the earth's
north, F, for that point was made south
by contact with the north part of the
loadstone. Thus the ends magnetized by
the north part of the stone become south, or
ON THE LOADSTONE
67
are magnetized southerly, and tend to the
earth's north; the ends rubbed with the south
pole become north, or are magnetized norther-
ly, and tend to the earth's south.
CHAPTER 5. Of magnetizing stones of different
shapes
OF a magnetized piece of iron one extemity is
north, the other south, and midway is the limit
of verticity : such limit, in the globe of the ter-
rella or in a globe of iron, is the equinoctial
circle. But if an iron ring be rubbed at one part
with a loadstone, then one of the poles is at the
point of friction, and the other pole at the op-
posite side; the magnetic force divides the ring
into two parts by a natural line of demarkation,
which, though not in form, is in its power and
effect equinoctial. But if a straight rod be bent
into the form of a ring without welding and uni-
tion of the ends, and it be touched in the mid-
dle with a loadstone, the ends will be both of
the same verticity. Take a ring, whole and un-
broken, rubbed with a loadstone at one point;
then cut it across at the opposite point and
stretch it out straight: again both ends will be of
the same verticity, just like an iron rod magne-
tized in the middle, or a ring not cohering at
the joint.
CHAPTER 6. What seems to be a contrary move-
ment of magnetic bodies is the regular tendence to
union
IN magnetic bodies nature ever tends to union
— not merely to confluence and agglomeration,
but to agreement, so that the force that causes
rotation and bearing toward the poles may not
be disordered, as is shown in various ways in the
following example. Let CD be an unbroken
magnetic body, with C looking toward #, the
B(<f
~B)A
earth's north, B and D toward A, the earth's
south. Now cut it in two in the middle, in the
equator, and then E will tend to A and F to B.
For, as in the whole, so in the divided stone,
nature seeks to have these bodies united; hence
the end E properly and eagerly comes together
again with F, and the two combine, but E is
never joined to D nor F to C, for, in that case,
C would have to turn, in opposition, to nature,
to A, the south, or D to #, the north— which
were abnormal and incongruous. Separate the
halves of the stone and turn D toward C: they
come together nicely and combine. For D tends
to the south, as before, and C to the north ; E and
F, which in the mine were connate parts, are
now greatly at variance, for they do not come
together on account of material affinity, but
take movement and tendence from the form.
Hence the ends, whether they be conjoined or
separate, tend in the same way, in accordance
with magnetic law, toward the earth's poles in
the first figure of the stone, whether unbroken
or divided as in the second figure; and FEof the
second figure, when the two parts come togeth-
er and form one body, is as perfect a magnetic
mass as was CD when first produced in the mine ;
and FE, placed on a float, turn to the earth's
poles, and conform thereto in the same way as
the unbroken stone.
This agreement of the magnetic form is seen
in the shapes of plants. Let AB be a branch of
osier or other tree that sprouts readily; and let
A be the upper part of the branch and B the
part rootward. Divide the branch at CD. Now,
the extremity CD, if skilfully grafted again on
Z), begins to grow, just as B and A, when united
become consolidated and germinate. But if D
be grafted in A, or C on 5, they are at variance
and grow not at all, but one of them dies be-
cause of the preposterous and unsuitable apposi-
tion, the vegetative force, which tends in a fixed
direction, being now forced into a contrary one.
CHAPTER 7. A determinate verticity and a directive
power make magnetic bodies accord, and not an at-
fractional or a repulsative force, nor strong coition
alone or unition
IN the equinoctial circle A there is no coition
of the ends of a piece of iron wire with the ter-
rella; at the poles the coition is very strong. The
greater the distance from the equinoctial the
stronger is the coition with the terrella itself,
and with any part thereof, not with the pole
only. But the pieces of iron are not made to
stand because of any peculiar attracting force
or any strong combined force, but because of
the common energy that gives to them direc-
tion, conformity, and rotation. For in the re-
68
WILLIAM GILBERT
gion B not even the minutest bit of iron that
weighs almost nothing can be reared to the per-
pendicular by the strongest of loadstones, but
adheres obliquely. And just as the terrella at-
tracts variously, with unlike force, magnetic
bodies, so, top, an iron hump (or protuberance
— nasus) attached to the stone has a different
potency according to the latitude: thus the
hump L, as being strongly adherent, will carry
a greater weight than M, and M a heavier
weight than N. But neither does the hump rear
to perpendicular a bit of iron except at the
poles, as is shown in the figure. The hump L
will hold and lift from the ground two ounces
of solid iron, yet it is unable to make a piece
of iron wire weighing two grains stand erect;
but that would not be the case if verticity arose
from strong attraction, or more properly coi-
tion, or from unition.
CHAPTER 8. Of disagreements between pieces of iron
on the same pole of a loadstone; how they may come
together and be conjoined
IF two pieces of iron wire or two needles above
the poles of a terrella adhere, when about to be
raised to the perpendicular they repel each oth-
er at their upper ends and present a furcate ap-
pearance; and if one end be forcibly pushed to-
ward the other, that other retreats and bends
back to avoid the association, as shown in the
B
figure. A and B, small iron rods, adhere to the
pole obliquely because of their nearness to each
other: either one alone would stand erect and
perpendicular. The reason of the obliquity is
that A and B, having the same verticity, re-
treat from each other and fly apart. For if C be
the north pole of a terrella, then the ends A and
B of the rods are also north, while the ends in
contact with and held fast by the pole C are
both south. But let the rods be rather long (say
two finger-breadths), and let them be held to-
gether by force : then they cohere and stand to-
gether like friends, nor can they be separated
save by force, for they are held fast to each oth-
er magnetically, and are no longer two distinct
terminals but one only and one body, like a
piece of wire bent double and made to stand
erect.
But here we notice another curious fact, viz.,
that if the rods be rather short, not quite a
finger's breadth in length, or as long as a barley-
corn, they will not unite on any terms, nor will
they stand up together at all, for in short pieces
of wire the verticity at the ends farthest from
the terrella is stronger and the magnetic strife
more intense than in longer pieces. Therefore
they do not permit any association, any fellow-
ship. Again, if two light pieces of wire, A and
J5, be suspended by a very slender thread of
silk filaments not twisted but laid together,1
and held at the distance of one barley-corn's
length from the loadstone, then the opposite
ends, A and B, situate within the sphere of
influence above the pole, go a little apart for
the same reason, except when they are very
near the pole C of the stone: in that position
the stone attracts them to the one point.
1 Sec Book i, 12.
ON THE LOADSTONE
69
CHAPTER 9. Directional figures showing the varie-
ties of rotation
HAVING now sufficiently shown, according to
magnetic laws and principles the demonstrable
cause of the motion toward determinate points,
we have next to show the movements. On a
spherical loadstone having the poles A, B,
place a rotating needle whose point has been
magnetized by the pole A: that point will be
directed steadily toward A and attracted by A,
because, having been magnetized by A, it ac-
cords truly and combines with A\ and yet it is
said to be opposite because when the needle is
separated from the stone it moves to the oppo-
site part of earth from that toward which the
loadstone's pole A moves. For if A be the north
pole of the terrella, the point of the needle is its
south end, and its other end, the crotch, points
to B: thus B is the loadstone's south pole, while
the crotch of the needle is the needle's north
end. So, too, the point is attracted by EFGH
and by every part of a meridian from the equa-
tor to the pole, because of the power of direct-
ing; and when the needle is in those places on
the meridian the point is directed toward A', for
it is not the point A but the whole loadstone
that makes the needle turn, as does the whole
earth in the case of magnetic bodies turning to
the earth.
The figure following shows the magnetic di-
rections in the right sphere of a loadstone and
in the right sphere of the earth, also the polar
directions to the perpendicular of the poles. All
the points of the versorium have been magne-
tized by pole A. All the points are directed to-
ward A except the one that is repelled by B.
The next figure shows horizontal directions
above the body of the loadstone. All the points
that have been made south by rubbing with the
north pole or some point around the north pole
A, turn to the pole A and turn away from the
south pole B, toward which all the crotches are
directed.
I call the direction horizontal because it co-
incides with the plane of the horizon; for nau-
tical and horological instruments are so con-
structed that the needle shall be suspended or
supported in equilibrium on a sharp point,
which prevents the dip of the needle, as we shall
explain later. And in this way it best serves
man's use, noting and distinguishing all the
points of the horizon and all the winds. Other-
wise in every oblique sphere (whether terrella
or earth) the needle and all magnetized bodies
would dip below the horizon, and, at the poles,
the directions would be perpendicular, as ap-
pears from our account of the dip.
The next figure shows a spherical loadstone
cut in two at the equator; all the points of the
needles have been magnetized by pole A. The
points are directed in the centre of the earth and
WILLIAM GILBERT
between the two halves of the terrella, divided
in the plane of the equator as shown in the dia-
gram. The case would be the same if the divi-
sion were made through the plane of a tropic
and the separation and distance of the two parts
were as above, with the division and separation
of the loadstone through the plane of the equin-
octial. For the points are repelled by C, attrac-
ted by D, and the needles are parallel, the poles
or the verticity at both ends controlling them.
The next figure shows half of a terrella by it-
self, and its directions differing from the direc-
tions given by the two parts in the preceding
figure, which were placed alongside. All the
points have been magnetized by //; all the crot-
ches below, except the middle one, tend not in
a right line but obliquely, to the loadstone, for
the pole is in the middle of the plane that be-
fore was the plane of the equinoctial. All points
magnetized by parts of the loadstone away
from the pole move to the pole (just as though
they had been magnetized by the pole itself)
and not to the place of friction, wherever that
may be in the whole stone at any latitude be-
twixt pole and equator. And for this reason
there are only two differences of regions — they
are north and south as well in the terrella as in
the great globe of earth; and there is no east,
no west place, no regions truly eastern or west-
ern, but, with respect to each other, east and
west are simply terms signifying toward the
east or west part of the heavens. Hence Ptolemy
seems in the Quadripartitum to err in laying out
eastern and western divisions, to which he im-
properly annexes the planets; he is followed by
the rabble of philosophasters and astrologers.
CHAPTER 10. Of the mutation of vertictty and mag-
netic properties, or of the alteration of the force awa-
kened by the loadstone
IRON excited by the magnetic influx has a ver-
ticity that is pretty strong, yet not so stable but
that the opposite parts may be altered by the
friction not only of a stronger but of the same
loadstone, and may lose all their first verticity
and take on the opposite. Procure a piece of
iron wire and with the self-same pole of a load-
stone rub each end equally; pass the wire
through a suitable cork float and put it in the
water. Then one end of the wire will look to-
ward a pole of the earth whereto that end of
the loadstone does not look. But which end of
the wire? It will be just the one that was rub-
bed last. Now rub with the same pole the other
end again, and straightway that end will turn
in the opposite direction. Again rub the end
that first pointed to the pole of the loadstone,
and at once that, having, as it were, obtained its
orders, will go in the direction opposite to the
one it took last. Thus you will be able to alter
again and again the property of the iron, and the
extremity of it that is last rubbed is master. And
now merely hold for a while the north end of the
stone near the north end of the wire that was
last rubbed, not bringing the two into contact,
but at the distance of one, two, or even three fin-
ger-breadths, if the stone be a powerful one;
again the iron will change its property and will
turn to the opposite direction: so it will, too,
though rather more feebly, if the loadstone be
four finger- breadths away. The same results are
had in all these experiments whether you employ
the south or the north part of the stone. Verti-
city can also be acquired or altered with plates
of gold, silver, and glass between the loadstone
and the end of the piece of iron or wire, provid-
ed the stone be rather powerful, though the
plates of metal be touched neither by the stone
nor by the iron. And these changes of verticity
occur in cast-iron. But what is imparted or ex-
cited by one pole of the loadstone is expelled and
annulled by the other, which confers new force.
Nor is a stronger loadstone needed to make the
iron put off the weaker and sluggish force and to
put on a new. Neither is the iron "made drunk-
en" (incbriatur) by equal forces of loadstone, so
that it becomes "undecided and neutral," as
Baptista Porta maintains. But by one same load-
stone, and by loadstones endowed with equal
power and strength, the force is altered, changed,
incited, renewed, driven out. The loadstone
itself, however, is not robbed, by friction with
another bigger or stronger stone, of its property
and verticity, nor is it turned, when on a float,
to the opposite direction or to another pole dif-
ferent from that toward which, by its own na-
ture and verticity, it tends. For forces that are
innate and long implanted inhere more closely,
nor do they easily retire from their ancient
seats; and what is the growth of a long period
of time is not in an instant reduced to nothing
ON THE LOADSTONE
71
unless that in which it inheres perishes. Never-
theless change comes about in a considerable
interval of time, e.g., a year or two, sometimes
in a few months — to wit, when a weaker load-
stone remains applied, in a way contrary to the
order of nature, to a stronger, i.e., with the
north pole of one touching the north pole of the
other, or the south of one touching the other's
south. Under such conditions, in the lapse of
time the weaker force declines.
CHAPTER 11. Of friction of iron with the mid parts
of a loadstone between the poles, and at the equinoc-
tial circle of a terrella
TAKE a piece of iron wire not magnetized, three
finger- widths long (' twill be better if its ac-
quired verticity be rather weak or deforma ted by
some process) ; touch and rub it with the equa-
tor of the terrella exactly on the equinoctial
line along its whole tract and length, only one
end, or both ends, or the whole of the iron, being
brought in to con tact. The wire thus rubbed, run
through a cork and float it in water. It will go
wandering about without any acquired verticity,
and the verticity it had before will be disordered.
But if by chance it should be borne in its waver-
ing toward the poles, it will be feebly held still by
the earth's poles, and finally will be endowed
with verticity by the energy of the earth.
the causes of the magnetic virtue existing in
manufactured iron not magnetized by the load-
stone. The loadstone and iron present and ex-
hibit to us wonderful subtile properties. It has
already oft been shown that iron not excited
by the loadstone turns to north and south; fur-
ther, that it possesses verticity, i.e., distinct
poles proper and peculiar to itself, even as the
loadstone or iron rubbed with the loadstone.
This seemed to us at first strange and incredible:
the metal, iron, is smelted out of the ore in the
furnace, flows out of the furnace, and hardens
in a great mass; the mass is cut up in great
workshops and drawn out into iron bars, and
from these again the smith fashions all sorts of
necessary implements and objects of iron. Thus
the same mass is variously worked and trans-
formed into many shapes. What, then, is it that
preserves the verticity, or whence is it derived ?
First take a mass of iron as produced in the first
iron-works. Get a smith to shape a mass weigh-
ing two or three ounces, on the anvil, into an
iron bar one palm or nine inches long. Let the
smith stand facing the north, with back to the
south, so that as he hammers the red-hot iron
it may have a motion of extension northward;
and so let him complete the task at one or two
heatings of the iron (if needed) ; but ever while
he hammers and lengthens it, have him keep the
CHAPTER 12. How verticity exists in all smelted
iron not excited by the loadstone'
HITHERTO we have declared the natural and
innate causes and the powers acquired through
the loadstone; but now we are to investigate
same point of the iron looking north, and lay
the finished bar aside in the same direction. In
this way fashion two, three, or more, yea one
hundred or four hundred bars: it is plain that
all the bars so hammered out toward the north
and so laid down while cooling will rotate
WILLIAM GILBERT
round their centres and when afloat (being
passed through suitable pieces of cork) will
move about in water, and, when the end is duly
reached, will point north. And as an iron bar
takes verticity from the direction in which it
lies while being stretched, or hammered, or
pulled, so too will iron wire when drawn out to-
ward any point of the horizon between east and
south or between south and west, or conversely.
Nevertheless, when the iron is directed and
stretched rather to a point east or west, it takes
almost no verticity, or a very faint verticity.
This verticity is acquired chiefly through the
lengthening. But when inferior iron ore, in
which no magnetic properties are apparent, is
put in the fire (its position with reference to
the world's poles being noted) and there heated
for eight or ten hours, then cooled away from
the fire and in the same position with regard to
the poles, it acquires verticity according to its
position during heating and cooling.
Let a bar of iron be brought to a white heat
in a strong fire, in which it lies meridionally,
*>., along the track of a meridian circle; then
take it out of the fire and let it cool and return
to the original temperature, lying the while in
the same position as before: it will come about
that, through the like extremities having been
directed toward the same poles of the earth, it
will acquire verticity; and that the extremity
that looked north when the bar, before the
firing, was floated in water by means of a cork,
if now the same end during the firing and the
cooling looked southward, will point to the
south. If perchance the turning to the pole
should at any time be weak and uncertain, put
the bar in the fire again, take it out when it has
reached white heat, cool it perfectly as it lies
pointing in the direction of the pole from which
you wish it to take verticity, and the verticity
will be acquired. Let it be heated again, lying
in the contrary direction, and while yet white-
hot lay it down till it cools; for, from the posi-
tion in cooling (the earth's verticity acting on
it), verticity is infused into the iron and it turns
toward points opposite to the former verticity.
So the extremity that before looked north now
turns to the south. For these reasons and in
these ways does the north pole of the earth give
to that extremity of the iron which is turned
toward it south verticity; hence, too, that ex-
tremity is attracted by the north pole. And
here it is to be observed that this happens with
iron not only when it cools lying in the plane of
the horizon, but also at any inclination thereto,
even almost up to perpendicular to the centre
of the earth. Thus heated iron more quickly
gets energy (strength) and verticity from the
earth in the very process of returning to sound-
ness in its renascence, so to speak (wherein it is
transformated), than when it simply rests in po-
sition. This experiment is best made in winter
and in a cold atmosphere, when the metal re-
turns more surely to the natural temperature
than in summer and in warm climates.
Let us see also what position alone, without
fire and heat, and what mere giving to the iron
a direction toward the earth's poles may do.
Iron bars that for a long time— twenty years or
more— have lain fixed in the north and south
position, as bars are often fixed in buildings and
in glass windows— such bars, in the lapse of
time, acquire verticity, and whether suspended
in air or floated by corks on water turn to the
pole toward which they used to be directed,
and magnetically attract and repel iron in equi-
librium; for great is the effect of long-continued
direction of a body toward the poles. This,
though made clear by plain experiment, gets
confirmation for what we find in a letter written
in Italian and appended to a work by Master
Philip Costa, of Mantua, also in Italian, Of the
Compounding of Antidotes, which, translated, is
as follows: "At Mantua, an apothecary showed
to me a piece of iron completely turned to load-
stone, so attracting other iron that it might be
compared to a loadstone. But this piece of iron,
after it had for a long time supported a terra-
cotta ornament on the tower of the church of
San Agostino at Rimini, was at last bent by the
force of the winds and so remained for ten years.
The friars, wishing to have it restored to its
original shape, gave it to a blacksmith, and in
the smithy Master Giulio Cesare, prominent
surgeon, discovered that it resembled loadstone
and attracted iron. The effect was produced by
long-continued lying in the direction of the
poles. It is well, therefore, to recall what has al-
ready been laid down with regard to alteration
of verticity, viz^ how that the poles of iron bars
are changed when a loadstone simply presents
its pole to them and faces them even from some
distance. Surely in a like way does that great
loadstone the earth affect iron and change ver-
ticity. For albeit the iron does not touch the
earth's pole nor any magnetic portion of the
earth, still the verticity is acquired and altered
—not that the earth's pole, that identical point
lying thirty-nine degrees of latitude, so great a
number of miles, away from this City of Lon-
don, changes the verticity, but that the entire
deeper magnetic mass of the earth which rises
ON THE LOADSTONE
73
between us and the pole, and over which stands
the iron — that this, with the energy residing
within the field of the magnetic force, the mat-
ter of the entire orb conspiring, produces ver-
ticity in bodies. For everywhere within the
sphere of the magnetic force does the earth's
magnetic effluence reign, everywhere does it
alter bodies. But those bodies that are most like
to it and most closely allied, it rules and con-
trols, as loadstone and iron. For this reason it is
not altogether superstitious and silly in many of
our affairs and businesses to note the positions
and configurations of countries, the points of
the horizon and the locations of the stars. For
as when the babe is given forth to the light
from the mother's womb and gains the power
of respiration and certain animal functions, and
as the planets and other heavenly bodies, ac-
cording to their positions in the universe and
according to their configuration with the hori-
zon and the earth, do then impart to the new-
comer special and peculiar qualities; so a piece
of iron, while it is being wrought and length-
ened, is affected by the general cause, the earth,
to wit; and while it is coming back from the
fiery state to its original temperature it be-
comes imbued with a special verticity accord-
ing to its position. Long bars have sometimes
the same verticity at both ends, and hence they
have a wavering and ill-regulated motion on
account of their length and of the aforesaid
manipulations, just as when an iron wire four
feet long is rubbed at both ends with one same
pole of a loadstone.
CHAPTER 13. Why no other bodies save the mag-
netic are imbued with verticity by friction with a load-
stone; and why no body not magnetic can impart and
awaken that force
WOOD floating on water never turns by its own
forces toward the poles of the world save by
chance: so neither threads of gold, silver, cop-
per, zinc, lead, nor glass, when passed through
cork and floated, have ever sure direction; and,
therefore, when rubbed with a loadstone they
show neither poles nor points of variation; for
bodies that do not of their own accord turn to-
ward the poles and are not obedient to the earth
are in no wise governed by the loadstone's
touch; neither has the energy of the loadstone
entrance into their interior, nor are their forms
excited magnetically; nor, if the energy did en-
ter in, could it effect aught, for the reason that
there are no primary qualities in such bodies,
mixed as they are with a variety of efflorescent
humours and degenerate from the primal prop-
erty of the globe. On the other hand the prop-
erties of iron which are primal are awakened by
approach of a loadstone: like brute animals and
men when awakened out of sleep, the proper-
ties of iron now move and put forth their
strength.
Here we must express wonder at a manifest
error of Baptista Porta, who, though he prop-
erly refuses assent to the inveterate falsehood
about a force the opposite of the magnetic, im-
parts a still falser opinion, to wit that iron
rubbed with diamond turns to the north. "If," he
writes, "we rub an iron needle on diamond, and
then put it in a boat or on a straw or suspend it
properly with a thread, at once it turns to the
north like iron rubbed on a loadstone, or per-
haps a little more sluggishly. Nay — and this is
worthy of remark— the opposite part, like the
loadstone itself at its south end, repels iron, and
when we experimented with a multitude of
small iron rods in water, they all stood at equal
distances apart and pointed north." Now this
is contrary to our magnetic rules; and hence
we made the experiment ourselves with seven-
ty-five diamonds in presence of many witnesses,
employing a number of iron bars and pieces of
wire, manipulating them with the greatest care
while they floated in water, supported by corks;
yet never was it granted me to see the effect
mentioned by Porta. He was led astray by the
verticity of the iron in the bars or wires got
from the earth (as shown above); the iron of
itself tended toward its determinate pole, and
Porta, ignorant of this, supposed the thing was
done by the diamond. But let searchers of the
things of nature beware lest they be further
deluded by their own faultily observed experi-
ments, and lest, with errors and blunders, they
throw into confusion the republic of letters.
Diamond is sometimes called siderite, not be-
cause it is ferruginous or that it attracts iron,
but on account of its glister, like that of shin-
ing iron; this brilliance is possessed by the finest
diamonds. On account of this confusion of
names many effects are credited to diamond
that in fact belong to the loadstone siderite.1
CHAPTER 14. The position of a loadstone, now
above, anon beneath, a magnetic body suspended in
equilibrium, alters neither the force nor the verticity
of the magnetic body
THIS point we may not rightly pass by, because
we must correct an error that has lately arisen
out of a faulty observation of Baptista Porta;
out of this erroneous judgment, Porta, by vain
1 Sec Book i. 2.
74
WILLIAM GILBERT
repetition, makes three chapters, viz., the eighth,
the thirty-first, and the sixty-second. Now, if
a loadstone or a piece of iron suspended in
equilibrium or floating in water is attracted or
controlled by another piece of iron or another
loadstone held above it, the stone or the iron
does not turn to the opposite direction when
you apply the second iron or stone beneath; on
the contrary, the ends of the floating loadstone
or of the floating iron will ever turn to the same
points of the stone, however the loadstone or
the iron may be suspended in equilibrium or
whether they be mounted on a point so that
they may revolve freely. Porta was led into
error by the uneven shape of some loadstone or
by the fact that he did not manage the experi-
ment aright. Thus he is badly mistaken, think-
ing it fair to infer that, as the loadstone has a
north and a south pole, it has also an east and a
west, a superior and an inferior, pole. So do
many vain imaginations arise out of mistakes
committed and accepted as true judgments.
CHAPTER 15. The poles \ equator, centre, are per-
manent and stable in the unbroken loadstone; when
it is reduced in size and a part taken away, they vary
and occupy other positions
LET AB be a terrella, E its centre, DF its di-
ameter (and also its equinoctial circle). If you
cut out a piece (for instance along the Arctic
circle) GH, it is evident that the pole which be-
fore was at A now has its seat at /. But the centre
A
and the equinoctial circle recede only toward B,
so as always to be in the middle of the mass
that remains between the plane of the Arctic
circle GIH and the Antarctic pole B. Thus the
segment of the terrella between the plane of
the former equinoctial circle DBF (that is of
the equinoctial circle which existed before the
part was cut away) and the newly acquired
3uator MLN will always be equal to one half
the part cut off, GIHA. But if the part be
cut from the side CD then the poles and the
axis will not be in the line AB but in EF-, and
the axis is changed in the same proportion as
F B
the equator in the previous figure. For these
points of forces and of energy, or rather these
terminals of forces that flow from the entire
form, are moved forward by change of mass or
of figure; as all these points result from the joint
action of the whole and of all the parts united,
and verticity or polarity is not a property in-
nate in the part or in any fixed point, but a
tendency of the force to such part. And as a ter-
rella dug out of the earth has no longer the poles
and the equator of the earth but special poles
and equator of its own, so, too, if the terrella
be cut in two again, these points and distinctions
of its forms and powers migrate to other parts.
But if the loadstone be in any way divided
either on the parallels or on the meridians so
that in consequence of the change of its shape
either the poles or the equator migrate to other
seats, then if the part that has been cut off be
but set in its natural position and conjoined to
the rest, though they be not cemented or other-
wise fastened together, the terminal points go
back again to the former places as though no
part of the body had been cut away. When the
body is whole the form remains whole; but
when the mass of the body is reduced, a new
whole results, and a new wholeness necessarily
arises in each minutest piece of loadstone, even
in magnetic gravel and fine sand.
CHAPTER 16. If the south part of a loadstone have
a part broken off, somewhat of power is taken away
from the north part also
FOR though the south part of magnetic iron is
attracted by the north part of the loadstone,
still the south part of the stone does not reduce
but increases the power of the north part.
Hence if a loadstone be cut and divided at the
Arctic circle, or at the tropic of Cancer, or at
ON THE LOADSTONE
75
the equator, the south part does not so power-
fully attract at its pole as before; for a new
whole arises and the equator leaves its former
place and advances poleward, because of the
division of the stone. In the former state, in-
asmuch as the opposite part of the stone be-
yond the plane of the equator increases the
mass, it also strengthens the verticity and the
force and the movement toward unition.
CHAPTER 17. Of the use of rotary needles and their
advantages; how the directive iron rotary needles of
sundials and the needles of the mariner's compass are
to be rubbed with loadstone in order to acquire
stronger verticity
MAGNETIZED versoriums (or magnetized rotary
needles) serve so many purposes in the life of
man, that it will not be out of place to show the
best process for rubbing and magnetically ex-
citing them and the proper method of apply-
ing the process. With the aid of a small bar of
iron magnetically prepared and suspended in
equilibrium, rich iron ores and those contain-
ing most metal are recognized, and magnetic
stones, clays, and earths, whether crude or pre-
pared, are distinguished. A little iron bar — that
soul of the mariner's compass, that wonderful
director in sea-voyages, that finger of God, so
to speak — points the way and has made known
the whole circle of earth, unknown for so many
ages. Spaniards (and Englishmen too) have
again and again circumnavigated the whole
globe on a vast circle by the help of the mari-
ner's compass. They who travel on land or who
remain at home have sun-dial horologes. The
magnetic needle pursues and searches for veins
of iron in mines: with its help mines are driven
when cities are besieged; cannons and military
engines are trained at night in the desired di-
rections. The needle is of use for topography,
for determining the areas and position of build-
ings, and in constructing underground aque-
ducts. On it depend the instruments invented
for investigating its own dip and its own varia-
tion. When iron is to be quickened by the load-
stone, let it be clean and neat, not disfigured
by rust or dirt, and have it of the best steel. Let
the stone be wiped dry so that there shall be no
moisture, and scrape it gently with some well-
polished iron tool. But beating it with a ham-
mer is of no avail. And let the naked iron be
applied to the naked stone and rubbed at it in
such a way that they may come into closer con-
tact— not in order that the corporeal matter of
the stone may be joined to the stone and stick
to it, but the two are slightly worn away by the
friction, and (useless parts being ground off)
are united closely: hence arises in the excited
iron a grander force. In the figure, A shows the
best mode of applying the versorium to the
stone — its point touches the pole and is directed
toward the pole — B is a passable mode, for
though it is at a little distance from the pole i-
is directed toward it; so, too, C is only a passa
ble mode, the point being turned away from
the pole; D is a worse mode on account of the
greater distance from the pole; F is a bad mode
because it lies on a parallel across the stone; the
magnetic needle L that is rubbed on the equa-
tor is of no value and plainly is negative and
forceless; the oblique indirect mode G and the
oblique indirect averse H are both bad.
The purpose of all this is to show the differ-
ent powers of a globular loadstone. But the ar-
tificers often use a stone rather tending toward
the conical form, and, therefore, more power-
ful, its topmost projection being the pole, at
which they rub the needles. Sometimes, also,
the stone has at the top and above the very pole
an artificial cap or snout of steel to give more
strength; on this cap iron versoriums are
rubbed, and thereafter they turn to that same
pole as though they had been magnetized at
that part without the cap.
The stone should be of good size and strong;
the versorium, even if it be long, must be pretty
thick, not too thin, with moderate-sized point,
not too sharp, though the energy is not in the
point itself but in the whole needle. Any pow-
erful, large loadstone serves well for rubbing
versoriums, though sometimes, owing to its
powerfulness, it causes, when the needle is long,
some dip and perturbation, so that the needle,
that before friction stood in equilibrium in the
plane of the horizon, now, after friction and
excitation, dips with one end as low as the ful-
crum on which it is supported permits. Hence
in the case of a long versorium the end that is
76
WILLIAM GILBERT
to be north should be, before friction, a little
lighter than the other end, so that it may remain
in exact equipoise after friction. But a versori-
um so prepared performs its function poorly at
any considerable distance from the equinoctial
circle.
When the versorium has been magnetized,
put it back in its box, and do not let it come in
contact with other magnetic bodies, nor re-
main in close neighborhood with them, lest it
become unsteady and sluggish through the ac-
tion of opposite forces, whether potent or fee-
ble. And if you rub the other end of the needle
at the opposite pole of the stone, the needle will
act with more steadiness, especially if it be ra-
ther long. Iron rubbed with loadstone keeps
constant and strong, even for several centuries,
the magnetic power awakened in it, if it be
laid in the natural position, meridionally, not
on a parallel, and is not spoilt by rust or any
external ill coming from the ambient medium.
Porta seeks amiss a ratio between loadstone
and iron: a small mass of iron, saith he, cannot
hold a great measure of power, for it is wasted
by the mighty energy of the loadstone. Clearly,
the iron takes to the full its own virtue, though
it weigh only one scruple and the mass of the
loadstone more than 100 Ibs. It is vain also to
make the versorium rather flat at the end that
is rubbed in order that it may become a better
and stronger magnetic body, and that it may
better seize and hold certain magnetic particles,
but few of which can adhere to a sharp point;
for it was Porta's belief that the energy is trans-
mitted and retained by adhesion of particles of
the loadstone, like hairs, whereas these particles
are simply scrapings detached by the iron from
the softer stone; besides, the magnetized iron
points steadily north and south if, after friction,
it be scoured with sand or emery or other ma-
terial, and even though by long-continued fric-
tion its outer parts be ground down and worn
away. In stroking the loadstone with a verso-
rium each stroke should terminate at one end
of the versorium, else, if the stroke is made to-
ward the middle, a less degree of verticity, or
none at all, or very little is excited in the iron.
For where the contact ends there is the pole and
the point of verticity. To produce stronger, ver-
ticity in iron by friction with a loadstone, it is
necessary in northern latitudes to turn the load-
stone's true north pole toward the zenith; on
such pole that end of the versorium is to be
rubbed which afterward will turn to the earth's
north; the other end of the versorium must be
rubbed on the south pole of the terrella turned
toward the earth; so excited, it will incline
to the south. In southern latitudes, below the
equator, the case is different, and the cause of
the difference is given in Book n. 34, where is
shown (by means of a combination of earth and
terrella) why the poles of a loadstone are, for
diverse reasons, one stronger than the other.
If between the ends of two loadstones in con-
junction and equal in power, shape, and mass,
you rub a versorium, it acquires no property.
A, B are two loadstones conjoined naturally at
their opposite ends; C, the point of a versorium,
touched simultaneously by both, is not excited,
if the loadstones be equal (though the load-
stones are connected with it in the natural way) ;
but if the loadstones be unequal, force is gained
from the stronger.
In magnetizing a versorium with a loadstone
begin at its middle and so draw it over the stone
that one end quits the stone last; finally let the
application be continued by a gentle stroking
of the stone with the end of the needle for a
while, say one or two minutes. The movement
from middle to end must not, as is the wont,
be repeated, for so the verticity is spoilt. Some
delay is needed, for though the energy is in-
fused and the iron is excited instantaneously,
still the verticity is more steady and endures
more surely in the iron when the versorium is
left near the loadstone and abandoned at rest
for a proper length of time; although an armed
stone lifts a greater weight of iron than an un-
armed, still a versorium is not more powerfully
magnetized by the armed than by the unarmed
stone. Take two pieces of iron wire, of equal
length, cut off the same coil of wire, and let one
bfe excited by the armed end, the other by the
unarmed end: it will be found that they begin
to move and make a perceptible inclination to-
ward the loadstone at the same distances: this
can be ascertained by measurement with a long
rod. But objects powerfully excited turn quick-
ly to the pole; those that are feebly excited turn
slowly and only when brought nearer: the ex-
periment is made in water with corks of equal
size.
BOOK FOURTH
CHAPTER 1. Of variation
So far we have been treating of direction as if
there were no such thing as variation; for we
chose to have variation left out and disregarded
in the foregoing natural history, just as if in a
perfect and absolutely spherical terrestrial globe
variation could not exist. But inasmuch as the
magnetic direction of the earth, through some
fault and flaw, does depart from the right track
and the meridian, the occult and hidden cause
of variance which has troubled and tormented,
but to none effect, the minds of many has to be
brought to light by us and demonstrated. They
who hitherto have writ ten of the magnetic move-
ments have recognized no difference between
direction and variation, but hold that there is one
only movement of the magnetized needle. But
the true direction is a movement of the mag-
netic body to the true meridian, and continu-
ance therein, with the ends pointing to the re-
spective poles. Yet very oft it happens, afloat
and ashore, that a magnetic needle does not look
toward the true pole, but is drawn to a point
in the horizon nigh to the meridian, and that
there is a deflection not only of the needle and
magnetized iron in general and of the manner's
compass, but also of a terrella on its float, of
iron ore and ironstone, and of magnetic clays
artificially treated; for they often look with
their poles toward points different from the mer-
idian. The variation, then, as observed with the
aid of instruments or of the mariner's compass,
is an arc of the horizon between the intersection
of the horizon by the meridian and the term of
the deflection on the horizon, or the range of
deviation of the magnetized body. This arc var-
ies and is different according to locality. So the
terminus of the variation is commonly assigned
to a great circle — the circle of variation, as it is
called — and a magnetic meridian passing through
the zenith and the point of variation on the
horizon.
In northern terrestrial latitudes this variation
takes place either in the direction from north
toward east, or from north toward west; in
southern latitudes, in like manner, it is from
south toward east, or south toward west. Hence
in northern latitudes we must heed the end of
the needle that tends north, and in southern
latitudes the end looking south: this navigators
and sciolists seldom understand, for on both sides
of the equator they note only the north point
terminal of the compass, or the one that looks
north. As we have already said, every move-
ment of loadstone and needle, every turn and
dip, and their standing still, are effects of the
magnetic bodies themselves and of the earth,
mother of all, which is the fount and source and
producer of all these forces and properties. Thus,
then, the earth is the cause of this variation and
tendence to a different point in the horizon; but
we have to inquire further how and by what
potencies it acts.
Here we must first reject the common opin-
ion of modern writers concerning magnetic
mountains or a certain magnetic rock or a dis-
tant phantom pole of the world controlling the
movement of the compass or of the versorium.
This opinion Fracastorio adopted and developed
after it had been broached by others; but it does
not agree with the experiments at all. For, if it
were correct, in different places on land and sea
the variation point would in geometrical ratio
change to east or to west, and the versorium
would always regard the magnetic pole; but ex-
perience teaches that there is no determinate
pole, no fixed terminus of variation in the globe.
For the arc of variation changes in different
ways erratically, so that in different meridians
and even in the same meridian, and when, ac-
cording to the opinion of recent writers, the
magnetized needle would deviate toward east,
suddenly, on a trifling change of place, it goes
from north toward west, as in the northern re-
gions near Nova Zembla.1 In southern latitudes
also, and at sea, far away from the equator and
toward the Antarctic, and not in northern lati-
tudes near those magnetic mountains, is varia-
tion frequent and great.
But still more vain and silly are the imagina-
tions of other writers — Cortesius, for example,
who speaks of a motive force beyond the far-
1 See Book iv. 16.
77
78
WILLIAM GILBERT
thest heavens; Marsilius Ficinus, who finds the
cause of variation in a star of Ursa; Petrus Per-
egrinus, who finds it in the pole of the world;
Cardan, referring it to the rising of a star in the
tail of Ursa; the Frenchman Bessard, to the pole
of the zodiac ; Livius Sanutus, to a certain mag-
netic meridian; Franciscus Maurolycus, to a
magnetic island ; Scaliger, to the heavens and to
mountains; the Englishman Robert Norman,
to the "respective point."1
Quitting, therefore, those opinions that are
at odds with every-day experience, or that at
least are by no means proven, let us look for the
true cause of variation. The Great Loadstone,
or the terrestrial globe, gives, as I have said, to
iron a north and south direction; magnetized
iron readily conforms itself to those points. But
as the globe of earth is at its surface broken and
uneven, marred by matters of diverse nature,
and hath elevated and convex parts that rise to
the height of some miles and that are uniform
neither in matter nor in constitution but oppo-
site and different, it comes about that this entire
earth-energy turns magnetic bodies at its peri-
phery toward stronger massive magnetic parts
that are more powerful and that stand above the
general level. Wherefore at the outmost super-
ficies of the earth magnetic bodies are turned a
little away from the true meridian. And since
the earth's surface is diversified by elevations of
land and depths of seas, great continental lands,
ocean, and seas differing in every way— while
the force that produces all magnetic movements
comes from the constant magnetic earth-sub-
stance, which is strongest in the most massive
continent and not where the surface is water or
fluid or unsettled— it follows that toward a mas-
sive body of land or continent rising to some
height in any meridian (passing whether through
islands or seas) there is a measurable magnetic
leaning from the true pole toward east or west,
/.?., toward the more powerful or higher and
more elevated magnetic part of the earth's globe.
For as the earth's diameter is more than 1700
German miles, these continents may rise above
the general superficies to a height equal to the
depth of the ocean bed, or more than four miles,
and yet the earth keep the spherical shape, albe-
it slightly uneven at the top. For this reason a
magnetic body under the action of the whole
earth is attracted toward a great elevated mass
of land as toward a stronger body, so far as
the perturbed verticity permits or abdicates its
right. Yet the variation takes place not so much
because of these elevated but less perfect parts
1 See Book 1. 1 ; Book in. 1 ; Book iv. 6.
of the earth and these continental lands, as
because of the inequality of the magnetic
globe and of the true earth-substance which
projects farther in continents than beneath
sea-depths. We have therefore to inquire how
the demonstration of this new natural philo-
sophy may be drawn from unquestionable ex-
periments.
From the coast of Guinea to Cape Verde, the
Canaries, and the frontier of the empire of Mo-
rocco, thence along the coasts of Spain, France,
England, Holland, Germany, Denmark, Nor-
way, the land on the right and to the east is all
continent, vast regions forming one mass; on
the left, immense seas and the mighty ocean ex-
tend far and wide: now we should expect that
(as has in fact been observed by diligent investi-
gators) magnetic bodies would deflect a little
eastward from the true pole toward those more
powerful and extraordinary elevations of the
terrestrial globe. Very different is the case on
the east coasts of North America, for, from the
region of Florida through Virginia and Norum-
bega2 to Cape Race and away to the north, the
needle turns to the west. But in the mid spaces,
so to speak, for example in the western Azores,
it regards the true pole. But it is not on account
of that meridian or of the coincidence of the
meridian with any magnetic pole, as the philos-
ophastric crew suppose, that a magnetic body
turns in like manner to the same regions of the
world ; neither does the variation take place along
the entire meridian, for on the same meridian
near Brazil the case is very different, as later we
will show.
Other things equal, variation is less along the
equator, greater in high latitude, save quite nigh
the very pole. Hence is it greater off the coast of
Norway and Holland than off Morocco or Guni-
ea; greater, too, at Cape Race than in the
ports of Norumbega or of Virginia. In the Guinea
littoral, the magnetized needle inclines to the
east one- third part of a point; in the Cape Verde
Islands two thirds; in England, at the mouth of
the Thames, one point: the higher the latitude
the stronger the moving force, and the masses
of land toward the pole exert most influence :
all this is easily seen in a terrella. For just as,
when the direction is true, magnetic bodies tend
toward the pole (/>., the greater force and the
entire earth co-operating), so do they tend a
little toward the more powerful elevated parts
1 Norumbega, "the lost city of New England." Its site
was indicated as on the bank of the Penobscot, the prov-
ince of that name extending from the Kennebec River to
the St. Croix River.
ON THE LOADSTONE
79
under the action of the whole and in virtue
of the concurrent action of their iron.
CHAPTER 2. That variation is due to inequality
among the earth's elevations
THIS very thing is clearly demonstrated on the
terrella thus: take a spherical loadstone imper-
fect in any part or decayed (I once had such a
stone crumbled away at a part of its surface and
so having a depression comparable to the Atlan-
tic sea or great ocean) ; lay on it bits of iron wire
two barley-corns in length, as in the figure. AB
is a terrella imperfect in parts and of unequal
power on the circumference; the needles E, F
do not vary but regard the pole straight, for
they are placed in the middle of the sound and
strong part of the terrella at a distance from the
decayed part: the surface that is dotted and that
is marked with cross-lines is weaker. Neither
does the needle O vary because it is in the mid-
dle line of the decayed part, but turns to the
pole just as off the western Azores. H and L
vary, for they incline toward the sound parts.
And as this is shown on a terrella whose surface
has sensible imperfections, so, too, in terrellas
that are whole and perfect, for often one part of
a stone is of greater strength on the out-
side than another, though no difference
is plain to sense. With such a terrella
variation is demonstrated and the strong
points are discovered in the following
way: Here A is the pole, B the place of
variation, C the more powerful region.
The horizontal needle at B varies from
the pole C-ward. So is the variation shown and
the regions of greater force recognized. The
more powerful surface is found also by means of
a slender iron wire two barley-corns long: for
though it will stand upright on the pole of the
terrella and in other parts will lean toward the
equator, still if on the same parallel circle it
stands more nearly erect at one point than at
another, the terrella 's surface has more power
where the needle is the more erect; and also
when a piece of iron wire laid on the pole in-
clines more to one side than the other. For ex-
periment take a piece of iron wire three finger-
widths long, resting on the pole A so that its
middle lies over the pole. One of the ends turns
toward C and will not rest in position toward
#; yet, in a terrella that is flawless and even all
over, it will be at rest on the pole no matter to-
ward what point of the equator it be directed.
Or make another experiment: Suppose two
meridians meeting at the poles A, B in equal
arcs DA and CA\ at their extremities D, and C,
let pieces of iron wire be reared: at D (which is
the region of greater force) the wire will be
reared more near perpendicular than at C, the
region of less force. Thus can we discern the
stronger and more powerful part of a loadstone,
else not recognizable by the senses. In a terrella
that is perfect, even, and alike in all its parts,
8o
WILLIAM GILBERT
there is at equal distances from the pole
no variation.
Variation may be shown by means of a ter-
rella having a considerable part of its surface
B
projecting a little above the rest: such terrella,
though not decayed nor spoilt, attracts out of
the true direction, its whole mass operating. The
figure shows a terrella with uneven surface. The
demonstration is made with small bars or short
needles placed on the terrella: they turn from
the terrella toward the projecting mass and the
great eminences. In this way is verticity dis-
turbed on the earth by the great continents
which mostly rise above the beds of the seas
and which at times cause the needle to deviate
from the straight track, i.e., from the true me-
ridian. The tip of the versorium A does not
point toward the pole P if there be a large pro-
jection B on the terrella; so, too, the point C
varies from the pole because of the projection
F. Midway between the two eminences, the
needle G points to the true pole, because, being
equidistant from both projections B and F, it
deviates to neither but keeps the true meridian,
particularly when the energy of the projections
is equal. But elsewhere, at Af, the needle varies
from the pole M toward the eminence H, nor
is hindered nor stayed nor checked by the small
eminence D on the terrella, which is like some
island of the earth in the ocean. But L unhin-
dered tends poleward.
In another mode may variation be shown,
whether in a terrella or on the earth. Let A be
the earth's pole; B its equator; Ca parallel circle
at latitude 30 degrees; D an eminence reaching
poleward; £ another eminence stretching from
the pole equatorward. Evidently the versorium
F in the middle line of D does not vary; but G
deflects very much, G very little as being more
remote from D. So, too, the needle /, placed
directly toward E, does not deflect from the
pole: but L and M turn from the pole toward
the eminence E.
CHAPTER 3. Variation is constant at a given place
As the needle hath ever inclined toward east
or toward west, so even now does the arc of vari-
ation continue to be the same in whatever place
or region, be it sea or continent; so, too, will it
be forevermore unchanging, save there should
be a great break-up of a continent and annihila-
tion of countries, as of the region Atlantis, where-
of Plato and ancient writers tell.
The constancy of the variation and the re-
gard of the versorium toward a fixed point of
the horizon in each region is shown by laying a
very small versorium on a terrella of uneven
surface : the needle always diverges from the me-
ridian over an equal arc. It is shown also by the
inclination of the needle toward a second load-
stone, though in truth this is done by a changed
direction of all within the earth and the terrella.
Lay upon a plane surface a versorium with its
point looking toward A> north; bring alongside
ON THE LOADSTONE
81
the loadstone, B at such distance as to make the
versorium turn to C and no further. Move the
needle of the versorium as often as you will (yet
without stirring either its case or the loadstone)
and the needle will ever surely return to the
point C. Thus if you so hold the stone as to
make the needle turn to E, its point ever returns
to E and not to any other point of the compass.
Just so, by reason of the position of countries
and the differing nature of the uppermost parts
of the earth's globe (certain more magnetic pro-
jections of the terrestrial sphere prevailing), vari-
ation is ever fixed in a given place, but it differs
and is unequal between one place and another,
for the true and polar direction, having its birth
in the entire globe of earth, is slightly diverted
toward particular eminences of great magnetic
force on the broken surface.
CHAPTER 4. The arc of variation does not differ ac-
cording to distance between places
ON the broad ocean, while a ship is borne by
favouring wind along the same parallel, if the
variation be reduced just one degree in a voyage
of 100 miles, it does not follow that the next 100
miles will reduce it another degree. For the
needle varies according to the position and con-
formation of the land and the magnetic force;
also according to distance. For example, when a
ship from the Scilly Islands bound for New-
foundland has proceeded so far that the compass
points to the true magnetic pole, then, as she
sails on, the borrholybic variation begins, but
faintly and with small divergence. But after a
while the arc increases in a higher ratio as equal
distances are traversed, till the ship comes nigh
the continent, when the variation is very great.
Yet before she comes quite to land or enters
port, while at some distance away, the arc is
again lessened a little. But if the ship in her
course departs much from that parallel, either to
north or south, the needle will vary more or less
according to the position of the land and the
latitude of the region; for, other things equal, the
higher the latitude the greater the variation.
CHAPTER 5. An island in ocean does not alter the
variation; neither do mines of loadstone
ISLANDS, albeit they are more magnetic than
the seas, still do not alter magnetic direction nor
variation. For direction being a movement pro-
duced by the energy of the entire earth, and not
due to the attractive force of any prominence
but to the controlling power and verticity of
the whole mass, therefore variation (which is a
perturbation of the directive force), is a wan-
dering from the true verticity and arises out of
the great inequalities of the earth, by reason of
which the earth itself, when very large and pow-
erful magnetic bodies are present, has but little
power of turning away magnetic bodies that re-
volve freely. As for the wonders that some do
report about the island of Elba: loadstones. do
there abound, but, nevertheless, the versorium
(or the mariner's compass) makes no special in-
clination toward it when ships sail by in the Tyr-
rhenian Sea. The reasons already given suffi-
ciently account for this; but, furthermore, a
reason may be found in the fact that the energy
of minor loadstones reaches of itself but little be-
yond their own site; for variation is not pro-
duced by a pulling to, as they would make it
who have thought out magnetic poles. Besides,
mines of loadstone are only agnate, not innate,
in the true earth-substance, and, therefore, the
globe as a whole does not heed them; neither are
magnetic bodies borne toward them, as is proved
in the diagram of prominences.
CHAPTER 6. That variation and direction are pro-
duced by the controlling force of the earth and the ro-
tatory magnetic nature, not by an attraction or a coi-
tion, or by other occult cause
INASMUCH as the loadstone is deemed by the
philosophizers of the vulgar sort to seize and
snatch objects away, as it were, and pretenders
to science have, in fact, noticed no other prop-
erties save this much-lauded force of attraction,
therefore they have supposed that the whole
movement to north and south is produced by
some natural force soliciting bodies. But the Eng-
lishman Robert Norman first strove to show that
this is not done by attraction; he, therefore,
originated the idea of the "respective point"
looking, as it were, toward hidden principles,
and held that toward this the magnetized needle
ever turns, and not toward any attractional
point; but he was greatly in error, albeit he ex-
ploded the ancient false opinion about attrac-
tion. Norman proves his theory as follows: take
a round vessel full of water; on the mid surface
of the water float a small bit of iron wire sup-
82
WILLIAM GILBERT
ported by just so much cork as will keep it afloat
while the water is in equilibrium; the wire must
have been first magnetized so as to show plainly
the variation point D. Let it remain in the water
for a while. Clearly the wire with its cork does
not move toward the rim D of the vessel, as it
would do if attraction came to the iron from Z>,
and the cork would move from its place. This
assertion of the Englishman Robert Norman is
demonstrable, and it does seem to do away with
attraction, inasmuch as the iron remains in the
still water both in the direction toward the very
pole (if the direction be true) and in variation
and irregular direction; and it revolves on its
iron centre, and is not borne toward the vessel's
rim. Yet the direction is not produced by at-
traction, but by a disposing and conversory pow-
er existing in the earth as a whole, not in a pole
or any attrahent part of the stone, neither in
any mass projecting beyond the circle of the
periphery, so that the variation should result
because of the attraction of that mass. Besides,
the directive force of the stone and of iron, and
their natural power of revolving on their centre,
produce the movement of direction and of colli-
mation, in which is included also the motion of
dip or inclination. Nor does the earth's pole at-
tract as though the force of the globe resided in
the pole only: the magnetic force exists in the
whole, but in the pole it is preeminent and sur-
passing. Therefore that the cork abides quietly
in the midst, and that the magnetic needle does
not move toward the rim of the vessel, is a fact
in accord and agreement with the loadstone's
nature, as is shown with the aid of a terrella.
Here a little iron bar, placed on the stone at C,
clings there, nor is it pulled farther away by the
pole A or by the parts near the pole. So, too, it
continues at D and takes direction toward the
pole A, but it sticks at D, and dips also toward
D in virtue of its power of rotation whereby it
conforms itself to the terrella. On this point we
shall treat further when we consider inclination
or the dip of the compass.
CHAPTER 7. Why the variation due to this lateral
cause is not greater than hitherto it has been observed
to be> seldom appearing to amount to two points of
the compass, except near the pole
THE earth, by reason of lateral elevations of the
more energic globe, causes iron and loadstone to
diverge a few degrees from the true pole or true
meridian. For example, here in England, at Lon-
don, it varies 1 1 J^ degrees; in some other places
the variation is somewhat greater, yet in no re-
gion does the end of the needle diverge very
many degrees more from the meridian. For as
the needle always gets its direction from the true
verticity of the earth, so the polar nature of a
continent tends poleward, even as does that of
the whole globe of earth; and though the mass
of a continent may turn magnetic bodies away
from the meridian, still the verticity of that same
land (as of the whole earth also) controls and di-
ON THE LOADSTONE
rects those bodies so that they shall not turn
eastward in too large an arc. It were not easy to
determine according to any general method how
great the arc of variation is in every place, nor
how many degrees and minutes it covers on the
horizon, because it becomes greater or less ac-
cording to divers causes. For we must take ac-
count of the force of true verticity of each place
and of the elevated regions, also of the distances
of those regions from the place under considera-
tion and from the world's poles; and these dis-
tances are to be compared— a thing that cannot
be done with precision. Still, by our method,
the variation is ascertained in such way that no
serious error is left to perturb the course of a
sea-voyage. Were the positions of masses of land
uniform, if the land lay on a meridian line, and
did not present a broken and indented contour,
the variations near the land would be without
complexity, as in the figure.
This is demonstrated with the aid of a long
loadstone whose poles are at the ends A, B: the
middle of the loadstone and the equinoctial is
CD; and the lines GH and EF are meridians on
which are arranged versoriums, the deviations
of which are greater the greater their distance
from the equator. But the inequalities of the
seaboard parts of the habitable globe, the great
promontories, the wide gulfs, the mountainous
and the more elevated regions, and the more un-
even and precipitous regions make the varia-
tions more difficult of determination, and in high
latitudes less certain and more irregular.
CHAPTER 8. Of the construction of the common mar-
iner's compass, and of the different compasses of var-
ious nations
IN a round wooden box (bowl), having its top
covered over with glass, a fly-card (versorium)
rests on a pretty long pin fixed in the middle.
The glass cover keeps out wind and draughts of
air produced by outer causes. All that is within
can be distinctly seen through the glass. The
versorium (rotating part) is circular, made of
light material, as pasteboard, to the under side
of which is attached the magnetized iron or nee-
dle. On the upper side 32 spaces (points as they
are called) are distributed to as many mathe-
matical intervals in the horizon, or winds, which
are distinguished by certain marks and by a lily
indicating the north. The compass-box is sus-
pended in equilibrium in the plane of the hori-
zon, within a ring of brass, which is also pivoted
(equilibrated) in another ring suspended in a
roomy stand, a leaden weight being attached to
the box so that it shall remain in the plane of
the horizon though the ship may be tossed by
the sea in all directions. There are either two
magnetized-iron bars (with ends united) or one
piece of a rather oval shape with the ends pro-
jecting: this style is the surer and quicker of the
two in performing its function. This is to be so
fitted to the pasteboard disk (or card of the com-
pass) that the centre of the disk shall be in the
middle of the magnetized iron. But as variation
begins in the horizon from the point where the
meridian intersects it at right angles, therefore,
on account of the variation, instrument makers
in different countries and cities inscribe the com-
pass variously, and have different ways of at-
taching the magnetized iron to the card where-
on are marked the bounds of the 32 spaces or
points.
There are in general use in Europe four differ-
ent constructions and forms of compass. First,
the form adopted throughout the Mediterran-
ean, and in Sicily, Genoa, and the Venetian re-
public. In all of these compasses the pieces of
iron are so attached beneath to the rotating card
that (where there is no variation) they turn to
the true points of north and south. Hence the
mark for north, designated by a lily, always in-
dicates exactly the point of variation: for the
point of the lily on the card, together with the
ends of the pieces of magnetized iron beneath,
come to a standstill at the point of variation.
Another form of compass is that of Danzig, em-
ployed in the Baltic Sea and in the Netherlands.
Here the magnetized iron underneath diverges
three-fourths of one point eastward from the
lily; for a voyage to Russia the divergence (rec-
ognized difference) is two-thirds. But the com-
passes made at Seville, Lisbon, La Rochelle, Bor-
deaux, Rouen, as well as throughout all England,
have an interval of one-half of a point.
Out of these differences have grown very se-
rious errors in seafaring and in the science of
navigation. For, after the directional positions
of sea-coasts, of promontories, ports, islands, have
been found by the aid of the compass, and the
tides of the seas or the times of full sea have been
determined from the moon's position above one
or another point of the compass (as the phrase
is), we have still to inquire in what country or
according to what country's usage the compass
was constructed by which the directions of said
places and the times of the marine tides were
observed and determined. For the mariner, who,
using British compass, should follow the direc-
tions of the Mediterranean marine charts, must
needs stray far from his true course; so, one who
should use an Italian compass in the North Sea,
84
WILLIAM GILBERT
the German Sea, or the Baltic, in connection
with the marine charts commonly used in those
parts, would oft stray from the right direction.
These differences were introduced by reason of
the unlike variations, that navigators might es-
cape grave errors in those parts of the world.
Yet Petrus Nonius seeks the meridian with a
mariner's compass or versorium (the Spaniards
call it a needle), taking no account of variation;
and he brings forward many geometric proofs
that rest on utterly vicious foundations: for he
had small acquaintance or experience of things
magnetic. In like manner Pedro de Medina, who
does not accept variation, has with many errors
disgraced the art of navigation.
CHAPTER 9. Whether terrestrial longitude can be
found from variation
THAT were a welcome service to mariners and
would advance geography very much. But Por-
ta (vn. 38) is deluded by a vain hope and by a
baseless theory. For he thinks that, in moving
along a meridian, the needle observes order and
proportion, so that the nearer it is to east the
more it will deviate eastward, and, according as
you advance west, the needle takes a westerly
direction: all of which is false as false can be.
Porta thinks he has found a true index of longi-
tude; but he is mistaken. Taking, however, and
assuming for true these premises, he constructs
a large compass showing degrees and minutes for
observing these proportional changes of the nee-
dle. But his principles are erroneous and illogi-
cally taken and very poorly studied; for a ver-
sorium does not vary more to the east because
it is carried to the east; and though in the coun-
tries of western Europe and the seas adjoining
the variation is to the east, and beyond the Azores
it is changed a little toward the west, neverthe-
less variation is in divers ways ever uncertain,
both because of latitude and longitude and be-
cause of approach to great masses of land, also
because of the altitude of dominant terrestrial
elevation; but it does not follow the rule of any
meridian, as we have already shown. Livius San-
utus sorely tortures himself and his readers with
like vanities. As for the opinion of the common
run of philosophizers and mariners, that the me-
ridian which passes through the Azores is the
limit of variation, so that on the opposite side
of that meridian a magnetic body will point to
the poles exactly as at the Azores—an opinion
held also by Joannes Baptista Benedictus and
sundry other writers on the art of navigation
— it is in no wise true. Stevinus (quoted by
Hugo Grotius), in his Portuum itwenicndarum
ratione, distinguishes variation according to mer-
idians. "In the island of Corvo,"1 says he, "the
magnetic pointer indicates the true north, but the
farther one advances thence toward the east the
more will he see the needle 'easting', till he comes
to within one mile of Plymouth on the east, where
the variation, reaching maximum, is 13 deg. 24
min. Then the anatolism (easting) begins to grow
less as far as Helmshud, which place is not far
from North Cape in Finmark: there the north
is pointed to again. There are 60 degrees of long-
itude between Corvo and Helmshud, but the
variation is greatest at Plymouth, whose longi-
tude is 30 degrees." But though these statements
are in part true, still along the entire meridian
of the island of Corvo the compass does by no
means point due north. Neither in the whole
meridian of Plymouth at other places is the var-
iation 13 deg. 24 min., nor in other parts of the
meridian of Helmshud does the needle point to
the true pole. For, on the meridian passing
through Plymouth at lat. 60 deg., the north by
east variation is greater; in lat. 40 deg. it is much
less; in lat. 20 deg. it is very small indeed. On
the meridian of Corvo, though the variation
near the island is nil, yet in lat. 55 deg. the vari-
ation north by west is about J^; in lat. 20 deg.
the variation is % of a point toward the east.
Hence the bounds of variation are not properly
defined by great meridian circles, and far less are
the ratios of increase or decrease toward a given
region of the heavens investigated by that meth-
od. Therefore the rules otclattumen (declining)
or auxanomen (increasing) , anatolism (easting) or
dysism (westing), cannot possibly be found by
that device.Thegroundsofvariationin the south-
ern regions of the earth, which Stevinus there-
after searches into in the same way, are utterly
vain and absurd; they have been put forth by
some Portuguese mariners, but they do not agree
with investigations : equally absurd are sundry
observations wrongly accepted as correct. But
the method of finding the port on long voyages to
distant parts by means of accurate knowledge of
the variation (a method invented by Stevinus
and recorded by Grotius) is of great importance,
if only fit instruments be at hand wherewith the
deviation may positively be ascertained at sea.
CHAPTER 10. Why invarious places near the pole the
variations are much ampler than in lower latitudes
ON the equator or near it, the variation of a
needle is often trifling; not unusually it is null.
In higher latitudes, as 60, 70, 80 degrees, the
1 One of the Azores, the northernmost of the whole
group, lying ten miles north of Florcs.
ON THE LOADSTONE
variations are not infrequently very great. The
reason of this is found partly in the nature of
the earth, partly in the position of the versori-
um. The earth causes magnetic bodies to rotate
and directs them poleward strongly at the equa-
tor; at the poles there is no direction, but only
fast coition of terminals that agree. Hence direc-
tion is weaker at the poles, because the versori-
um, by reason of its tendency to turn to the
pole, dips greatly, and is but feebly directed;
but the force of the lands and eminences is
strong, with an energy proceeding from the en-
tire earth, and, besides, the causes of variation
are nearer: therefore the versorium deflects
more to those eminences. It must be known
also that the direction of a versorium poised
on a needle toward the plane of the horizon is
much stronger at the equator than anywhere
else by reason of the lie of the vers-
orium; and in proportion as latitude in-
creases the direction is less strong, for at
the equator the versorium is directed
naturally toward the plane of the hori-
zon, but in other places it is forced to be
in equilibrium and remains in equilibri-
um because of an external force: by its
nature it dips under the horizon as the
latitude increases, as will be shown in the
Book on Inclination or Dip. Wherefore
direction becomes weaker and at the pole
itself is null. For this reason a weak di-
rection is easily overcome by powerful
causes of variation, and near the pole the
needle deflects more from the meridian.
This is demonstrated with a terrella, on
which is put an iron wire of two finger-
breadths: the wire is quickly and strong-
ly directed toward the poles on a meri-
dian, but in the intervals between equa-
tor and pole it is directed weakly;
herein we may see the great tendency
to variation near the poles.
CHAPTER 11. Cardan's error in seeing to
determine the distance of the earth's centre
from the centre of the world by means of the
loadstone (in his De proportionibus, v)
How very easy it is to make mistakes
and errors in the absence of trustworthy
experiments, while investigating the hid-
den causes of things, is well shown by a
gross blunder of Cardan, who thinks he
has discovered the distances of the cen-
tres of the earth and the world through
the variation of the magnetic needle
over nine degrees; for he believed that
the variation point in the horizon is everywhere
distant eastward nine degrees from due north:
on this basis he establishes a demonstrative ratio
of the different centres.
CHAPTER 12. Of finding the amount of the varia-
tion; what the quantity is of the arc of the horizon
from its arctic or antarctic intersection by a meridian
to the point toward which the needle turns
THE true meridian is the principal basis of the
whole question; when that is surely known it is
easy, with the mariner's compass (when you
know its construction and how the iron bars are
fixed in it), or with any large horizontal versori-
um, to show the arc of variation on the horizon.
A variation compass of good size, after you have
made two observations of the sun before and
after noon, shows the variation by the shadow:
86
WILLIAM GILBERT
the sun's altitude is observed with a radius1 or
with a large quadrant. On account of the great-
er size of the instrument, there is an easier and
surer way of rinding the variation on shore. Get
a thick plank of suitable timber, two feet long,
sixteen inches broad ; on it describe several semi-
circles, as in the accompanying plate, but more
numerous. In the centre erect perpendicularly
a brass stilus; let there be also a rotatory pointer
reaching from the centre to the outermost semi-
circle, and a magnetized versorium in a box with
glass cover. Then when the plank is placed ac-
curately to the level of the horizon by the plane
instrument with its perpendicular, turn the ex-
tremity of the pointer toward the north, so that
the versorium shall rest just on the midline of its
case, which regards the point of variation in the
horizon. Afterwards, at some convenient hour
in the morning— 8 or 9 o'clock—observe the
point of the shadow cast by the stilus when it
reaches the nearest semicircle, and mark with
chalk or ink the place of the shadow's point;
now bring the pointer round to that mark and
note with another mark the number of the de-
gree in the horizon shown by the pointer. In the
afternoon, see when the extremity of the shad-
ow again reaches the periphery of the same semi-
circle, and, bringing the pointer around to the
tip of the shadow, find the degree at the other
side of the lily. From the difference in degrees,
you find the variation: the less being substracted
from the greater, the half of the remainder is
the arc of variation. The amount of variation is
sought to be determined with many other in-
struments and in many other ways, in conjunc-
tion with the mariner's compass— by means of a
globe, number, and by the ratio of triangles and
of sines, the latitude being known and one ob-
servation of the altitude of the sun being made.
But these methods and means are of little ad-
vantage, for it is useless to seek in roundabout
ways and by intricate paths what you may find
more quickly and more surely by taking a short-
er road. The whole trick consists in proper use
of the instruments by which the sun's position
is ascertained readily and quickly (as the sun
does not stand still but moves on), for either
the hand trembles, or the eyesight is defective,
or the instrument does not work aright. Besides,
to observe the sun's altitude on both sides of
the meridian, is as easy as to observe it on one
side only and at the same time to ascertain the
elevation of the pole. And he who can take one
1 Radius astronomicus — measuring-rod, same as radio-
meter. An old instrument for measuring angles; the cross-
stafT; Jacob's-staff; a kind of astrolabe.
altitude with an instrument can take another,
and if the one is doubtful, the whole work with
globe, number, sines, and triangles is thrown
away. Nevertheless, these exercises of mathe-
matical minds are praiseworthy. It is easy for
anyone who stands on the land, by means of ac-
curate observations and with the use of fit in-
struments, to ascertain the variation, especially
in a rather right sphere; but at sea, in view of
the motion and the turning of the waters, ex-
periments cannot be made with exactness as to
degrees and minutes, and, in fact, with the in-
struments in common use, hardly within one
third or one half of a point, particularly in high
latitude: hence so many incorrect and faulty
records of observations by navigators. As for us,
we have contrived a method of finding the vari-
ation, by means of a convenient, handy instru-
ment, from the rising of certain stars, the rising
or setting of the sun, in northern regions, from
the pole-star; for, at sea, when the ship is tossed
by the waves, even the skilled observer deter-
mines the variation more surely with the aid of
a simple instrument and one of no great preci-
sion. Such an instrument is constructed as fol-
lows :
After the pattern of a true and meridional
mariner's compass (with a bare versorium or with
a versorium fastened to a card circle), make an
instrument at least one foot in diameter; divide
its rim into four quarters, each subdivided into
90 degrees. Let the movable compass- box be
balanced below (subtus hbratd) with a heavy
weight of 1 6 pounds. On the edge of the sus-
pended box at beginnings opposite quadrants,
a semicircle rising in the middle to a point (con-
urn) is to be erected (the feet of the semicircle
at both sides being fastened in holes on the mar-
gin) so that the top of the conum shall be per-
pendicular to the plane of the compass; on its
top a rule sixteen digits long is to be fastened at
its middle over the central axis, as it were (of
the com pass- box), like the beam of a balance,
with such a joint that it may move. At the ends
of the rule are small sights with holes through
which we may observe the sun and stars. By
means of the rising or the setting sun at the
equinoxes, the variation can be taken very well
and very readily with this instrument. When
the sun is in other parts of the zodiac, the varia-
tion can also be determined when we have the
altitude of the pole: that known, any one may
find, with a globe, or maps, or with the instru-
ment, the amplitude (of the sun or star) on the
horizon and the distance from the true east as
well of the sun as of the following fixed stars.
ON THE LOADSTONE 87
Then, having counted the degrees and
minutes of the ortive amplitude (time of
rising) from the true east, we readily find
the variation. Observe the foremost star
of the three in Orion's belt when first it
appears on the horizon; direct the instru-
ment toward it, and observe the verso-
rium, for as that star rises in the true east,
generally one degree toward the south,
we can see how far the versorium diverges
from the meridian, allowance made for
that one degree. You may also observe
the Artie pole-star when it is on the meri-
dian or at greatest distance from the meri-
dian (about 3 degrees: according to the
observations of TychoBrahe the pole-star
is 2 deg. 55 min. from the pole), and with
the aid of the instrument you may deter-
mine the variation scientifically, by add-
ing or subtracting the due prostaphaeresis1
of the star's distance from the meridian
(if it is not in the meridian). You will find
when the pole-star is in the meridian, the
sun's place and the hour of the night
being known: even the practised observer
will easily know that without much error,
by the visible inclination of the asterism
— as we do not care for a matter of a few
minutes, as some do, who while striving
to get at the minutes at sea often miss by
a whole point. The experienced observer
will allow somewhat for refraction in not-
ing the rise of the sun or stars, so that
his calculation may be more exact.
1 Prostaphaeresis (Gr. previous subtraction), (i)
The reduction to bring the apparent place of a pla-
net or moving point to the mean place. (2) A me-
thod of computing by means of a table of natural
trigonometrical functions without multiplying.
List of bright, brilliant stars not far from the equator, that can be observed in rising or in
setting from the altitude of the pole and the declination of the stars, the ortive amplitude on
the horizon being ascertained on a globe, or map, or the instrument whence the variation is
determined by artful calculation.
Aldebaran
Bellatrix
Betelgcuze
Mintaka
Sirius
Procyon
Alphard
Pollux
Castor
Regulus
Denebola
Spica
Eye of Taurus
Left shoulder of Orion
Right shoulder of Orion
Foremost star in belt of Orion
Canis Major
Canis Minor
Bright star in Hydra
South head of Gemini
North head of Gemini
Heart of Leo
Tail of Leo
Spica Virginis
Right Ascension
Declination
deg. min.
deg. min.
62
55
15
53
N.
7*
24
4
5
N.
83
30
6
*9
N.
77
46
i
16
S.
97
10
^5
55
S.
109
4'
5
55
N.
'37
10
5
3
S.
no
21
28
3°
N.
107
4
32
10
N.
146
8
*3
47
N.
171
3»
16
30
N.
195
44
8
34
S.
WILLIAM GILBERT
Arcturus and Bootae
Altair
Heart of Aquila
An instrument for finding the ortive amplitude
on the horizon. Describe the periphery of a circle
and divide it into quarters by two diameters in-
tersecting at right angles. One of the diameters
indicates the equinoctial circle, the other the
axis of the world. Divide the four quarters in
the usual way, each into 90 degrees, and to every
fifth or every tenth degree from each end of the
two diameters in both directions assign numbers
on the two margins (outside of this periphery)
provided for the purpose. Then from each degree
draw a right line parallel to the equator. Next
make a rule, or alidade, of the same length as
the diameter of the circle and divided into the
same parts exactly as the diameter which repre-
sents the axis of the world. In the middle of this
rule let a small projecting piece be left attached
whereby the middle of the lineafiducialis1 of the
rule may be connected with the centre of the
Eight Ascension Declination
deg. min. deg, mm.
29 13 21 54 N.
291 56 7 35 N.
circle; and to each fifth or tenth part of the rule
give a number, beginning in the middle and
numbering right and left. The circle represents
the plane of the meridian; its centre represents
the very point of rising or setting, i.e., the inter-
section of horizon and equator. All these lines
equidistant from the equator, represent paral-
lels of the sun and stars; the lineafiducialis of
the rule or alidade represents the horizon, and
its parts degrees of the horizon, beginning at the
point of rising or setting. Therefore, if to the
given latitude of the place, as numbered at each
end of the diameter that represents the axis of
the world, the lineafiducialis of the rule be ap-
1 Fiducial line: (i) The straight edge of the alidade of
a plane table. (2) The initial line of a graduated circle or
vernier. (3) Any line which is intended to be taken as a
standard straight line. The term fiducial, in physics^ de-
notes a fixed position or character, and hence is used as a
basis of refeience or comparison.
ON THE LOADSTONE
plied; and if the given decimation (less the com-
plement of the latitude of the station) of sun or
any star from the equator be found on the rim
of the instrument, then a section of a parallel
drawn from the point of this declination in the
horizon, or in the tinea fiducialis, will show the
ortive amplitude of the given star or of the sun
at the stated latitude of the place.
CHAPTER 13. Observations made by seamen com-
monly vary and are untrustworthy, partly through
mistakes and want of knowledge and the imperfect-
ness of the instruments, and partly because the sea
is seldom so calm but shadows or lights may rest on
the instruments
FROM the time when first the variation of the
needle was noticed, many alert navigators have
in sundry ways striven to investigate the differ-
ence in the direction of the mariner's compass;
but this has not been done with the exactness
that was requisite, much to the disadvantage of
the art of navigation. For, either, being un-
learned, they knew of no sure method, or they
used ill-constructed and unsuitable instruments,
or they adopted some conjecture based merely
on the false hypothesis of some prime meridian
or magnetic pole; while many copy others' writ-
ings and pass off for their own the observations
of earlier writers: and these early authors, how-
ever stupid the writings in which they entered
their observations, are held in high respect just
because of their antiquity; and their posterity
hold it to be not safe to differ from them. Hence
on long voyages, especially to the East Indies,
the inexact records of variation of the compass
kept by the Portuguese are prized; but who-
ever reads what the Portuguese have written
will quickly see that in very many respects they
are mistaken, and that they did not rightly un-
derstand the construction and the use, in taking
the variation of the compass of Portugal (in
which the lily points one-half point west from the
magnetized needle). Hence while they exhibit
the variation of the compass in different places,
it is not certain whether they measure the devi-
ation with a true meridional compass or with
some other kind, in which the magnetized iron
points away from the lily. The Portuguese (as
is seen in their writings) employ the compass of
Portugal, in which the magnetized iron is one-
half of a point to the east of the lily.
Even expert navigators find it very difficult
to observe the variation at sea on account of the
ship's motions and her tossing in every direction,
though they may employ the best instruments
yet devised and in use. Hence have arisen vari-
ous opinions about magnetic deviation. For ex-
ample, the Portuguese navigator Roderigues de
Lazos takes it to be one-half point off the island
of St. Helena; the Dutch, in their nautical jour-
nal, make it one point there; Kendall, an expert
English navigator, makes it only one-sixth of a
point, using a true meridional compass. Diego
Alfonso finds no variation at a point a little
southeast of Cape Agulhas,1 and by the astro-
labe shows that the compass stands in the true
meridian; but Roderigues declares that the com-
pass points due north and south at Cape Agul-
has if it be of the Portuguese style, in which the
variation is one-half point to the southeast.There
is the same degree of confusion, carelessness, and
falsity in most of the other records.
CHAPTER 14. Of the variation under the equinoctial
line and near by
IN northern regions the compass varies because
of the northern eminences; in southern regions
because of the southern eminences; on the equa-
tor, if the eminences on both sides were equal,
there would be no variation. But because this
seldom happens, therefore oftimes variation is
observed under the equator; and even at some
distance from the equator, three or four degrees,
variation may be produced by austral emi-
nences, if extensive and potent austral conti-
nents lie near on one side.
CHAPTER 15. The variation of the magnetized
needle in the great sea, Ethtopic and American, below
the equator
WE have already spoken of the mode and reason
of variation in the great Al tan tic Sea; but below
the equator, on the east coast of Brazil, the nee-
dle swerves toward the continent; with the end
that looks south: thus, at that end, it declines
from the true meridian, toward the west; this is
noticed by navigators as a movement of the
point of the needle, and so they think that the
variation is to the east. But, over the whole
route from the first eastern promontory of Bra-
zil, past Cape Sao Agostino to Cape Frio and as
far as the mouth of the Strait of Magellan, the
variation is always from south to west, the crotch
of the needle tending to the An tar tic pole. For
it always turns with the proper end toward a
continent. Yet the variation takes place not only
on the coast itself, but at some distance from the
land— over a space of 50 or 60 German miles or
more.
But at a great distance from the land the arc
begins to grow less, for the needle turns less to-
1 Southernmost point of Africa.
WILLIAM GILBERT
ward distant prominences; and it is not made to
diverge much by such prominences when pres-
ent and on the spot, for it then shares with them.
On the island of St. Helena (whose longitude is
less than it is usually given in maps) the com-
pass varies one or perhaps two degrees. The Por-
tuguese, and others who have learnt of them, in
sailing beyond the Cape of Good Hope to the
Indies, in order to have favorable winds, shape
their course toward the islands of Tristan de
Cunha, and on the first half of the voyage find
no considerable difference of variation; but near
those islands the difference is greater than any-
where else in the entire voyage. For the great
promontory of the southerly continent which
lies to the southwest pulls and solicits that end
of the versorium which points south (and at
that end is the principal cause of the variation).
But as the ship approaches the Cape of Good
Hope the variation grows steadily less. In the
prime meridian, at latitude 45 degrees, the nee-
dle points southeast by south; and so, too, he
who sails along the coast from Manicongo to the
tropic and a little beyond will find the needle
tending from the south to the southeast, but
not much. At Cape Agulhas it still keeps a little
of the variation it showed near the islands of
Tristan de Cunha, but it is much diminished
owing to the remoteness from the cause of the
variation; and the south end of the needle does
not yet point due south.
CHAPTER 16. Of the variation in Nova Zembla
THE variations are greatest in regions nigh to
the poles, as has been proved, and there, too, the
changes of variation are sudden, as Dutch ob-
servers noted some years ago, though their ob-
servations were not exact; yet the inexactitude
can be excused, for, with the ordinary instru-
ments, it is hard to get at the truth in such high
latitudes—about 80 degrees. But now the vari-
ation of the compass gives the clear evidence of
the existence of an open passage eastward through
the North Sea — Arctic Ocean — for, since the
compass has so great an arc of variation to the
west, it is evident that no continent stretches
for any great distance along that whole route
eastward. Therefore we can strive and explore
more hopefully for a passage to the Moluccas
by the northeast than by the northwest.
CHAPTER 17. Variation in the South Sea
AFTER passing through the Strait of Magellan,
the variation off the Peruvian coast is to the
southeast; and a like deflection continues all
along the coast of Peru to the equator. In higher
latitude, up to 45 degrees, the variation is great-
er than near the equator; and, just as on the
eastern coast of South America, the deflection
was from south toward west, so now it is to the
southeast. From the equator northward the va-
riation is very small or null till you reach New
Galicia; thence along the whole coast as far as
Quivira the inclination is from the north to the
east.
CHAPTER 18. Of the variation in the Mediterranean
Sea
SICILIAN and Italian mariners declare that in
the Sicilian sea and eastward to the meridian of
Peloponnesus (as Francis Maurolycus relates)
the needle grecizes, i.e.9 is diverted from the
pole toward the wind called Graecus (Greek),
or north wind; that on the coast of Peloponne-
sus it points to the true pole; but that when you
proceed farther, then it mistralizes, inclining
from the pole to the mistral or northwest wind :
this is in accordance with our rule of the varia-
tion. For, as the Mediterranean Sea stretches
away from that meridian toward the west, so,
on the side toward the east, there is open sea as
far as Palestine, and toward the north and east
is the whole archipelago, and hard by the Black
Sea. From Peloponnesus to the north pole, that
meridian passes through the largest and most
elevated regions of all Europe: through Achaia,
Macedonia, Hungary, Transylvania, Lithuania,
Livonia, Novgorod, Karelia, and Biarmia.1
CHAPTER 19. The variation in the interior of the
great continents
GREAT seas usually have great variations; in some
parts, however, there is no variation, but true
direction poleward. On the continents, too, the
needle often deflects from the meridian, as on
the margin of the land and the confines, but the
arc of variation is wont to be small: in the mid-
dle regions of great continents there is no varia-
tion. Hence in the heart of northern Europe and
of Asia, in the interior of Africa, Peru, and of
North or Mexican America, the versorium rests
in the meridian.
CHAPTER 20. The variation in the Eastern Ocean
THE variation in the Eastern Ocean, all the way
to Goa and the Moluccas, is noted by the Portu-
guese, but they are mistaken in very many points,
for they follow the first observers who set down
the variations for sundry places, ascertained by
1 The name given by Scandinavian writers to that sec-
tion of northeastern Russia bordering upon the White
Sea.
ON THE LOADSTONE
91
the use of unfit instruments, or by inaccurate
observations, or by conjecture. Thus in the is-
land of Brando1 they make the compass vary 22
degrees to the northwest. Now, in no region, in
no place on earth that has not a higher latitude
than that, is the variation so much as 22 de-
grees: in fact the deviation on that island is tri-
fling. So, when they say that in Mozambique
the compass varies to the northwest one point,
they are in error even though the compass they
use is that of Portugal; for, without a doubt, the
needle varies in Mozambique to the southwest
one quarter of a point or more. Again, they are
all wrong in holding that beyond the equator,
on the route toward Goa, the compass
varies westward one point and one half;
better had they said that in the first
part of the route the compass of Port-
ugal inclines one point, but that a true
or meridional compass varies only
one-half point. Yet to determine the
amount of the variation in the Eastern
Ocean according to our rules, we need a
more exact and correct reconnoissance
of the austral continent, which
stretches farther from the south to-
ward the equinoctial than it is described
in current charts and globes.
CHAPTER 21. How the deviation of the
needle is greater or less according to the dis-
tances of places
IN the heart of great continents there is
no variation; so, too, in the midst of great seas.
On the edge of such lands and seas the variation
is often large, but not as great as it is a little out at
sea: thus off Cape Sao Agostino there is variation,
but 50 miles away to the east there is a larger
variation; still larger 80 miles away and 100 miles
away. But from 100 miles distance the reduc-
tion of the deviation is slower as you approach
the continent than from the distance of 80 miles,
and from 80 miles than from 50; for the devia-
tion is changed and reduced somewhat more
quickly as you come toward the shore from anear
then from afar. So, for mariners approaching
Newfoundland, the change of the variation is
quicker (i.e., a degree of variation is lost in a less
arc of the route on a parallel) when they are not
1 Brando lies in the Gulf of Bothnia, close to the east
coast of Sweden.
far from land than when they are 100 miles
away; but when they journey inland the changes
are more tardy at first than when they come
farther into the interior.
The figure shows the ratio of the arcs on a
parallel circle while a versorium is brought to-
ward a continent that reaches to the pole; the
ratio answers to the degrees of the variation.
Let A be the pole, B the elevation of a great
mass of land. At C there is no variation caused
by B, which is too distant; at D the variation is
greatest, because there the needle is attracted or
is made by the whole earth to turn to the pro-
jecting land B\ nor is the needle hindered, nor
A*
checked, nor led toward the pole by the vertic-
ity of this land, but, tending to the pole, it is
nevertheless deflected therefrom, because of the
site or position and convenient distance of the
overmastering elevations of land.
But, now, from C to D the variation grows,
yet the versorium does not deviate so quickly
in the first stages as it does when near D. But
you sail more miles on the parallel circle CD as
long as you are near C, to register one degree of
variation, than you sail when near Z>; so, too, in
travelling from D toward E you must make a
greater number of miles when near D than when
near E. Thus there are equal deviations for un-
equal distances sailed, both for rising and falling
variation, yet it falls within a less space than it
rises. There are, however several other inciden-
tal cases that confuse this ratio.
BOOK FIFTH
CHAPTER 1. Of the dip of the magnetic needle
WE come at last to that fine experiment, that
wonderful movement of magnetic bodies as
they dip beneath the horizon in virtue of their
natural verticity; after we have mastered this,
the wondrous combination, harmony, and con-
cordant interaction of the earth and the load-
stone (or magnetized iron), being made mani-
fest by our theory, stand revealed. This motion
we have so illustrated and demonstrated with
many experiments, and purpose in what follows
so to point out the causes and reasons, that no
one endowed with reason and intelligence may
justly contemn, or refute, or dispute our chief
magnetic principles. Direction, as also variation,
is demonstrated on the plane of the horizon
whenever a magnetic needle poised in equilib-
rium comes to a rest in any fixed point of it.
But inclination (dip) is seen to be the motion
of the iron bar, first balanced on its axis and
then excited by a loadstone, from that point in
the horizon, one end or pole tending toward
the earth's centre. And we have found that this
inclination differs in the ratio of the latitude of
each region. Now this movement is produced
not by any motion away from the horizon to-
ward the earth's centre, but by the turning of
the whole of the magnetic body to the whole of
the earth, as later we will show. Nor does the
needle descend below the horizon in the ratio
of the degrees of the elevation of the pole in the
given region, and with an equal arc of the quad-
rant in any oblique sphere, as later will be seen.
But how much the needle dips in every horizon
can now first be ascertained by means of an in-
strument (which, however, is not very easily
constructed), just as in sun-dials when the nee-
dle returns to points in the horizon, or as in the
mariner's compass. Get a circular planed board
with diameter at least six finger-lengths, which
is to be fastened to one face of an upright square
post and to rest on a wooden base. Divide the
periphery of the instrument into four quad-
rants, and then each quadrant into ninety de-
grees. In the centre of the instrument drive a
brass nail, and in the centre of its head bore a
small hole well reamed and smoothed. Adjust
to the instrument a circle or ring of brass about
two finger- breadths wide, with a transverse
plate or flat bar of the same metal fastened
across the middle of the ring and serving for
horizon. In the middle of this horizon bar bore
another hole which shall be exactly opposite
to the centre of the instrument, in which a hole
was already bored. Next get a steel wire such as
is used for compass needles, and at the exact
middle of it and at right angles to it pass a very
thin iron axis through it so that the middle of
the axis and the middle of the needle shall ex-
actly meet; let this inclination (dipping) needle,
the ends of the axis having been inserted into
the holes, be suspended so that it may move
freely and evenly on itself in most exact equi-
librium, and so accurately that it may not turn
away from any one degree or point marked on
the circumference more than from any other,
but may rest easily at any one point. Have the
instrument fastened upright to the face of the
post, and on the edge of the base set a very small
magnetized versorium. The needle thus nicely
balanced, now rub skilfully at both ends with
the opposite poles of a loadstone, but do this
with the greatest care lest the wire be in the
least bent ; for unless you do all this with great
skill and dexterity, you will reach no result.
Next get a second brass ring, a little larger than
the first, so as to go round it, and to one rim fit
a cover of glass or of very thin mica; this, when
placed over the other ring, encloses the whole
space, and the needle is protected from dust and
currents of air. The instrument being now com-
plete, set it up perpendicularly with the small
versorium on the base, so that when thus erect-
ed exactly upright it may tend to the true
point of the magnetic direction. Then that one
of the needle's ends which in northern latitudes
looks to the north dips below the horizon; but
in southern latitudes the end of the needle that
looks south tends toward the earth's centre in a
certain ratio (afterward to be explained) of the
latitude of the region in question from the
equator on either side. But the needle must be
rubbed with a powerful loadstone, else it does
ON THE LOADSTONE
93
Dip instrument
not dip at the true point or goes beyond it and is
not always at rest in it. A larger instrument can
also be employed, of tenor twelve finger-lengths
diameter, but in that case there is more trouble
in balancing the needle exactly. Care must be
taken to have the needle of steel, also that it be
straight, and that the sharp points of the axis
on both ends be at right angles with the needle
itself, and that it pass through the very centre.
As in other magnetic movements there is
strict agreement and a clearly visible, sensible
accordance between the earth and the loadstone
in our demonstration, so in this inclination is
the accordance of the globe of the earth and
the loadstone positive and manifest. The true
and definite cause of this great and hitherto
unknown effect is as follows: The loadstone
moves and revolves until one of its poles, being
impelled toward the north, comes to rest in its
predetermined point on the horizon; the pole
that comes to a stand looking north is (as ap-
pears from the foregoing rules and demonstra-
tions) southern, not northern, though till now
every one has supposed it to be northern be-
cause it turns to the north. An iron wire or ver-
sorium touched with this pole of the stone turns
south, and is made northern because rubbed at
the south end of the stone; just as when the
point of a versorium is magnetized in that way
it will be directed toward the earth's south
pole and to that will turn, while the other end,
the crotch, will be southern and will turn to the
northern regions of the earth (the earth itself
causing the motion), for thus does direction re-
94
WILLIAM GILBERT
suit from the bearings of the stone and the nee-
dle, and from the earth's verticity. But inclina-
tion (dip) is when the needle turns to the body
of the earth, its south end pointed to the north,
in any latitude away from the equator. For it
is a fixed and unchanging law that exactly be-
neath the celestial equator, or rather on the
equator of the terrestrial globe, the magnetic
inclination or dip of the needle is nil; and in
whatever way it may have been excited or
rubbed, it rests exactly on the plane of the ho-
rizon in the inclination instrument, provided it
be first duly balanced. The reason of this is, that
the needle, being at equal distance from the two
poles, does not in its rotation dip toward either,
but stands balanced, pointing to the level of
the equator, as it does when mounted on a
sharp point or floating free and unhindered on
water.
But when the needle is in any latitude from
the equator, or when one of the earth's poles
is raised (I do not say raised above the visible
horizon, like what is commonly reputed to be
the pole of the revolving world in the heavens,
but raised above the horizon of the centre or
above its own diameter, equidistant from the
plane of the visible horizon, which is the true
elevation of the earth's pole), then inclination
appears and the needle dips in its meridian to-
wards the body of the earth. Thus, let AB be the
visible horizon of a region; CD the earth's hori-
zon, dividing the earth into equal parts; EF the
earth's axis; G a place within the region: plainly
the north pole E rises above the point C by as
much as G is distant from the equator; there-
fore, since at E the magnetized needle is raised
to perpendicular just by its turning (to the
north), as has already been shown, so now at
G there is a sort of beginning of such a turning,
proportioned to the latitude (the magnetized
body departing from the plane of the horizon),
and the needle intersects at unequal angles the
horizon and shows dip beneath the horizon ; for
this reason, if the dipping needle be placed at
B
G, its south end (that which points north) de-
scends below the plane of the visible horizon
AB. Thus there is very great difference between
a right and a polar or parallel sphere, in which
the pole is in the true zenith. For in a right
sphere the needle is parallel to the plane of the
horizon. But when the celestial pole is in the
vertical point, or when the earth's pole is itself
the place in question, then the needle is perpen-
dicular to the horizon. This is shown on a ter-
rella ; suspend in air, like the beam of a balance,
a small dip needle of only two fingers-width
rubbed at a loadstone, and carefully bring the
terrella under it, and first let the terrella stand
properly as in a right sphere, and, as in the first
of the figures following, the needle will now re-
main in equilibrium. But in an oblique position
of the terrella, as in an oblique sphere and in
the second figure, the needle dips at one end
obliquely toward the neighbouring pole, but does
not rest on the pole, nor is its dip governed by
the pole, but by the whole body and mass; for
the dipping needle in a higher latitude sinks —
passes — beyond the pole. But in the third posi-
tion of the terrella the needle is perpendicular,
because the pole of the stone is uppermost, and
the needle tending straight toward the body
attains the pole. The crotch in the foregoing
figures always turns toward the north pole of
the terrella, having been touched with its north
pole; the point having been touched by the
south pole of the terrella tends toward its south
ON THE LOADSTONE
pole. Thus may we see the level, the oblique,
and the perpendicular position of the needle
on a terrella.
CHAPTER 2. Diagram showing dip of the mag-
netic needle in different positions of a sphere and
horizons of the earth in which there is no variation
of dip
LET AB be the equator, C the Arctic and D the
Antarctic pole, E, G dipping needles in north-
ern regions, and //, F in southern regions of the
earth or the terrella. All the needles have been
touched with the true Arctic pole of the terrel-
la.
The figure shows the needles in horizontal
position at A and B, the earth's and the terrel-
la's equator; they are perpendicular at the poles
C and £>; but in the mid spaces, at distances of
45 degrees, the crotches dip toward the south,
but the points look toward the north at the
same angle.
Diagram showing the direction and dip of a ter-
rella representing the earth relative to the stand-
ard representation of the globe of the earth, at
north latitude 50 degrees.
A is the north pole of the earth or of the large
terrella; B its south pole, C is the smaller terrel-
la, and E the south pole of the smaller terrella
that dips toward the north region (of the larg-
er). Its centre C is placed on the superficies of
the larger terrella, because the smaller terrella
varies a little on account of the length of the
axis, but in the earth the variation is very little.
As the needle dips in the latitude of a region of
50 degrees, so, too, the axis of the stone—which
is spherical — is depressed beneath the horizon,
and its south pole, which is within the circum-
ference of the larger terrella dips, while in the
south (of the larger terrella) its (the smaller
terrella 's) north pole is raised toward the zenith.
And a flat circular piece of iron carefully mag-
netized at opposite points of its circumference
acts in the same way; but these magnetic exper-
iments are less striking because in iron disks the
magnetic force is rather sluggish. The figure be-
low shows, with bits of iron, the differences in
dip at various latitudes in the terrella.
Below is shown the dip of the needle on a ter-
rella by means of a number of bits of iron wire
of equal size, one barley-corn in length, and
placed in a meridian. At the equator the bits of
iron are directed toward the poles, and lie upon
the body of the terrella in the plane of its hori-
zon. The nearer they are placed to the poles the
more do they rise from the horizontal by rea-
son of their turning poleward; at the poles they
tend straight to the centre. But bits of iron will
not stand up aright, save on a good loadstone,
if they be too long.
WILLIAM GILBERT
CHAPTER 3. An instrument for showing by the ac-
tion of a loadstone the degree of dip below the hori-
zon in any latitude
Description of the instrument; its uses
MAKE a perfectly round terrella of a superior
strong loadstone, one homogeneous through-
out, not injured anywhere by decay or corro-
sion, of proper size, so that its diameter shall be
six or seven finger-breadths. Having, by the
method heretofore given, found the poles, mark
them with some iron instrument, also mark the
equinoctial circle. Next, in a squared block of
wood, one foot in diameter, make a hemispheri-
cal cavity to hold half of the terrella, so that
just one half of the terrella shall rise above the
block. Where the limb of the terrella is nearest
the rim of this cavity draw a circle around it
for a meridian, and then divide it into four equal
parts or quadrants, and the quadrants each into
90 degrees. Let one end of the quadrants on the
limb be near the centre of a quadrant on the
block, and divide this also into 90 degrees. At
that centre, place a small short versorium hav-
ing one of its ends sharp and longer than the
other, for use as a pointer, and let it be poised
on a fitting sharp fulcrum. Evidently, whenever
the poles of the terrella are at the beginnings
(zero) of the quadrants, then the versorium will
lie in a right line on the terrella as in equilibri-
ON THE LOADSTONE
97
um. But, if the terrella be moved so that one of
the poles rises on the left, then the needle ele-
vates itself in the meridian according to the lat-
itude, just as a piece of magnetized iron rises;
and the needle indicates upon the quadrant de-
scribed on the block the degrees of the dip. The
rim of the cavity in the block represents a mer-
idian circle, and to it answers some meridian
circle of the terrella, for the poles on both sides
are upon the inner circumference of the rim.
This is precisely what takes place on the earth
itself where there is no variation; but when
there is variation either of direction or of dip,
/>., a disordering of the proper magnetic revo-
lution for causes later to be set forth, then there
is some difference. The quadrant described on
the block must be near the limb of the terrella,
or its centre must be at the limb itself, and the
needle must be very short so as not to touch
the terrella; for there is error when the needle
is long or placed at a distance, as it has a truly
proportionate movement only at the superfi-
cies of the terrella. But were the quadrant — be-
ing remote from the terrella — to be moved into
its sphere of influence toward the pole on a cir-
cle concentric with the terrella, then the needle
would indicate on the quadrant the degrees of
dip in ratio and symmetry with that circle, not
with the terrella.
CHAPTER 4. Of a suitable length of needle on the
terrella for showing the dip
WHEN it is sought to define the dip by means
of a dip-indicating instrument on the earth
itself, we may use either a short verso rium or
one ever so long, provided only the magnetic
property of the loadstone with which it has been
stroked is able to pervade its whole substance
and length. For the greatest length of a ver-
sorium, as compared with the earth's diameter,
is insignificant and has no ratio perceptible by
sense. But on a terrella, or on a plane nigh a
meridian of a terrella, a short needle is required,
one barley-corn's length; for longer versoria
(because they reach farther), in the first degrees
of dip, descend suddenly and irregularly, and
turn to the body of the terrella. For example,
as soon as the long versorium in the figure is
moved onward from the equator A to C, it lays
hold of the stone with its point C as though
with a long outspread wing, when the point
reaches the parts around #, which give it a
greater revolution than those at C. And the
ends of rather long pieces of wire or little rods
are also made to rotate irregularly, just as pieces
of iron wire and iron balls and other spherical
loadstones are made to rotate irregularly by an
oblong loadstone not rounded into a ball. Yet
magnetic bodies or pieces of iron on the surface
of a terrella should not have a long but a very
short axis, so that they may dip true and nat-
urally; for a long versorium situated near a ter-
rella does not easily stand in a right sphere on
the horizon, and wavers and suddenly dips to
one side or the other, especially its magnetized
end, or, if both ends are magnetized, then the
end magnetized last.
CHAPTER 5. That dip is not caused by the attraction
of a loadstone, but by its power of giving direction
and rotation
THROUGHOUT nature we have to recognize that
wondrous work of the Maker whereby the prin-
cipal bodies are restricted within particular lo-
calities and, as it were, hedged round with fences,
nature so ordering. Hence it is that heavenly
bodies do not get confused in their motions and
in their progressions beyond each other. Simi-
larly are the magnetic revolutions produced by
the force of a greater and dominant body as well
as by that of a lesser and subject body, though
that be of very small volume. For the work is
not done by attraction but by incitation on the
part of both, and that with a proportionate
movement toward fixed points beyond which
there is no further motion. For did the versori-
um dip under the action of an attractive force,
then a terrella fashioned out of a very powerful
loadstone would pull it to itself more than
would one made of an indifferent loadstone, and
iron stroked by a strong loadstone would have
greater dip; but that is never so. Further, a
piece of iron attached to and projecting from
the terrella at any latitude does not cause a lit-
tle iron bar to rise more to perpendicular than
does the unarmed stone, though when so armed
the stone does seize and lift far heavier weights.
But if a loadstone be somewhat fashioned to a
point at one end, and rather obtuse at the other,
the acute end or pole solicits with greater force
magnetized iron, the obtuse, thick end makes
the iron turn to itself more powerfully; but a
spherical stone makes it turn to itself power-
WILLIAM GILBERT
fully and in true direction according to mag-
netic laws and the form of spheres; while a
loadstone of some length from pole to pole
stirs the versorium unequally, for in such a stone
the pole of the versorium always is pointed to-
ward the pole of the loadstone itself. So, too, if
the loadstone take a disk shape, with the poles
in the circumference, but with the body plane
and not spherical, when the plane is brought
near to the versorium, the versorium does not
move with the regular magnetic movement as
with a terrella, but turns round always pointing
toward the pole of the loadstone situated in the
circumference of the plane. Besides, if the stone
caused the versorium to revolve by attraction,
then in the first degrees of latitude it would at-
tract toward the mass of the terrella itself the end
of a short versorium; but it does not so attract
as to bring the two together and into coition —
the versorium simply revolves so far as nature
demands, as is shown in the following instance.
For here the point of a versorium in a low
latitude neither touches the stone nor comes in-
to coition with it, only inclines toward it. Fur-
ther, when the versorium rotates as it dips, the
pole of the versorium is not stayed nor held by
the pole of the earth or the terrella, but revolves
regularly, nor remains in any point or terminus
nor looks straight to the pole toward which the
centre of the versorium advances, save at the
pole itself, and that only once between the pole
and the equator; but the inclination goes on
according as the change in the site of the centre
produces a dip in conformity to magnetic laws.
The dip of the needle in water, demonstrated
in the sequel, is also constant: the needle does
not dip toward the bottom of the vessel, but
stands in mid direction poised on its centre ac-
cording to its due dip; yet this would not be
the case if the earth or its poles by attraction
made the extremity of the needle to dip.
CHAPTER 6. Of the ratio of dip to latitude and the
causes thereof
WE have spoken of the construction of the in-
strument for determining the dip, of the causes
and modes of the dip, and of the different in-
clinations of the needle for different localities;
of the inclination of the loadstone, too, and of an
instrument for showing the power of the stone
at any latitude, as well as of the demonstrated
rotation (by erection) of pieces of iron on a
meridian of the stone, according to latitude. We
have now to treat more at length of the causes
of this proportionate inclination. A loadstone
and a piece of iron wire, when moved in a me-
ridian from the equator to the pole, turn toward
a spherical loadstone, and toward the earth also,
with a circular motion. In a right horizon (as
also upon the equinoctial circle of the stone)
the axis of the iron, which is its middle, is a line
parallel with the earth's axis. When that axis
reaches the pole, which is its centre, it stands
still in the same right line with the earth's axis.
The same end of the iron that at the equator
points south turns to the north; for it is not a
movement of centre to centre, but of one mag-
netic body to another, and a natural turning of
the axis of the body to the axis of the terrella,
not caused by the pole's attraction, so that the
iron should regard the earth's polar point. On
the equator the magnetic iron stands in hori-
zontal equilibrium, but toward the pole on ei-
ther side of the equator, at every latitude from
the beginning of the first degree even to the
90 th, it dips; yet, not in ratio to the number of
degrees or the arc of the latitude does the mag-
netic needle dip so many degrees or over a like
arc; but over a very different one, for this move-
ment is in truth not a dipping movement, but
really a revolution movement, and it describes
an arc of revolution proportioned to the arc of
latitude. Hence the magnetic body A, while it
passes round the earth, or an earthkin or terrel-
la, from the equinoctial circle G toward B (the
pole), rotates on its centre, and, midway in its
progress from the equator to pole #, points to
the equator F as the mean of the two poles:
therefore ought the versorium to rotate much
more quickly than the centre travels in order
ON THE LOADSTONE
99
to regard the point F in a right line by rotating.
For this reason the movement of this rotation is
quick in the first degrees from the equator, from
A to L, but slower in the subsequent degrees,
from L to B, that is, with reference to the equa-
torial point T7, toward C. But were dip equal to
the latitude, i.e., always so many degrees from
the horizon as the centre of the versorium has
gone away from the equator, then the magnetic
needle would obey the potency and the peculiar
virtue of the centre as a point operating of it-
self; but it obeys the whole and its mass and
outer limits, the powers of both co-operating,
to wit, those of the magnetized versorium and
of the earth.
CHAPTER 7. Explanation of the diagram of the ro-
tation of magnetized iron
LET ACDL be the body of the earth or of a ter-
rella, M the centre, AD the equator, CL the
axis, AB the horizon, which changes according
to the locality. From the point Fin the horizon,
B
at a distance from the equator A equal to the
semi-diameter CM of earth or terrella, is de-
scribed an arc to //as terminus of the quadrants
of dip: for all quadrants of dip that belong (in-
serviuni) to the parts between A and C begin at
that arc and terminate in the earth's centre, M.
The semi-diameter of this arc is a chord drawn
from the equator A to the pole C. And a line
equal to that chord, drawn in the horizon to B,
gives the starting point of the arc of the termini
of the arcs of revolution and rotation, which arc
is continued on to G. For as the quadrant of a
circle around the earth's centre (the starting-
point of it being in the horizon, at a distance
from the equator equal to the earth's semi-
diameter) is the terminus of all the quadrants of
dip produced from every horizon to the centre,
so a circle round the centre from the starting
point of the first arc of rotation B to G is the
terminus of the arcs of rotation. Between the
arc of rotation BL and BG are intermediate
arcs of revolution and rotation of the magnetic
needle. The centre of the arc is the region or
place where the observation is obtained; the
beginning of the arc is taken from the circle
that is terminus of the revolutions, and it ends
at the opposite pole, as from O to L, in 45 de-
grees latitude. Divide any arc of revolution into
90 equal parts from the terminus of the arcs of
revolution to the pole; for whatever the degree
of latitude of the place, that part of the arc of
revolution is to be reckoned as
cognominal to it which the mag-
netic pole in rotating upon or
around terrella or earth regards:
in the large diagram that fol-
lows, this is indicated by the
right lines. In the middle lati-
tude of 45 degrees the magnetic
rotation is directed to the equa-
tor, and there also the arc from
its terminus to the pole is the
quadrant of a circle; but at lati-
tudes above this (i.e., nearer the
equator) all the arcs of revolu-
tion are greater than a quadrant ;
in latitudes below this (/.<?.,
higher, farther from the equa-
tor) they are less: in the former
the needle rotates quickly; in
the latter it gradually rotates
more slowly. Each region has its
own arc of revolution, in which
is, according to the number of
the degree of latitude of the
place, the terminus toward
which the needle turns; so that a right line drawn
from the region to a point in that arc cognomi-
nal to the number of the degree of latitude in-
dicates the magnetic direction, and shows the
degree of the inclination at the intersection of
the quadrant of dip that belongs to the given
region. Take away the arc of the quadrant of
dip from the centre to the line of magnetic di-
rection, and what remains is the arc of dip be-
100
neath the horizon. Thus, in the rotation of the
versorium N, whose line of magnetic direction
extends to D, take away from the quadrant of
dip SM its arc RM, and what remains will be
the arc of dip, that is, it shows how much the
needle dips in latitude 45 degrees.
CHAPTER 8. Diagram of the rotation of magnet-
ized iron, showing the magnetic dip in all latitudes,
and showing the latitude from the rotation and dip
IN the foregoing diagram, around the body of
the earth or of the terrella are drawn a circle of
rotation and a circle of dip, together with a
first, a last, and a middle arc of rotation and dip.
Now from each one fifth part of that arc which
terminates all the arcs of rotation (and each of
which also is supposed to be divided into 90
WILLIAM GILBERT
equal parts) are drawn arcs to the pole, and from
every fifth degree of the arc terminating the
quadrants of dip are drawn quadrants to the
centre, and at the same time is drawn a spiral
line indicating (by the aid of a movable quad-
rant) the dip in every latitude. Right lines of
magnetic direction are drawn from the degrees
marked on the meridian of earth or terrella to
their proper arcs and to the parts answering to
those arcs.
How to ascertain the elevation of the pole, or
the latitude of any place, by means of the follow-
ing diagram, turned into a magnetic instrument, in
any part of the world, without the help of the heav-
enly bodies, sun, planets, or fixed stars, and in fog-
gy weather as well as in darkness
L
ON THE LOADSTONE
We can sec how far from idle is the magnetic
philosophy; on the contrary, how delightful,
how beneficial, how divine! Seamen tossed by
the waves and vexed with incessant storms,
while they cannot learn even from the heaven-
ly luminaries aught as to where on earth they
are, may with the greatest ease gain comfort
from an insignificant instrument, and ascertain
the latitude of the place where they happen to
be. With a dip instrument an observation is
taken of the degree of the needle's dip beneath
the horizon; that degree is noted on the inside
arc of the quadrant, and the quadrant is turned
round at the centre of the instrument until that
degree on the quadrant touches the spiral line:
then in the open space J5, at the centre of the
quadrant, the latitude of the region on the pe-
riphery of the globe is found by the lineafiduciae
AB. Draw the diagram on a suitable planed
board, and to its centre attach the centre of the
angle of the quadrant A, so that the quadrant
may rotate on that centre. But it must be re-
membered also that in some places there is var-
iation in dip for the causes aforesaid (albeit the
variation is not great): this variation also it will
be well to study, and to account for on some
probable hypothesis, and it will be of very great
interest to observe it in different localities, for
this variation of dip seems to present more diffi-
culty than the variation of direction; but it is
readily understood with dip instruments when
101
it disagrees either by plus or by minus with the
diagram.
Observing the magnetic dip at sea
Place the dip instrument upon our variation
instrument, a wooden ball being put between
the round movable compass-box and the dip
instrument; but first remove the versorium,
lest it interfere with the dip instrument. In this
way, when the sea is in commotion the com-
pass-box will remain erect on the level of the
horizon. The dip compass is to be directed, by
means of a small versorium at its base,
to the point of the variation, to the
greater circle of which (commonly
called the magnetic meridian) the
plane of the upright compass con-
forms; thus the dip instrument, in vir-
tue of its property of rotating, shows
the degree of the dip.
In a dip instrument the magnetic nee-
dle which when on a meridian circle de-
scends^ hangs perpendicular when it lies
on a parallel.
The magnetic needle, in due posi-
tion, while it conforms itself to the
earth in virtue of its rotatory property,
dips in an oblique sphere to a certain
extent. But when the plane of the in-
strument is removed from the plane
of the meridian, the needle (which
tends poleward) no longer remains in
the degree of its dip, but inclines more
toward the centre, for the directional
force is greater than that of the dip;
and all power of dip is taken away if the
plane of the instrument be on a parallel. For then
the needle, its axis being transverse, cannot take
its due position, and so tends perpendicular to
earth, and remains only in its own meridian,
or in what is commonly called the magnetic
meridian.
CHAPTER 9. Demonstration of direction, or of vari-
ation from the true direction, together with dip,
simply by the movement in water, due to the power of
controlling and rotating
PASS through a round cork three finger-breadths
of thin iron wire, so that the cork may support
the iron in water. Let the water be contained in
a vase or large goblet of glass. With a very sharp
knife pare the cork away gradually (still pre-
serving its rotundity) till it will stand a finger-
breadth or two under the surface motionless,
with the wire evenly balanced. Then stroke one
102
WILLIAM GILBERT
end of the wire on the north pole of a loadstone,
the other end on the south pole (very carefully,
so that the cork may not be moved ever so little
out of its place), and put the instrument again
in the water. The wire will dip with a circular
movement on its centre below the plane of the
horizon, according to the latitude of the place,
and even as it dips will show (the true direction
being disordered) the point of variation. The
loadstone with which it is rubbed should be a
powerful one, such as is required in all magnetic
demonstrations. When the wire having been thus
put in the water, and treated with the load-
stone, comes to a standstill in the line of the dip,
its lower end remains in the point of variation
in an arc of a great circle, or meridian, passing
through the zenith and the point of variation in
the horizon, and through that lowermost point
of the heavens called nadir: all this is demon-
strated by bringing a rather long magnetized
needle near the vessel on one side. This is
a demonstration of the absolute conforming
of a magnetic body to unity with the earth's
body; here in the natural way is manifested
direction with variation thereof and dip. But
it is to be understood that delicate and diffi-
cult as this experiment is, so it does not con-
tinue, for the apparatus does not remain in
the midst of the water, but at last sinks to the
bottom when the cork has taken in too much
water.
CHAPTER 10. Of variation of dip
WE have already spoken of direction and of va-
riation as a sort of derangement of direction.
Now we observe a like irregular movement in
the dip, when it descends beneath the limits or
when, as sometimes happens, it does not reach
its due bounds. Thus the variation of the dip is
an arc of the magnetic meridian betwixt the
true and the apparent dip. For as, because of
elevations of the earth magnetized bodies are
pulled to one side, so, too, the needle (its rota-
tion being a little increased) dips beyond the
due measure. And as variation is a deviation in
direction, so, for the same reason, there is some
error of dip, albeit usually a trifling one. Some-
times, too, though there be no variation of di-
rection on the horizon, there may nevertheless
be a variation of the dip, to wit, when either in
a direct meridian line, i.e., on the meridian it-
self, there projects some magnetically powerful
earthmass, or when such elevations have less
force than is called for by the general constitu-
tion of the globe, or when the energy is over-
concentrated in one part, and in another is dif-
fused, as we may see in the Atlantic Ocean. And
this discrepancy of constitution, this variance of
effect, we easily recognize in certain parts of
every spherical loadstone. The inequality of force
in the various regions of a terrella is shown by
the conclusive experiment described in Chapter
2 of this Book. And the effect is clearly shown
by the demonstrational instrument, an account
of which is contained in Chapter 3 of the same
Book.
CHAPTER 11. Of the formal magnetic act spherical-
ly effused
REPEATEDLY we have spoken of the poles of
earth and terrella and of the equinoctial circle;
last we treated of the dip of magnetized bodies
earthward and terrellaward, and the causes
thereof. But having with divers and manifold
contrivances laboured long and hard to get at the
cause of this dip, we have by good fortune dis-
covered a new and admirable science of the
spheres themselves — a science surpassing the
marvels of all the virtues magnetical. For such
is the property of magnetic spheres that their
force is poured forth and diffused beyond their
superficies spherically, the form being exalted
above the bounds of corporeal nature; and the
mind that has diligently studied this natural
philosophy will discover the definite causes of
the movements and revolutions. The potencies
of a terrella, too, are of the same kind through-
ON THE LOADSTONE
out the whole sphere of its influence, and the
spheres (of influence) themselves, at whatever
distance from the body of the terrella, have, in
the ratio of their diameter and the quantity of
their superficies, termini of their forces, or, in
other words, there are points whereat magnetic
bodies turn toward them; and these bodies do
not regard the same part or point of the terrella
at every distance whatever therefrom (unless
they be in the axis of the spheres and the terrel-
la), but ever do tend toward those points of the
spheres (of influence) which are equal arcs dis-
tant from their common axis. Thus in the fol-
lowing diagram we show the body of a terrella,
the air or water took them on or were by them
informated; for the forms are only effused and
really subsist when magnetic bodies are present:
hence the magnetic body within the forces and
limits of the spheres is taken hold of, and in the
several spheres magnetic bodies control other
bodies magnetical and excite them even as
though the spheres of influence were solid ma-
teriate loadstones; for the magnetic force does
not proceed through the whole of the medium,
nor exists really as in a continuous body ; and so
the spheres are magnetical, and yet are not real
spheres existing by themselves.
AB is the axis of a terrella and its spheres; CD
Diagram of the movements in the magnetic spheres.
with its poles and equator; also a magnetic nee-
dle in three other concentric spheres around the
terrella and at some distance therefrom. In these
spheres (and they may be imagined as infinite)
the magnetic needle or versorium regards its
own sphere in which it is placed and its diameter,
poles, and equator, not those of the terrella; and
it is by these and in accordance with the magni-
tude of these that it is made to rotate and is
directed, both while its centre stands still and
while it advances in any arc whatever of that
sphere. Still we do not mean that the magnetic
forms and spheres exist in the air, or water, or
any other medium not magnetical, as though
the equator. In all the spheres, as on the terrella,
at the equator the versorium lies in the plane of
the horizon; in the axis it everywhere regards
the centre perpendicularly; in the mid spaces,
E regards D, and G regards //, not F, which is
regarded by the versorium L on the superficies
of the terrella. But as is the proportion of L to
F on the terrella 's superficies, such is that of G
to H in its own sphere, and of E to D in its own
sphere; so all the revolutions in the spheres to
the termini of the spheres are such as are the
revolutions at the surface of the terrella or to
its termini. But if in the more distant spheres
there is now and then some error, that is to be
104
WILLIAM GILBERT
charged to the inertia of the loadstone or to
weakened power, because of the too great dis-
tance of the spheres from the terrella.
Demonstration
Upon the instrumental diagram above de-
scribed, place a small board or a strong disk of
brass or tin on which are inscribed the magnetic
spheres, as in the diagram; and in the middle
make a hole proportioned to the size of the ter-
rella, so that the board may lie evenly on the
middle of it along the meridian circle above the
wood. Then in one of the spheres of influence
place a small versorium one barley-corn long;
the versorium, as it there moves into various
positions in the same circle, will always have re-
gard to the dimensions of that sphere and not
those of the terrella, as is seen in the diagram of
the effused magnetic forms. While some writers
posit as causes of the wonderful effects of the
loadstone occult and recondite virtues of things,
and others regard a property of the loadstone's
substance as the cause, we have discovered the
primary substantial form not in some more or
less probable foreshadowing of truth or in rea-
sons that admit of controversy; but as in many
other demonstrations, so in this most indisputa-
ble diagram of the forces magnetical effused by
the form, we grasp the true efficient cause. And
this (the form), though it is subject to none of
our senses and is therefore less perceptible to the
intellect, now appears manifest and visible be-
fore our very eyes through this formal act, which
proceeds from it as light proceeds from a source
of light. And here it is to be noted that a mag-
netic needle moved over the earth, or over a
terrella, or over the effused spheres, rotates com-
pletely twice in one circuit of its centre, like an
epicycle round its circle.
CHAPTER 12. The magnetic force is animate, or
imitates a soul; in many respects it surpasses the hu-
man soul while that is united to an organic body
WONDERFUL is the loadstone shown in many ex-
periments to be, and, as it were, animate. And
this one eminent property is the same which the
ancients held to be a soul in the heavens, in the
globes, and in the stars, in sun and moon. For
they deemed that not without a divine and ani-
mate nature could movements so diverse be pro-
duced, such vast bodies revolve in fixed times,
or potencies so wonderful be infused into other
bodies; whereby the whole world blooms with
most beautiful diversity through this primary
form of the globes themselves. The ancient phi-
losophers, as Thales, Heraclitus, Anaxagoras
Archelaus, Pythagoras, Empedocles, Parmeni-
des, Plato and all the Platonists — nor Greek
philosophers alone, but also the Egyptian and
Chaldean — all seek in the world a certain uni-
versal soul, and declare the whole world to be
endowed with a soul. Aristotle held that not the
universe is animate, but the heavens only; his
elements he made out to be inanimate; but the
stars were for him animate. As for us, we find
this soul only in the globes and in their homo-
genie parts, and albeit this soul is not in all globes
the same (for that in the sun or in certain stars
is much superior to that in other less noble
globes). Still in very many globes the souls agree
in their powers. Thus, each homogenic part tends
to its own globe and inclines in the direction
common to the whole world, and in all globes
the effused forms reach out and are projected in
a sphere all round, and have their own bounds —
hence the order and regularity of all the mo-
tions and revolutions of the planets, and their
circuits, not pathless, but fixed and determinate,
wherefore Aristotle concedes to the spheres and
heavenly orbs (which he imagines) a soul, for
the reason that they are capable of circular mo-
tion and action and that they move in fixed,
definite, tracks. And 1 wonder much why the
globe of earth with its effluences should have
been by him and his followers condemned and
driven into exile and cast out of all the fair order
of the glorious universe, as being brute and soul-
less. In comparison with the whole creation 'tis
a mere mite, and amid the mighty host of many
thousands is lowly, of small account, and de-
formate. And to it the Aristotelians add allied
elements that by like ill-fortune are also beggar-
ly and despicable. Thus Aristotle's world would
seem to be a monstrous creation, in which all
things are perfect, vigorous, animate, while the
earth alone, luckless small fraction, is imperfect,
dead, inanimate, and subject to decay. On the
other hand, Hermes, Zoroaster, Orpheus, rec-
ognize a universal soul. As for us, we deem the
whole world animate, and all globes, all stars,
and this glorious earth, too, we hold to be from
the beginning by their own destinate souls gov-
erned and from them also to have the impulse
of self-preservation. Nor are the organs required
for organic action lacking, whether implanted
in the homogenic nature or scattered through
the homogenic body, albeit these organs are not
made up of viscera as animal organs are, nor
consist of definite members; indeed in some
plants and shrubs the organs are hardly recog-
nizable, nor are visible organs essential for life
in all cases. Neither in any of the stars, nor in
ON THE LOADSTONE
105
the sun, nor in the planets that are most operant
in the world, can organs be distinguished or im-
agined by us; nevertheless, they live and endow
with life small bodies at the earth's elevated
points. If there is aught of which man may boast,
that of a surety is soul, is mind; and the other
animals, too, are ennobled by soul; even God,
by whose rod all things are governed, is soul.
But who shall assign organs to the divine intel-
lects, seeing that they are superior to all organ-
structure, nor are comprised in material organs ?
But in the bodies of the several stars the inborn
energy works in ways other than in that divine
essence which presides over nature; and in the
stars, the sources of all things, in other ways
than in animals; finally, in animals in other ways
than in plants. Pitiable is the state of the stars,
abject the lot of earth, if this high dignity of
soul is denied them, while it is granted to the
worm, the ant, the roach, to plants and morels;
for in that case worms, roaches, moths, were
more beauteous objects in nature and more per-
fect, inasmuch as nothing is excellent, nor pre-
cious, nor eminent, that hath not soul. But since
living bodies spring from earth and sun and by
them are animate, and since in the earth herb-
age springs up without sowing of seeds (e.g.,
when soil is taken out of the bowels of the earth
and carried to some great elevation or to the top
of a lofty tower and there exposed to the sun-
shine, after a little while a miscellaneous herb-
age springs up m it unbidden), it is not likely
that they (sun and earth) can do that which is
not in themselves; but they awaken souls, and
consequently are themselves possessed of souls.
Therefore the bodies of the globes, as being the
foremost parts of the universe, to the end they
might be in themselves and in their state en-
dure, had need of souls to be conjoined to them,
for else there were neither life, nor prime act,
nor movement, nor unition, nor order, nor co-
herence, nor conactus, nor sympathia, nor any
generation, nor alternation of seasons, and no
propagation; but all were in confusion and the
entire world lapse into chaos, and, in fine, the
earth were void and dead and without any use.
But only on the superficies of the globes is plain-
ly seen the host of souls and of animate exist-
ences, and in their great and delightful diversity
the Creator taketh pleasure. But the souls (in
the interior of the globes) confined, as it were,
by prison bars send not forth their effused im-
material forms beyond the limits of the body,
nor are bodies put in motion by them without
labour and exertion; a breath carries and bears
them forth; but if that breath be fouled or stilled
by mischance, the bodies lie like the world's rec-
rement or as the waste matter of the globes. But
the globes themselves remain and endure, ro-
tate and move in orbits, and without wasting
or weariness run their courses. The human soul
uses reason, sees many things, investigates many
more; but, however well equipped, it gets light
and the beginnings of knowledge from the outer
senses, as from beyond a barrier— hence the very
many ignorances and foolishnesses whereby our
judgments and our life-actions are confused, so
that few or none do rightly and duly order their
acts. But the earth's magnetic force and the
formate soul or animate form of the globes, that
are without senses, but without error and with-
out the injuries of ills and diseases, exert an un-
ending action, quick, definite, constant, direc-
tive, motive, imperant, harmonious, through the
whole mass of matter; thereby are the genera-
tion and the ultimate decay of all things on the
superficies propagated. For if it were not for the
movement whereby the daily revolution is ac-
complished, all things here on earth were wild
and disordered, and worse than desert and un-
used would they ever remain. Yet these move-
ments in nature's founts are not produced by
thoughts or reasonings or conjectures, like hu-
man acts, which are contingent, imperfect, and
indeterminate, but connate in them are reason,
knowledge, science, judgment, whence proceed
acts positive and definite from the very founda-
tions and beginnings of the world: these, be-
cause of the weakness of our soul, we cannot
comprehend. Wherefore, not without reason,
Thales, as Aristotle reports in his book On the
Soul, declares the loadstone to be animate, a
part of the animate mother earth and her be-
loved offspring.
BOOK SIXTH
CHAPTER 1. Of the globe of earth as a loadstone
HITHERTO we have spoken of the loadstone and
magnetic bodies, how they conspire together
and act on each other, and how they conform
themselves to the terrella and to the earth. Now
we have to treat of the globe of earth itself sep-
arately. All the experiments that are made on
the terrella, to show how magnetic bodies con-
form themselves to it, may — at least the prin-
cipal and most striking of them — be shown on
the body of the earth; to the earth, too, all mag-
netized bodies are associate. And first, on the
terrella the equinoctial circle, the meridians,
parallels, the axis, the poles, are natural limits:
similarly on the earth these exist as natural and
not merely mathematical limits. As on the pe-
riphery of a terrella a loadstone or the magnetic
needle takes direction to the pole, so on the
earth there are revolutions special, manifest,
and constant, from both sides of the equator:
iron is endowed with verticity by being
stretched toward the pole of the earth as to-
ward the pole of a terrella; again, by being laid
down and suffered to grow cool lying toward
the earth's pole, after its prior verticity has been
destroyed by fire, it acquires new verticity con-
formed to the position earthward. And iron rods
that have for a long time lain in the poleward
direction acquire verticity simply by regard-
ing the earth; just as the same rods, if they be
pointed toward the pole of a loadstone, though
not touching it, receive polar force. There is no
magnetic body that draws nigh in any way to
a loadstone which does not in like manner obey
the earth. As a loadstone is more powerful at
one end and at one side of the equator, so the
same thing is shown with a small terrella on a
large one. According to the difference in amount
and mode of friction in magnetizing a piece of
iron at a terrella, it will be powerful or weak in
performing its functions. In movements toward
the body of the earth, just as on a terrella, vari-
ation is produced by unlikeness and inequality
of prominences and by imperfections of the sur-
face; and all variation of the versorium or the
mariner's compass all over the earth and every-
where at sea— a thing that has so bewildered
men's minds— is found and recognized through
the same causes. The dip of the magnetic needle
(that wonderful turning of magnetic bodies to
the body of the terrella by formal progression)
is seen also in the earth most clearly. And that
one experiment reveals plainly the grand mag-
netic nature of the earth, innate in all the parts
thereof and diffused throughout. The magnetic
energy, therefore, exists in the earth just as in
the terrella, which is a part of the earth and
homogenic in nature with it, but by art made
spherical so it might correspond to the spheri-
cal body of the earth and be in agreement with
the earth's globe for the capital experiments.
CHAPTER 2. The magnetic axis of the earth remains
invariable
THE earth's magnetic axis, just as it passed
through the midearth in the very beginnings of
the moving world, so to-day tends through the
centre to the same points of the superficies, the
equinoctial line and plane also persisting the
same. For not, save with a vast demolition of
the terrestrial mass, may these natural bounds
be altered, as is easily shown by magnetic dem-
onstrations. Wherefore the opinion held by
Dominicus Maria of Ferrara, a man of rare abil-
ity, and who was the preceptor of Nicolaus
Copernicus, is to be rejected. It was based on
certain observations, and was as follows: "Some
years ago," he writes, "while considering Ptol-
emy's geography, I found the elevations of the
north pole given by him for the several regions
to fall short by one degree and ten minutes of
what they are in our time, which difference can
by no means be referred to an error of the table,
for it is not credible that the whole book should
be throughout equally wrong in the figures con-
tained in the tables; therefore we must suppose
the north pole brought toward the vertical
point. Thus a protracted observation began to
disclose to us things hid from our ancestors —
not through any sloth on their part, but be-
cause they lacked observation of a long period
by their predecessors. For very few places be-
fore Ptolemy's time were observed in elevations
106
ON THE LOADSTONE
107
of the pole, as he himself testifies in the begin-
ning of his Cosmographia: 'Hipparchus alone/
he writes, 'hath handed down to us the lati-
tudes of a few places; but many latitudes of dis-
tances, especially of distances to east and west,
have been fixed on a basis of general tradition,
and this is not from any indolence of writers,
but because they were unacquaint with a more
accurate mathematic.' Hence it is no wonder if
our predecessors have not noted the very slow
movement, seeing that in 1700 years it has ad-
vanced about one degree toward the uttermost
point of human habitation. This is shown at the
Straits of Gibraltar, where in Ptolemy's day
the north pole was raised 36^ degrees above
the horizon, while now it is 372/5 degrees. A like
difference is shown by Leucopetra (Capo dell'
Armi) in Calabria and sundry other places in
Italy, namely, places that have not changed
from Ptolemy's time to ours. Thus, in conse-
quence of this movement, places that now are
inhabited will one day be deserted, while those
that now are scorched by the tropic sun will,
albeit after a long time, be reduced to our tem-
perature. For this very slow movement will be
completed in 395,000 years."
Thus, according to Dominicus Maria's obser-
vations, the north pole is raised higher and the
latitudes of places are greater now than in the
past: from this he infers a change of latitudes.
But Stadius, holding the directly opposite opin-
ion, proves by observations that the latitudes
have grown less. "The latitude of Rome," says
he, "is given in the Geographica of Ptolemy as
41^3 degrees; and lest any one should say that
some error has crept into the text of Ptolemy,
Pliny relates, and Vitruvius in his Ninth Book
testifies, that at Rome on the day of the equinox
the ninth part of the gnomon's shadow is lack-
ing. But recent observation (as Erasmus Rhein-
hold states) gives the latitude of Rome in our
age as ^Vo degrees; so that you are in doubt
whether one half of a degree has been lost in
the centre of the world, or whether it is the re-
sult of an obliquation of the earth." From this
we may see how, on the basis of inexact obser-
vations, men conceive new and contrary opin-
ions as to the earth's mechanism, and postulate
absurd motions. For, as Ptolemy simply took
from Hipparchus a few latitudes and did not
himself observe them in many places, it is likely
that, knowing the position of the countries, he
made a conjectural estimate of the latitude of
cities, and set such conjectures down in his tables.
So, here, in Britain, the latitudes of cities vary
two or three degrees, as we know by experience.
Hence no new movement is to be postulated on
the ground of these miscalculations, nor is the
grand magnetic nature of the earth to be de-
formed for the sake of a judgment so rashly ar-
rived at. And these errors have crept into ge-
ography all the more easily because the mag-
netic force was quite unknown to authors. Be-
sides, observations of latitudes cannot be made
with exactitude save by experts, with the help
of large instruments, and by taking account of
refraction of lights.
CHAPTER 3. Of the daily magnetic revolution of the
globes, as against the time-honored opinion of a
primum mobile: a probable hypothesis
AMONG the ancients, Herachdes of Pontus, and
Ecphantus, the Pythagoreans Nicetas of Syra-
cuse and Aristarchus of Samos, and, as it seems,
many others, held that the earth moves, that
the stars set through the interposition of the
earth, and that they rise through the earth's
giving way: they do give the earth motion, and
the earth being, like a wheel, supported on its
axis, rotates upon it from west to east. The
Pythagorean Philolaus would have the earth to
be one of the stars, and to turn in an oblique
circle toward the fire, just as the sun and moon
have their paths: Philolaus was an illustrious
mathematician and a very experienced investi-
gator of nature. But when philosophy had come
to be handled by many, and had been given out
to the public, then theories adapted to the ca-
pacity of the vulgar herd or supported with
sophistical subtleties found entrance into the
minds of the many, and, like a torrent, swept
all before them, having gained favor with the
multitude. Then were many fine discoveries of
the ancients rejected and discredited —at the
least were no longer studied and developed.
First, therefore, Copernicus among moderns (a
man most worthy of the praise of scholarship)
undertook, with new hypotheses, to illustrate
the phenomena of bodies in motion; and these
demonstrations of reasons, other authors, men
most conservent with all manner of learning,
either follow, or, the more surely to discover
the alleged "symphony" of motion, do observe.
Thus the suppositions and purely imaginary
spheres postulated by Ptolemy and others for
finding the times and periods of movements,
are not of necessity to be accepted in the physi-
cal lectures of philosophers.
It is then an ancient opinion, handed down
from the olden time, but now developed by
great thinkers, that the whole earth makes a
diurnal rotation in the space of twenty-four
io8
WILLIAM GILBERT
hours. But since we see the sun, the moon, and
the other planets, and the whole heavenly host,
within the term of one day come and depart,
then either the earth whirls in daily motion
from west to east, or the whole heavens and all
the rest of the universe of things necessarily
speeds about from east to west. But in the first
place, it is not probable that the highest heaven
and all those visible splendors of the fixed stars
are swept round in this rapid headlong career.
Besides, what genius ever has found in one same
(Ptolemaic) sphere those stars which we call
fixed, or ever has given rational proof that 'there
are any such adamantine spheres at all ? No man
hath shown this ever; nor is there any doubt
that even as the planets are at various distances
from earth, so, too, are those mighty and mul-
titudinous luminaries ranged at various heights
and at distances most remote from earth: they
are not set in any sphaeric framework or firma-
ment (as is supposed), nor in any vaulted struc-
ture. As for the intervals (between the spheres)
imagined by some authors, they are matters of
speculation, not of fact; those other intervals
do far surpass them and are far more remote;
and, situated as they are in the heavens, at vari-
ous distances, in thinnest aether, or in that most
subtile fifth essence, or in vacuity — how shall
the stars keep their places in the mighty swirl
of these enormous spheres composed of a sub-
stance of which no one knows aught ? Astrono-
mers have observed 1022 stars; besides these,
innumerable other stars appear minute to our
senses; as regards still others, our sight grows
dim, and they are hardly discernible save by the
keenest eye; nor is there any man possessing
the best power of vision that will not, while the
moon is below the horizon and the atmosphere
is clear, feel that there are many more indeter-
minable and vacillating by reason of their faint
light, obscured because of the distance. Hence,
that these are many and that they never can
be taken in by the eye, we may well believe.
What, then, is the inconceivably great space
between us and these remotest fixed stars ? and
what is the vast immeasurable amplitude and
height of the imaginary sphere in which they
are supposed to be set ? How far away from earth
are those remotest of the stars: they are beyond
the reach of eye, or man's devices, or man's
thought. What an absurdity is this motion (of
spheres).
It is evident, therefore, that all the heavenly
bodies, being, as it were, set down in their des-
tined places, in them are conglobed whatever
elements bear to their own centres, and around
them are assembled all their parts. But if they
have a motion, it will be motion of each round
its proper centre, like the earth's rotation; or it
will be by a progression in an orbit, like that of
the moon; in so multitudinous a scattered flock
there will be no circular motion. And of the
stars, those situate nigh the equator would seem
to be borne around with greatest rapidity, while
others nigher the pole have a rather less rapid
movement; and others still, as though motion-
less, have but a small revolution. Yet no differ-
ences in the light, the mass, or the colors of the
light are perceptible for us; for they are as bril-
liant, as clear, as resplendent, or as faint (som-
bre, fuscai) toward the poles as nigh the equator
and the zodiac; and in their seats do they re-
main and there are they placed, nor are they
suspended from aught, nor fastened nor secured
in any vault. Far more extravagant yet is the
idea of the whirling of the supposititious prim-
um mobile, which is still higher, deeper, more
immeasurable; and yet this incomprehensible
primum mobile would have to be of matter, of
enormous altitude, and far surpassing all the
creation below in mass, for else it could not
make the whole universe down to the earth re-
volve from east to west, and we should have to
accept a universal force, an unending despot-
ism, in the governance of the stars, and a hate-
ful tyranny. This primum mobile presents no
visible body, is in no wise recognizable; it is a
fiction believed in by some philosophers, and
accepted by weaklings who wonder more at
this terrestrial mass here than at those distant
mighty bodies that baffle our comprehension.
But there cannot be diurnal motion of infin-
ity or of an infinite body, nor, therefore, of this
immeasurable primum mobile. The moon, neigh-
bor of earth, makes her circuit in twenty-seven
days; Mercury and Venus have a tardy move-
ment; Mars completes his period in two years,
Jupiter in twelve, Saturn in thirty. And the
astronomers who ascribe motion to the fixed
stars hold that it is completed, according to
Ptolemy, in 36,000 years, or, according to Co-
pernicus' observations, in 25,816 years; thus in
larger circles the motion and the completion of
the course are evermore slow; and yet this prim-
um mobile, surpassing all else in height and
depth, immeasurable, has a diurnal revolution.
Surely that is superstition, a philosophic fable,
now believed only by simpletons and the un-
learned; it is beneath derision; and yet in times
past it was supported by calculation and com-
parison of movements, and was generally ac-
cepted by mathematicians, while the importu-
ON THE LOADSTONE
109
natc rabble of philophastcrs egged them on.
The motions of the heavenly bodies (i.e., of
the planets) seem all to be eastward, and ac-
cording to the succession of the zodiacal signs;
and mathematicians and philosophers of the
vulgar sort do also believe that the fixed stars
progress in the same way with a very slow move-
ment: to these stars they must needs, through
their ignorance of the truth, add a ninth sphere.
But now this inadmissible primum mobile, this
fiction, this something not comprehensible by
any reasoning and evidenced by no visible star,
but purely a product of imagination and math-
ematical hypothesis, accepted and believed by
philosophers, and reared into the heavens and
far beyond all the stars, this must needs by a
contrary incitation wheel from east to west,
counter to the tendence of all the rest of the
universe.
Whatever in nature moves naturally, the
same is impelled by its own forces and by a con-
sentient compact of other bodies. Such is the
motion of the parts to a whole, of the globes and
stars throughout the universe with each other
accordant; such is the circular propulsion of the
planets* bodies, each the other's career observ-
ing and inciting. But as regards this primum
mobile with its contrary and most rapid career,
where are the bodies that incite it, that propel
it ? Where is the nature conspiring with it ? and
what mad force lies beyond the primum mobile?
— for the agent force abides in bodies them-
selves, not in space, not in the interspaces.
But he who supposes that all these bodies are
idle and inactive, and that all the force of the
universe pertains to those spheres, is as foolish
as the one who, entering a man's residence,
thinks it is the ceilings and the floors that govern
the household, and not the thoughtful and prov-
ident good-man of the house. So, then, not
by the firmament are they borne, not from the
firmament have they movement or position;
and far less are those multitudes of stars whirled
round en masse by the primum mobile, and taken
up at random and swept along in a reversed di-
rection at highest velocity.
Ptolemy of Alexandria, it seems to me, was
over- timid and scrupulous in apprehending a
break-up of this nether world were earth to
move in a circle. Why does he not apprehend
universal ruin, dissolution, confusion, conflagra-
tion, and stupendous celestial and supercelestial
calamities from a motion that surpasses all imag-
ination, all dreams and fables and poetic li-
censes— a motion ineffable and inconceivable ?
So, then, we are borne round and round by the
earth's daily rotation—a more congruous sort
of motion; and as a boat glides over the water,
so are we whirled round with the earth, the
while we think we stand still and are at rest.
This seems to some philosophers wonderful and
incredible, because of the ingrained belief that
the mighty mass of the earth makes an orbital
movement in twenty-four hours: it were more
incredible that the moon should in the space of
twenty-four hours traverse her orbit or com-
plete her course; more incredible that the sun
and Mars should do so; still more that Jupiter
and Saturn; more than wonderful would be the
velocity of the fixed stars and firmament; and
let them imagine as best they may the wonders
that confront them in the ninth sphere. But
it is absurd to imagine a primum mobile, and,
when imagined, to give to it a motion that is
completed in twenty-four hours, denying that
motion to the earth within the same space of
time. For a great circle of earth, as compared to
the circuit of the primum mobile is less than a
stadium1 as compared to the whole earth. And
if the rotation of the earth seems headlong and
not to be permitted by nature because of its ra-
pidity, then worse than insane, both as regards
itself and the whole universe, is the motion of
the primum mobile, as being in harmony or pro-
portion with no other motion. Ptolemy and the
Peripatetics think that all nature must be
thrown into confusion, and the whole structure
and configuration of this our globe destroyed by
the earth's so rapid rotation. The diameter of
the earth is 1718 German miles; the greatest
elongation of the new moon is 65, the least 55,
semi-diameters of the earth; but probably its
orbit is still larger. The sun at his greatest ec-
centricity is distant 1142 semi-diameters from
earth; Mars, Jupiter, Saturn, as they are slow
in movement, so are far more distant from the
earth. The best mathematicians regard the dis-
tances of the firmament and the fixed stars as
indeterminable; to say nothing of the ninth
sphere, if the convexity of the primum mobile be
fairly estimated in its proportion to the rest, it
must travel over as much space in one hour as
might be comprised within three thousand
great circles of the earth, for on the convexity
of the firmament it would travel over more than
eighteen hundred such circles: but what struc-
ture of iron can be imagined so strong, so tough,
that it would not be wrecked and shattered to
pieces by such mad and unimaginable velocity ?
1 Ancient measure of length, equal to 600 Greek or 625
Roman feet, or 125 Roman paces, or to 606 feet 9 inches
English.
no
The Chaldees believed the heavens to be light.
But in light there is no such firmness, neither in
the fire-firmament of Plotinus, nor in the fluid
or watery heavens of God-inspired Moses, nor
in the supremely tenuous and transparent firm-
ament that stands between our eye and the
lights of the stars, but does not intercept the
same. Hence we must reject the deep-seated
error about this mad, furious velocity, and this
forceful retardation of the rest of the heavens.
Let the theologues reject and erase these old
wives' stories of a so rapid revolution of the
heavens which they have borrowed from certain
shallow philosophers. The sun is not swept
round by Mars' sphere (if sphere he have) and
its motion, nor Mars by Jupiter's sphere, nor
Jupiter by Saturn's: the sphere of the fixed stars
too, seems moderate enough, save that move-
ments are attributed to the heavens that really
are earth movements, and these produce a cer-
tain change in the phenomena. The higher do
not tyrannize over the lower, for the heaven
both of the philosopher and of the divine must
be gentle, happy, tranquil, and not subject to
changes; neither will the violence, fury, velo-
city, and rapidity of the primum mobile bear
sway. That fury descends through all the ce-
lestial spheres and heavenly bodies, enters the
elements of the philosophers, sweeps the fire
along, whirls the air around, or at least the
greater part thereof; leads in its train the uni-
versal ether, and causes it to whirl round as
though it were a solid and firm body, whereas
it is a most tenuous substance, that neither of-
fers resistance nor is ductile; and leads captive
the fires of the upper heavens. O wondrous
steadfastness of the globe of earth, that alone is
unconquered' And yet the earth is holden nor
stayed in its place by any chains, by no heavi-
ness of its own, by no contiguity of a denser or
a more stable body, by no weights. The sub-
stance of the terrestrial globe withstands and
resists universal nature.
Aristotle imagines a philosophy of motions
simple or complex, holds that the heavens move
with a simple circular motion, and his elements
with motion in a right line; that the parts of the
earth tend to the earth in right lines; that they
impinge upon it at the superficies at right angles
and seek its centre, and there always rest; and
that hence the whole earth stands in its place,
held together and compacted by its own weight.
This coherence of parts and this consolidation of
matter exists in the sun, the moon, the planets,
the fixed stars— in short, in all those spherical
bodies whose parts cohere and seek their sev-
WILLIAM GILBERT
eral centres; else would the heavens rush to de-
struction and their grand order disappear. But
these heavenly bodies have a circular motion,
and hence the earth, too, may have its motion,
for this motion is not, as some suppose, adverse
to cohesion nor to production. For, inasmuch
as this motion is intrinsic in the earth and natu-
ral, and as there is nothing without that may
convulse it or with contrary motions impede it,
it revolves untroubled by any ill or peril; it
moves on under no external compulsion; there
is nought to make resistance, nothing to give
way before it, but the path is open. For since it
revolves in a space void of bodies, the incorpore-
al aether, all atmosphere, all emanations of land
and water, all clouds and suspended meteors,
rotate with the globe: the space above the
earth's exhalations is a vacuum; in passing
through vacuum even the lightest bodies and
those of least coherence are neither hindered
nor broken up. Hence the entire terrestrial
globe, with all its appurtenances, revolves pla-
cidly and meets no resistance. Causelessly,
therefore, and superstitiously, do certain faint-
hearts apprehend collisions, in the spirit of Lu-
cius Lactantius, who, like the most unlearned
of the vulgar, or like an uncultured bumpkin,
treats with ridicule the mention of antipodes
and of a round globe of earth.
From these arguments, therefore, we infer,
not with mere probability, but with certainty,
the diurnal rotations of the earth; for nature
ever acts with fewer rather than with many
means; and because it is more accordant to rea-
son that the one small body, the earth, should
make a daily revolution than that the whole
universe should be whirled around it. I pass by
the earth's other movements, for here we treat
only of the diurnal rotation, whereby it turns to
the sun and produces the natural day (of twenty-
four hours) which we call nycthemeron. And, in-
deed, nature would seem to have given a motion
quite in harmony with the shape of the earth,
for the earth being a globe, it is far easier and
far more fitting that it should revolve on its
natural poles, than that the whole universe,
whose bounds we know not nor can know,
should be whirled round; easier and more fit-
ting than that there should be fashioned a
sphere of the primum mobile— a thing not re-
ceived by the ancients, and which even Aris-
totle never thought of or admitted as existing
beyond the sphere of the fixed stars; finally,
which the holy Scriptures do not recognize, as
neither do they recognize a revolution of the
whole firmament.
ON THE LOADSTONE
CHAPTER 4. That the earth hath a circular motion
AND now, though philosophers of the vulgar sort
imagine, with an absurdity unspeakable, that
the whole heavens and the world's vast magni-
tude are in rotation, it remains that the earth
daily makes one revolution; for in no third mode
can the apparent revolutions be accounted for.
The day, therefore, which we call the natural
day is the revolution of a meridian of the earth
from sun to sun. And it makes a complete revo-
lution from a fixed star to the same fixed star
again. Bodies that by nature move with a mo-
tion circular, equable, and constant, have in their
different parts various metes and bounds. Now
the earth is not a chaos nor a chance medley
mass, but through its astral property has limits
agreeable to the circular motion, to wit, poles
that are not merely mathematical expressions,
an equator that is not a mere fiction, meridians,
too, and parallels; and all these we find in the
earth, permanent, fixed, and natural; they are
demonstrated with many experiments in the
magnetic philosophy. For in the earth are poles
set at fixed points, and at these poles the vertic-
ity from both sides of the plane of the equator
is manifested with greatest force through the
co-operation of the whole; and with these poles
the diurnal rotation coincides. But no revolu-
tions of bodies, no movements of planets, show
any sensible, natural poles in the firmament or
in any pnmum mobile; neither does any argu-
ment prove their existence; they are the prod-
uct of imagination. We, therefore, having di-
rected our inquiry toward a cause that is mani-
fest, sensible, and comprehended by all men, do
know that the earth rotates on its own poles,
proved by many magnetical demonstrations to
exist. For not in virtue only of its stability and
its fixed permanent position does the earth pos-
sess poles and verticity; it might have had an-
other direction, as eastward or westward, or to-
ward any other quarter. By the wonderful wis-
dom of the Creator, therefore, forces were im-
planted in the earth, forces primarily animate,
to the end the globe might, with steadfastness,
take direction, and that the poles might be op- E
posite, so that on them, as at the extremities of
an axis, the movement of diurnal rotation might
be performed. Now the steadfastness of the poles
is controlled by the primary soul. Thus it is for
the good of the earth that the collimations of
the verticities do not continually regard a fixed
point in the firmament and in the visible heav-
ens. For the changes of the equinoxes are caused
by a certain inflection of the earth's axis, yet in
in
this inflection the earth hath from her own forces
a steadfastness in her motion. In her rotation the
earth bears on her own poles; for since the ver-
ticity is fixed in A and #, and the axis horizon-
tal, at C and D (equinoctial line) the parts are
free, all the forces being diffused on both sides
from the plane of the equator toward the poles
in the aether, which is without resistance, or in
vacuum; and, A and B remaining constant, C
revolves toward D both by natural conformity
and fitness, as also for the sake of a necessary
good and avoidance of ill, but most of all because
the effused spheres of solar influence and of solar
light do impel. And it revolves not in a new
track or one assigned from without, but, in the
general trend of all the rest of the planets, tends
from west to east. For all planets have a like
movement to the east, in accordance with the
succession of the zodiacal signs, whether it be
Mercury or Venus within the sun's orbit, or
whether they revolve round the sun. That the
112
earth is fitted for circular movement is proved
by its parts, which, when separated from the
whole, do not simply travel in a right line, as
the Peripatetics taught, but rotate also. A load-
stone placed in a wooden vessel is put in water
so that it may float freely, rotate, and move
about. If the pole B of the loadstone be made to
point, unnaturally, toward the south F, the ter-
rella revolves round its centre in a circular mo-
tion on the plane of the horizon toward the
north £", where it comes to a rest, and not at C
or at D. So acts a small stone weighing only four
ounces; and a powerful loadstone of 100 pounds
will make the same movement as quickly; and
the largest mountain of loadstone would revolve
in the same way were it to be set afloat on a wide
stream or in the deep sea; and yet a magnetic
body is far more hindered by water than is the
whole earth by the air. The whole earth would
act in the same way, were the north pole turned
aside from its true direction; for that pole would
go back, in the circular motion of the whole,
toward Cynosura.
Yet this motion is nothing by that circular
motion wherewith the parts naturally tend to
their own places. The whole earth regards Cyn-
osura by its steadfast nature; and similarly each
true part of the earth seeks a like place in the
world, and turns with circular motion to that
position. The natural movements of the whole
and of the parts are alike: hence, since the parts
move in a circle, the whole, too, hath the power
of circular motion. A spherical loadstone, when
floated in water, moves circularly on its centre
to become (as it seems) conformed to the earth
on the plane of the equator. Thus, too, would it
move on any other great circle if it were free to
move, so that in the dip compass there is circu-
lar movement on the meridian (if there be no
variation), or, if there is variation, on a great
circle drawn from the zenith through the varia-
tion point in the horizon. And this circular move-
ment of the loadstone to its true and natural
position shows that the whole earth is fitted,
and by its own forces adapted for a diurnal cir-
cular motion. I omit what Petrus Peregrinus so
stoutly affirms, that a terrella poised on its poles
in the meridian moves circularly with a com-
plete revolution in twenty-four hours. We have
never chanced to see this: nay, we doubt if there
is such movement, both because of the weight
of the stone itself, and also because the whole
earth, as it moves of itself, so is propelled by the
other stars; but this does not occur proportion-
ately in any part of the earth, a terrella for ex-
ample. The earth moves by its primary form
WILLIAM GILBERT
and natural desire, for the conservation, per-
fecting, and beautifying of its parts, toward the
more excellent things: this is more probable than
that those fixed luminous orbs, and the planets
and the sun, foremost of all and divine, while
they get no aid of any sort from earth, no re-
freshment, no force whatever, should vainly cir-
cle round it, and that the whole host of heaven
should make everlasting rounds about the earth,
without any profit whatever to those stars
themselves.
The earth therefore rotates, and by a certain
law of necessity, and by an energy that is innate,
manifest, conspicuous, revolves in a circle to-
ward the sun; through this motion it shares in
the solar energies and influences; and its vertic-
ity holds it in this motion lest it stray into every
region of the sky. The sun (chief inciter of ac-
tion in nature), as he causes the planets to ad-
vance in their courses, so, too, doth bring about
this revolution of the globe by sending forth the
energies of his spheres—his light being effused.
And were not the earth to revolve with diur-
nal rotation, the sun would ever hang with its
constant light over a given part, and, by long
tarrying there, would scorch the earth, reduce
it to powder, and dissipate its substance, and the
uppermost surface of earth would receive griev-
ous hurt: nothing of good would spring from
earth, there would be no vegetation; it could not
give life to the animate creation, and man would
perish. In other parts all would be horror, and
all things frozen stiff with intense cold: hence
all its eminences would be hard, barren, inac-
cessible, sunk in everlasting shadow and unend-
ing night. And as the earth herself cannot en-
dure so pitiable and so horrid a state of things
ON THE LOADSTONE
on either side, with her astral magnetic mind
she moves in a circle, to the end there may be,
by unceasing change of light, a perpetual vicis-
situde, heat and cold, rise and decline, day and
night, morn and even, noonday and deep night.
So the earth seeks and seeks the sun again, turns
from him, follows him, by her wondrous mag-
netical energy.
And not only from the sun would ill impend,
were the earth to stand still and be deprived of
the benefit of his rays; from the moon also great
dangers would threaten. For we see how the
ocean swells and comes to flood under certain
positions of the moon. But if by the daily rota-
tion of the earth the moon did not quickly pass,
the sea would rise unduly at some parts and
many coasts would be overwhelmed by mighty
tides. Lest the earth, then, should in divers ways
perish and be destroyed, she rotates in virtue of
her magnetic and primary energy. And such are
the movements in the rest of the planets, the
motion and light of other bodies especially urg-
ing. For the moon also turns round during its
menstrual circuit that it may on all its parts suc-
cessively receive the sun's light, which it enjoys,
with which it is refreshed like the earth itself;
nor could the moon without grave ill and sure
destruction stand the unceasing incidence of the
light on one of its sides only.
Thus each of the moving globes has circular
motion, either in a great circular orbit or on its
own axis or in both ways. But that all the fixed
stars, and the planets, and all the higher heav-
ens, still revolve simply for the earth's sake is
for the mind of a philosopher a ridiculous sup-
position. The earth then revolves, and not the
whole heavens; and this movement brings growth
and decay, gives occasion for the generation of
animated things, and arouses the internal heat
to productiveness. Hence does matter vegetate
to receive forms, and from this primary revolu-
tion of the earth natural bodies have prime in-
citation and original act. The motion of the
whole earth, therefore, is primary, astral, circu-
lar about its poles, whose verticity rises on both
sides from the plane of the equator, and the en-
ergy is infused into the opposite ends, so that
the globe by a definite rotation might move to
the good, sun and stars inciting. But the simple
right-downward motion assumed by the Peri-
patetics is the movement of weight, of coacerva-
tion, of separated parts, in the ratio of their mat-
ter, by right lines toward the earth's centre,
these tending to the centre by the shortest route.
The motions of separate magnetical parts of the
earth are, besides that of coacervation, those of
coition, revolution, and direction of the parts to
the whole, into harmony and agreement of the
form.
CHAPTER 5. Arguments of those who deny the
earth's motion; and refutation thereof
IT will not be superfluous to weigh also the argu-
ments of those who deny that the earth moves,
to the end we may the better satisfy the herd of
philosophers who deem the steadfastness and im-
mobility of the globe to be proved by incontro-
vertible arguments. Aristotle does not allow that
the earth moves circularly, for, says he, then
every part thereof would take the same motion;
but inasmuch as all separated parts tend to the
middle point in right lines, that circular motion
were something imposed by force, were contrary
to nature, were not perpetual. But we have al-
ready proven that all true parts of the earth do
move circularly, and that all magnetic bodies
(when fitly arranged) are borne round in a cir-
cle. But they tend to the earth's centre in a right
line (if the way is open) by the motion of coacer-
vation, as to their origin; they move with vari-
ous motions to conformation of the whole; a
terrella moves circularly by its inborn forces.
"Besides," says Aristotle, "all things that move
in a circle seem afterward to lose the first move-
ment and to be carried on by several motions
other than the first. The earth, too, whether
situate in the middle or near the middle of the
world, must needs have two movements; and
were that the case there must needs be progres-
sions and retrogressions of the fixed stars: no
such thing is seen, however, but evermore the
same stars are rising and setting in the same
places." Yet it by no means follows that a two-
fold motion is attributed to the earth. And if
there be but the one diurnal motion of the earth
round its poles, every one sees that the stars
must always rise and set in the same way, at the
same points of the horizon, even though there
be another movement for which we are not con-
tending; because the changes in the smaller
sphere produce in the fixed stars no variation of
aspect on account of the great distance, unless
the earth's axis changes position: of this we
treat in the chapter treating of the cause of the
precession of the equinoxes.
In this reasoning (of Aristotle's) are many
flaws. For if the earth rotates, that, as we have
shown, must be due not to the action of the first
sphere, but to its own native forces. And if the
motion were produced by the first sphere, there
would be no alternations of days and nights, for
the globe would then make her revolution along
WILLIAM GILBERT
with the primum mobile. And it does not follow,
because the rest of the heavenly bodies move
with a twofold motion, that the earth has a two-
fold motion when it rotates round its centre.
Then, too, Aristotle does not clearly apprehend
the reason of the case, nor do his translators ei-
ther : roi)rov 8l0viJLpalvovTOSt bvayKdlov ylyvecr-
0ai 7rap66ous Kal rpoir as T&V kvbebtiJ,kvwv affrpvv
(On the Heavens, Ch. 14)— />., if that be so,
there must needs be mutations and regressions
of the fixed stars. Some translate rpowas "regres-
sions" or "retrogressions," others "diversions":
these terms can in no wise be understood of axial
motion unless Aristotle means that the earth is
whirled by the primum mobile round other poles
different even from those of the first sphere —
which is quite absurd.
More recent writers hold that the Eastern
Ocean must needs, in consequence of this mo-
tion, so be driven toward the regions to the west
that parts of the earth which are dry and water-
less would of necessity be daily submerged be-
neath the waters. But the ocean gets no impul-
sion from this motion, as there is no resistance,
and even the whole atmosphere is carried round
also; for this reason, in the rapid revolution of
the earth, things in the air around are not left
behind nor do they have the appearance of mov-
ing westward; the clouds stand motionless in the
atmosphere, save when impelled by the force of
the winds; and objects thrown up into the air
fall back again to their places. But they are dul-
lards who think that steeples, churches, and other
edifices must necessarily be shaken and topple
down if the earth moves: antipodes might fear
lest they should slip over to the other side of the
globe; navigators might dread lest in making
the circle of the whole globe they might, once
they had descended below the plane of our hori-
zon, drop down into the opposite part of the
sky. But these are old-wives' imaginings and
ravings of philosophasters who, when they un-
dertake to discourse of great things and the fab-
ric of the world and attempt aught, are unable
to understand hardly anything ultra crepidam.
The earth they hold to be the centre of a circle
and to stand motionless in the general revolu-
tion. But the stars or the planetary globes do
not move in a circle round the centre of the
earth; nor is the earth the centre — if it be in the
centre — but a body around the centre.
And it is inconsistent that the Peripatetics'
heavenly bodies should rest on so frail, so per-
ishable, a thing as the earth's centre.
Now generation results from motion, and
without motion all nature would be torpid. The
sun's motions, the moon's motions, produce
changes; the earth's motion awakens the inner
life of the globe; animals themselves live not
without motion and incessant working of the
heart and the arteries. As for the single motion
in a right line to the centre, that this is the only
movement in the earth, and that the movement
of an individual body is one and single, the argu-
ments for it have no weight, for that motion in
a right line is but the inclination toward their
origin, not only of the earth, but also of the
parts of the sun, the moon, and all the other
globes; but these move in a circle also. Joannes
Costeus, who is in doubt as to the cause of the
earth's motion, regards the magnetic energy to
be intrinsic, active, and controlling; the sun he
holds to be an extrinsic promovent cause; nor is
the earth so mean and vile a body as it is com-
monly reputed to be. Hence, according to him,
the diurnal motion is 'produced by the earth, for
the earth's sake and for the earth's behoof.
They (if such there be) who assert that this
movement of the earth takes place not only in
longitude but also in latitude, speak nonsense;
for nature has set in the earth definite poles and
has established definite and not confused revo-
lutions. Thus the moon turns round to the sun
in its monthly course, the while ever regarding
with definite poles definite parts of the heavens.
It were absurd to suppose that the atmosphere
moves the earth; for the air is but exhalation
and the effluvium of the earth given out in every
direction; winds, too, are only motions of the
exhalation here and there along the earth's sur-
face; the depth of the air current is trifling, and
there are in every region various winds from
different and opposite points. Some authors, not
finding the cause of the revolution in the earth's
matter— for there they say they find only solid-
ity and consistence— maintain that it is not to
be found in the form, and will admit as qualities
of the earth only cold and dryness, which can-
not produce the earth's motion. The Stoics at-
tribute to the earth a soul, and hence they de-
clare, amid the derision of the learned, that the
earth is an animal. This magnetical form, be it
energy or be it soul, is astral. Let the learned
lament and weep for that neither the early Peri-
patetics, nor the common run of philosophasters,
nor Joannes Costeus, who mocks at this sort of
thing, were capable of appreciating this grand
and most extraordinary fact of nature. As for
the objection that the superficial unevenness
produced by mountains and valleys would pre-
vent diurnal revolution, it is of no weight; for
mountains do not mar the rotundity of the earth
ON THE LOADSTONE
— as compared with the entire earth, mountains
are but trifling excrescences: besides, the earth
does not rotate without carrying along with it
its effluences. Beyond the effluences there is no
resistance. The earth's motion is performed with
as little labor as the motions of the other heav-
enly bodies: neither is it inferior in dignity to
some of these. To say that it is folly to suppose
the earth is more eager for the face of the sun
than the sun for the face of the earth, is mere
wilfulness and ignorance. Of the cause of the
rotation I have oft spoken. If any one were to
look for the cause of the rotation or any other
tendency of the earth on the globe-encircling
ocean, or in the movement of the atmosphere,
or in the heaviness of the earth's mass, he would
reason as stupidly as do those who obstinately
cling to an opinion because it was held by the
ancients. Ptolemy 's arguments are of no account:
for our true principles once laid down, the truth
is visible, and it is useless to refute Ptolemy. So
let Costeus and the philosophers recognize how
unprofitable and vain a thing it is to take their
stand on the doctrines and unproved theories of
certain ancient writers. Many persons cannot
see how it is (if the earth rotates) that a ball of
iron or lead dropped from a very high tower
falls exactly on the spot right below; or how
cannon-balls fired from a large culverin with
equal charges of gunpowder of the same quality,
and with the gun pointed at the same angle with
the horizon, have exactly the same range to east-
ward and to westward, the earth moving to the
east. But they who urge such arguments are mis-
taken through not understanding the nature of
primary globes and the combination of parts
with their globes, albeit not conjoined thereto
with bonds of solid matter. But the earth in its
diurnal revolution does not so move that its
more solid circumference is separated from the
bodies circumfused; on the contrary, all the cir-
cumfused effluences, and all heavy bodies there-
in, howsoever shot thereinto, advance simulta-
neously and uniformly with the earth because
of the general coherence. This is the case in all
primary bodies — the sun, moon, earth — the
parts betaking themselves to their origin and
founts, whereunto they are attached with the
same appetence with which what we call heavy
bodies are attached to earth. Thus lunar bodies
tend to the moon, solar to the sun, within the
respective spheres of their effluences. These ef-
fluences cohere through continuity of su bstance ;
and heavy bodies, too, are united to earth by
their heaviness and advance with it in the gen-
eral movement, especially when no resistance
of bodies hinders. And, for this reason, the di-
urnal revolution of the earth does not sweep
bodies along nor retard them: they neither out-
strip the earth's motion nor fall behind when
shot with force, whether to east or to west. Let
EFG be the earth, A the centre, LE the ascend-
ing effluences. As the sphere of the effluences
moves with the earth, so the part of the sphere
on the right line LE proceeds undisturbed in
the general rotation. In LE the heavy body M
falls perpendicularly to E, the shortest route
centreward; nor is this right motion of Ma com-
posite motion, i.e., resultant of a motion of co-
acervation and a circular motion, but simple
and direct, never going out of the line LE. And
an object shot with equal force from E toward
F, and from E toward G, has the same range in
both directions, though the diurnal rotation of
the earth goes on— even as twenty steps taken
by one man cover the same distance eastward
as westward. Hence the diurnal revolution of
the earth is not at all refuted by the illustrious
Tycho Brahe through such arguments as these.
The tendence to its centre (called by philos-
ophers, weight) works no resistance to the di-
urnal revolution, neither does it give direction
to the earth, nor keep in place the parts of the
earth, which have no weight when resting in the
earth's solid substance: there they have no long-
er any tendence, but are at rest in its mass. If
there be a flaw in the mass, a cavity of 1000 fath-
oms for example, a homogenic part of the earth
or compacted terrestrial matter descends
through that space, be it filled with water or
with air, to a more definite centre than air or
water, and seeks the solid globe. But the centre
of the earth, as also the whole earth itself, has no
weight: separated parts tend to their prindpium,
and this tendence we call weight: parts in union
WILLIAM GILBERT
arc at rest, and even if they had weight, they
would cause no impediment to the diurnal revo-
lution. For if around the axis AB a weight be at
C, it is balanced by E\ at F it is balanced by G;
CHAPTER 6,
tola,
if at //, by 7. And, similarly, if it is at L, it is
balanced by M. Thus the whole globe, having a
natural axis, is balanced in equilibrium and is set
in motion easily by the slightest cause, but chiefly
for the reason that the earth, in its own place, is
in no wise heavy nor needs any balancing. Hence
no weight hinders the diurnal revolution, and no
weight gives to the earth direction or continu-
ance in its place. It is therefore plain that no argu-
ment of sufficient force has yet been formed by
philosophers to refute the earth's motion.
. Of the cause of the definite time of the
\tal revolution of the earth
THE causes of the diurnal motion are to be found
in the magnetic energy and in the alliance of
bodies: that is to say, why a revolution of the
earth is performed in the term of 24 hours. For
no ingenious artifice, whether of clepsydra, or
of hour-glasses, or of time-pieces with toothed
wheels and driven by the tension of a steel plate,
can show any difference of time. But the diurnal
revolution once accomplished comes on again.
Now we will take a day to mean a complete rev-
olution of a meridian of the earth from sun to
sun. This is a little less than the total revolu-
tion; for in 365^ turnings of a meridian to the
sun a year is completed. Because of this fixed and
constant motion of the earth the number and
time of 365 days 5 hours 55 minutes are always
fixed and settled, barring that for other causes
there are certain trifling differences. Thus the
earth re vol ves, not fortuitously nor by chance,
nor with a headlong motion, but evenly, with a
certain high intelligence and with a wonderful
steadiness, even like the rest of the movable stars
which have fixed periods for their movements.
Thus, inasmuch as the sun itself is the mover
and inciter of the universe, the other planets
that are situate within the sphere of his forces,
being impelled and set in motion, do also with
their own forces determine their own courses
and revolve in their own periods, according to
the amplitude of their greater rotation and the
differences of the forces effused and the percep-
tion of a greater good. Hence it is that Saturn,
having a greater course to run, revolves in a
longer time, while Venus revolves in nine
months, and Mercury in 80 days, according to
Copernicus; and the moon makes the circuit of
the earth in 29 days, 12 hours, 44 minutes. We
have asserted that the earth turns on its centre,
making one day in its revolution sunward. The
moon goes round the earth in a monthly course,
and when after its prior conjunction with the
sun it comes to conjunction again, it constitutes
one month, or one lunar day. The mean distance
of the moon's orbit, according to the calcula-
tions of Copernicus and other later astronomers,
is distant from the earth's centre about 295/5 di-
ameters of the earth. A solar revolution of the
moon in her orbit takes 29 days 12 hours 44
minutes. We reckon her periodic time by her
return to the same position relatively to the sun,
making the moon's solar revolution, not by her
return to the same absolute position, making
the complete or stellar revolution, just as one
day on earth is reckoned as the planets return to
the same position relatively to the sun, and not
absolutely; because the sun is the cause of both
the earth's and the moon's motions. Also, be-
cause (as more recent astronomers suppose) the
month, as measured between solar conjunctions,
is really the full period of revolution, because of
the earth's motion in her great orbit. Diameters
bear a constant ratio to circumferences. And the
moon's orbit is a little more than twice
times the length of great circles on the earth.
Thus the moon and the earth agree in a two-
fold ratio of motion, and the earth rotates in its
diurnal motion in the space of 24 hours; because
the moon has a motion proportioned to the earth,
and the earth has a motion agreeing in a two-
fold proportion with the moon's motion. There
is some difference in minutes, for the distances
of the stars are not sufficiently determined in
minutes, nor are astronomers agreed thereupon.
So, then, the earth rotates in the space of 24
hours, even as the moon does in her monthly
course, by a magnetical compact of both, the
globes being impelled forward according to the
ratio of their orbits, as Aristotle admits (On the
Heavens, 11. 10). "It comes about," says he, "that
the motions of each are performed in a ratio, to
wit, in the same intervals whereby some are
ON THE LOADSTONE
117
quicker, others slower." But as between the
moon and the earth, it is more reasonable to be-
lieve that they are in agreement, because, being
neighbor bodies, they are very like in nature and
substance, and because the moon has a more
manifest effect on the earth than have any of
the other stars, except the sun; also the moon
alone of all planets directs its movements as a
whole toward the earth's centre, and is near of
kin to earth, and as it were held by ties to earth.
Such, then, is the symmetry and harmony of
the moon's and the earth's movements, very
different from the oft-mentioned harmony of
the celestial motions, which requires that the
nearer any sphere is to the primum mobile and
to the imaginary and fictitious rapid first mo-
tion, the less it opposes it and the more slowly it
is borne by its own motion from west to east;
but that the farther it is away the more rapidly
and the more freely it performs its motion, and
hence that the moon (being farthest from the
primum mobile) revolves with greatest rapidity.
These absurdities have been accepted for the
sake of the primum mobile, and so that it might
seem to have some effect in retarding the move-
ments of the nether heavens; as though the mo-
tion of the stars was due to retardation, and was
not inborn and natural to them, and as though
the rest of the heavens (the primum mobile alone
excepted) were ever driven by a mighty force
with a mad impulsion. Far more probable is it
that the stars revolve symmetrically, with a cer-
tain mutual concert and harmony.
CHAPTER 7. Of the earth's primary magnetic na-
ture, whereby her poles are made different from the
poles of the ecliptic
HAVING shown the nature and causes of the
earth's diurnal revolution, produced partly by
the energy of the magnetic property and partly
by the superiority of the sun and his light, we
have now to treat of the distance of the earth's
poles from those of the ecliptic — a condition
very necessary for man's welfare. For if the poles
of the world or the earth were fixed at the poles
of the zodiac, then the equator would lie exactly
under the line of the ecliptic, and there would
be no change of seasons — neither winter, nor
summer, nor spring, nor fall — but the face of
things would persist forever unchanging. Hence
(for the everlasting good of man) the earth's
axis declined from the pole of the zodiac just
enough to suffice for generation and diversifica-
tion. Thus the declination of the tropics and the
inclinations of the earth's pole always stand in
the 24th degree, but is at present only 23 deg.
28 min., or, according to others, 29 minutes;
but formerly the declination was 23 deg. 52
min., and that is the uttermost limit of declina-
tion so far observed. This has been wisely or-
dered by nature and settled by the earth's pri-
mary eminency. For were those poles — those of
the earth and the ecliptic — to be much farther
apart, then as the sun approached the tropic all
things would be waste and ruin, in any high lati-
tude of the other and neglected portion of the
globe, because of the protracted absence of the
sun. But now all things are so disposed that the
entire globe of earth has its own changes in due
succession, its own fitting and needful seasons,
either through a more direct radiation from over-
head or by a longer tarrying of the sun above
the horizon.
Around these poles of the ecliptic the bearing
of the earth's poles rotates, and because of this
motion we have the precession of the equinoxes.
CHAPTER 8. Of the precession of the equinoxes by
reason of the magnetic movement of the earth's poles
in the arctic and antarctic circle of the zodiac
THE early astronomers, not noting the inequal-
ity of years, made no distinction between the
equinoctial or solstitial revolving year and the
year determined from a fixed star. They also
deemed the Olympian years, which were reck-
oned from the rising of the Dog Star, or Sirius
to be the same as those reckoned from the sol-
stice. Hipparchus the Rhodian was the first to
notice that there is a difference between the two,
and found another year, calculated from fixed
stars, of greater length than the equinoctial or
solstitial: hence he supposed that the stars too
have a consequent motion, though a very slow
one, nor readily noticeable. After Hipparchus,
Menelaus, a Roman geometer, then Ptolemy,
and a long time afterward, Machometes Aracen-
sis and several others, in all their writings have
held that the fixed stars and the whole firmament
have a consequent forward movement (in conse-
quentia procedere), for they contemplated the
heavens and not the earth, and knew nothing of
the magnetic inclination. But we will prove that
this motion proceeds from a certain revolution
of the earth's axis, and that the eighth sphere,
so called, the firmament, or aplanes, with its or-
nament of innumerable globes and stars (the
distances of which from earth have never been
by any man demonstrated, nor ever can be),
does not revolve. And surely it must seem more
probable that the appearances of the heavens
should be produced by a deflection and inclina-
tion of the small body, the earth, than by a
WILLIAM GILBERT
whirling of the whole system of the universe—
especially as this movement is ordered for the
good of the earth alone, and is of no benefit at
all to the fixed stars or the planets. For by this
motion the rising and setting of stars in all hori-
zons are changed, as also their culminations in
the zenith, so that stars that once were vertical
are now some degrees distant from the zenith.
Provision has been made by nature for the earth's
soul or its magnetic energy — j ust as in attemper-
ing, receiving, and diverting the sun's rays and
light in fitting seasons, it was necessary that the
bearings of the earth's pole should be 23 degrees
and more distant from the poles of the ecliptic;
so that now in regulating and in receiving in due
order and succession the luminous rays of the
fixed stars, the earth's poles should revolve at
the same distance from the ecliptic in the arctic
circle of the ecliptic, or rather that they should
creep with slow gait, because the actions of the
stars do not always persist in the same parallel
circles, but have a slower change; for the influ-
ences of the stars are not so powerful that the
desired course should be more rapid. So the axis
is inflected slowly, and the rays of the stars are
changed in such length of time as the diameter
of the arctic or polar circle extends; hence the
star in the extremity of the tail of Cynosura,
which once (i.e., in the time of Hipparchus) was
12 degrees 24 minutes distant from the pole of
the world or from the point which the earth's
pole regarded, now is distant from it only 2 de-
grees 52 minutes; hence from its nearness to the
pole it is called by the moderns the Pole Star.
It will not be only J/£ degree from the pole, but
thereafter will begin to recede till it reaches a
distance of 48 degrees; that, according to the
Prutenic tables,1 will be A. D.I 5,000. So the bright
star (which for us here, in southern Britain, now
almost culminates) will in time come within five
degrees of the world's pole. Thus do all the stars
change their light rays at the earth's surface, be-
cause of this admirable magnetic inflection of
the earth's axis. Hence the ever new changes of
the seasons; hence are regions more or less fruit-
ful, more or less sterile; hence changes in the
character and the manners of nations, in govern-
ments and in laws, according to the power of the
fixed stars, the strength thence derived or lost,
and according to the individual and specific na-
ture of the fixed stars as they culminate; or the
1 The Prutenic (Prussian) Astronomical Tables based
upon the observations of Copernicus, Hipparchus, and
Ptolemy, were the result of seven years' labour on part of
the German astronomer Erasmus Reinhold, who named
the work after his benefactor, Albert, Duke of Prussia.
effects may be due to their risings and settings
or to new conjunctions in the meridian.
The precession of the equinoxes from the equal
motion of the earth's pole in the zodiacal circle
is here demonstrated. Let A BCD be the eclip-
N
tic; IEG the Arctic zodiacal circle. Now if the
earth's pole looks toward E, then the equinoxes
are at D, C. Suppose this to be in the time of
Metho,'2 when the horns of Aries were in the
equinoctial colure.3 But if the earth's pole has
advanced to /, then K, L will be the equinoxes,
and stars in the ecliptic C will seem to have
moved forward over the whole arc KC, follow-
ing the signs; L advances by precession over the
arc DL, counter to the order of the signs; but
the opposite would be the case if the point G
were to regard the earth's poles, and the motion
be from E toward G; for then M, W would be the
equinoxes, and the fixed stars would anticipate
at Cand D, counter to the order of the signs.
CHAPTER 9. Of the anomaly of the precession of the
equinoxes and of the obliquity of the zodiac
THE change in the equinoxes is not always equal,
but becomes sometimes more rapid, sometimes
more slow; for the earth's poles travel unequally
2 The celebrated astronomer Meton flourished at Ath-
ens 432-430 B. c. The mean length of the Metonic Cycle,
or Metonic year, was 6939 X days, which coincides with
19 Julian Years and nearly corresponds to 235 lunations.
An improvement on the Metonic Cycle was proposed by
Calippus of Cyzicus, a disciple of Plato. The Cahppic Per-
iod consisted of 76 years, representing four Metonic Cy-
cles, or about 940 complete lunations, io2r n^dal and
1016 complete sidereal revolutions.
3 The colure is one of two great circles which intersect
at right angles in the poles of the equator.
ON THE LOADSTONE
119
in the Arctic and in the Antarctic zodiacal circle,
and recede from the middle line on both sides;
hence the obliquity of the zodiac seems to change
to the equator. And when this became known
through protracted observations, it was appar-
ent that the true equinoctial points were elon-
gated from the mean equinoctial points 70 min-
utes to one side or the other in the greatest pro-
staphaeresi\ while the solstices either approach
the equator equally by 1 2 minutes or recede to
the same extent; so that the nearest approach is
23 deg. 28 min. and the greatest elongation 23
deg. 52 min. Astronomers in accounting for this
inequality of precession and of declination of
the tropics have offered various theories. Thebi-
tius,1 to establish a law for these great inequali-
ties in the movements of the stars, held that the
eighth sphere does not advance by continued
motion from west to east, but that it has a sort
of tremulous motion whereby the leading stars
in Aries and in Libra of the eighth heavens de-
scribe around the leading stars of Aries and Lib-
ra of the ninth sphere certain small circles with
diameters equal to about nine degrees. But as
this "motion of trepidation" is full of absurdities
and impossible motions, this movement has gone
out of fashion. Other astronomers, therefore,
are compelled to ascribe motion
to the eighth sphere, and atop of
this to construct a ninth heaven,
nay a tenth and an eleventh. We
must pardon slips in mathemati-
cians, for one may be permitted in
the case of movements difficult to
account for to offer any hypothe-
ses whatever in order to establish
a law and to bring in a rule that
will make the facts agree. But the
philosopher never can admit such
enormous and monstrous celestial
constructions.
Now though we see in all this
how loath these mathematicians
are to ascribe any motion to the
earth, which is a very small body,
nevertheless they drive and whirl
the heavens, which are vast and
immense beyond human compre-
hension and human imagination:
they construct three heavens, pos-
tulate three inconceivable mon-
strosities, to account for a few un-
explained motions. Ptolemy, com-
paring with his own observations
those of Timochares and Hippar-
1 See note, Book in, i.
chus, of whom the one lived 260 years before his
day and the other 460 years, deemed this to be
the motion of the eighth sphere and of the whole
firmament, and proved it with many phenome-
na on the poles of the zodiac; and, still thinking
its motion to be equal, he held that the fixed
stars in 100 years travel only one degree beneath
the primwn mobile. Seven hundred and fifty
years after him, Abitegnius found that one de-
gree is travelled over in 66 years, so that the
whole period would be 23,760 years. Alphonsus
would have this motion still slower — i degree 28
minutes in 200 years; and thus would the course
of the fixed stars proceed, but unequally. At last
Copernicus, through his own observations and
those of Timochares, Aristarchus the Samian,
Menelaus, Ptolemy, Machometes Aracensis and
Alphonsus, discovered the anomalies of the mo-
tion of the earth's axis; though I have no doubt
that other anomalies also will appear some cen-
turies hence, for it is difficult, save in periods of
many ages, to note so slow a movement, where-
fore we still are ignorant of the mind of nature,
what she is aiming at through this inequality of
motion. Let A be the pole of the ecliptic, BC
the ecliptic, D the equator; when the earth's
pole regards the point M near the arctic circle of
120
the zodiac let the anomaly of the precession of
the equinox be at F, but when it regards N, let
the anomaly of the precession be at E. So long
as it regards / directly there is observed the
maximum obliquity G in the solstitial colure;
but while it regards L, then there is minimum
obliquity H in the colure of the solstices.
WILLIAM GILBERT
and of the anomaly of the precessions, and of
obliquity. The period of the precession of the
equinoxes is 25,816 Egyptian years; the period
of the obliquity of the zodiac is 3434 years and
a little more; the period of the anomaly of the
precession of the equinoxes is 1717 years and a
little more. If we divide the whole time of the
Copernicus' s intorta corolla in the arctic zodiacal circle
FGB is one half of an arctic circle described
around the pole of the zodiac; ABC is the colure
of the solstices; A the pole of the zodiac; DE
the anomaly of longitude 140 minutes on either
side, with twofold terminus (duplici termino) ;
EC anomaly of obliquity, 24 minutes; B the
greater obliquity, 23 degrees 52 minutes; D the
mean obliquity, 23 degrees 40 minutes; C the
minimum obliquity, 23 degrees 28 minutes.
motion from a to / into eight equal parts, in the
first eighth part the pole travels faster from a to
b\ in the second more slowly from b to c\ in the
third, with the same slowness from c to d\ in the
fourth, more rapidly again from d to e\ in the
fifth, with equal rapidity from e tofi again more
slowly from/ to g; with the same slowness from
g to h\ in the last eighth again more rapidly from
h to /, and this is Copernicus's intorta corolla1
True movement and natural axis (or poles) of the earth
directed toward the arctic circle of the zodiac
Let ai be part of the arctic circle of the
zodiac in which is performed one period of the
obliquity. From a to e is the period of the anom-
aly or variation of the precession of the equi-
noxes, ai is the curved line described by the
earth's pole in a true motion made up of three
motions, />., of the motion of the precessions,
with mean motion fused into a curved line, which
is the true path of the motion. And so the pole
1 Copernicus, Revolutions of the Heavenly Spheres, 66, 67 :
the intorta corolla is not an inverted but an irregular
crown: a figure representing the successive positions pro-
duced by the projection of the earth's pole upon the stel-
lar sphere, resembling a crown, but distorted by the ir-
regularities of motion.
ON THE LOADSTONE
reaches the extreme limit of variation of the
precession of the equinoxes twice, but the limit
of inclination or obliquity once only. Thus do
the moderns, and in particular Copernicus, re-
storer of astronomy, describe the variations of
the movement of the earth's axis, so far as the
same is made possible by the observations of the
ancients down to our day ; but we still lack many
and more exact observations to fix anything pos-
itively as to the anomaly of the movement of
the precessions, as also of the obliquity of the
121
zodiac. For since the time when in various ob-
servations this anomaly was first noted, only
one half of a period of obliquity has passed.
Hence all these points touching the unequal
movement of precession and obliquity are un-
decided and undefined, and so we cannot assign
with certainty any natural causes for the mo-
tion.
Wherefore we here bring to an end and con-
clusion our arguments and experiments magnet-
ical.
GALILEO GALILEI
BIOGRAPHICAL NOTE
GALILEO, 1564-1641
GALILEO GALILEI was born at Pisa, February
15, 1564, the eldest of seven children. His
father, who belonged to a noble but impover-
ished Florentine family, was a cloth merchant
highly reputed for his skill in mathematics and
music. At the age of twelve or thirteen Galileo
was sent to school at the monastery of Vallom-
brosa, where he studied the Latin classics and
acquired a fair command of Greek. He seems
to have been a novice for a short time, but his
father then withdrew him from the charge of
the monks.
In 1581 Galileo was sent to the University of
Pisa to study medicine. His father apparently
hoped to prevent him from following either
mathematics or music, whose unremunerative
character he had experienced. The young Gali-
leo was already known for his proficiency in
music; his judgment in painting was highly
esteemed, and Ludovico Cigoli accredited him
with the success of his paintings; but mathemat-
ics soon had an overwhelming attraction for
him. In his first year at the university Galileo
discovered the isochronism of the pendulum, to
which his attention had been drawn by a swing-
ing lamp in the cathedral, and he applied the
principle in a machine for measuring the pulse
known as thepulsilogta. Although compelled to
leave school in 1585 for want of funds, Galileo
continued his investigations. He shortly after-
wards published an essay describing his inven-
tion of the hydrostatic balance. During 1587
and 1588 he delivered two papers before the
Florentine Academy on the site and dimen-
sions of Dante's Inferno. A treatise written at
this time on the center of gravity in solids won
him the title of "the Archimedes of his time."
Despite his growing fame, Galileo was un-
able to find a means of earning his living until
1589. He tried several times unsuccessfully to
obtain a teaching position, and he had even
planned to seek his fortune in the East before
he was called to the honorable but not lucra-
tive post of mathematical lecturer at the Uni-
versity of Pisa. During the ensuing two years,
1589-91, he conducted experiments on the mo-
tion of felling bodies. His lectures on the im-
port of his discoveries alienated the Aristotelian
members of the faculty, and he further aroused
the anger of the authorities by a burlesque in
which he ridiculed the university regulations.
In 1591 Galileo found it prudent to resign, and
shortly afterwards, he secured the chair of
mathematics at the University of Padua.
Galileo taught at Padua for eighteen years,
from 1592 to 1610, and during that time estab-
lished a European reputation as a scientist and
inventor. His lectures, which were attended by
persons of the highest distinction from all parts
of Europe, proved so popular they were given
in a hall that held two thousand persons. He
wrote numerous treatises, which were circulat-
ed among his pupils, dealing with military ar-
chitecture, gnomonics, the sphere, accelerated
motion, and special problems in mechanics. His
more notable inventions at Padua included a
machine for raising water, a geometrical com-
pass, and an air thermometer. But perhaps his
most famous discovery came in 1609, when,
upon learning that the Dutch were beginning
to manufacture magnifying glasses, he put to-
gether a telescope and turned it for the first
time towards the heavens. In his Sidereus Nun-
cius, published early in 1610, Galileo gave the
first results of this new method of investiga-
tion; he noted the mountainous surface of the
moon, the fact that the Milky Way consists of
stars, and the observation of four of Jupiter's
satellites, which he named the "Medicean
Stars" in honor of the Grand Duke of Tuscany.
Almost immediately, Galileo was nominated
philosopher and mathematician extraordinary
to the grand duke at a large salary and with un-
limited leisure for research.
Galileo did not actively defend the Coperni-
can doctrine until after he had begun to use the
telescope. Although he wrote Kepler as early as
1597 that he had "become a convert to the
opinions of Copernicus many years ago," he
continued to teach the Ptolemaic system
throughout his stay at Padua. But with the dis-
covery of the moons of Jupiter and the phases
of Venus he came to the conclusion that "ail my
life and being henceforth depends" on the es-
125
126
BIOGRAPHICAL NOTE
tablishmcnt of the new theory. Galileo's astro-
nomical discoveries brought him great honor,
and in 1611 he traveled to Rome, where he
gave a highly successful demonstration of the
telescope to the ecclesiastical authorities. But
as soon as he tried to maintain that the Coper-
nican theory could be reconciled with Scrip-
tures, he began to encounter opposition from
the theologians.
The first ecclesiastical attack upon Galileo
occurred in 1614 when he was denounced from
the pulpit in Florence for holding the new as-
tronomical doctrine. Galileo replied by issuing
his Letter to the Grand Duchess Christine of Lor-
raine, in which he strongly supported the words
of Cardinal Baronius that the "Holy Spirit in-
tended to teach us in the Bible how to go to
Heaven, not how the heavens go." This letter
was at once laid before the Inquisition, and in
1615 Galileo was informed by an ecclesiastical
friend in Rome: "You can write as a mathema-
tician and hypothetically, as Copernicus is said
to have done, and you can write freely so long
as you keep out of the sacristy." But early in
1616 the Holy Office condemned two funda-
mental Copernican propositions selected from
Galileo's work On the Sun Spots, and he was
summoned before Cardinal Bellarmine and
warned not to hold or defend the Copernican
theory. Dismayed by the slanders regarding
him, Galileo obtained from the Cardinal a cer-
tificate explaining that he had not been made
to abjure his opinions nor enjoined to perform
salutary penance.
Galileo maintained silence until 1627. In that
year he published // Saggiatore, in which he con-
tended that the new astronomical discoveries
were more in accord with the Copernican than
the Ptolemaic system; he added that, since) the
one theory was condemned by the Church and
the other by reason, a third system would have
to be sought. The book was dedicated to Urban
VIII. It was well received by both ecclesiastical
and scientific authorities, and in the course of
two months Galileo had six audiences with the
pope. Encouraged by this reception, he de-
voted the next eight years to writing his Dia-
logue of the Two Principal Systems of the World
(1632). Upon its publication Galileo was de-
nounced by the ecclesiastical authorities and
summoned for trial before the Holy Office.
He was accused on three charges: that he had
broken his agreement of 1616, that he had
taught the Copernican theory as a truth and
not a hypothesis, and that he inwardly be-
lieved the truth of a doctrine condemned by
the Church. In the trial of 1633 he was found
guilty on the first two charges, but on his as-
sertion that it was never his intention to believe
the truth of the Copernican doctrine after its
condemnation, he was denounced only as "vehe-
mently suspected of heresy" and sentenced to
punishment at the will of the court. Galileo
submitted and made the required recantation.
On being allowed to leave Rome, Galileo
went to Siena and resided for several months in
the house of the archbishop. In December,
1633, he was permitted to return to his villa at
Arcetri, near Florence, where he spent the re-
mainder of his life in retirement according to
the conditions of his release. Here he completed
the Dialogue of the Two New Sciences, in which
he turned back to the scientific investigations
of his youth. The work, which was printed by
the Elzevirs at Leyden in 1638, was considered
by Galileo to be "superior to everything else of
mine hitherto published." His last telescopic
discovery — that of the moon's diurnal and
monthly librations — was made in 1637, only a
few months before he became blind. But blind-
ness was not allowed to interrupt his scientific
correspondence and investigation. He worked
out the application of the pendulum to the
clock, which Huygens was to apply successfully
several years later, and was engaged in dictat-
ing to his disciples, Viviani and Torricelli, his
latest ideas on the theory of impact when he
was seized with fever. He died January 8, 1642,
and was buried in the chapel of Santa Croce in
Florence.
CONTENTS
BIOGRAPHICAL NOTE 125
I. First New Science, Treating of the Resistance which
Solid Bodies Offer to Fracture. First Day 129
II. Concerning the Cause of Cohesion. Second Day 178
III. Second New Science, Treating of Motion, Third Day 197
Uniform Motion 197
Naturally Accelerated Motion 200
IV. Violent Motions. Projectiles. Fourth Day 238
127
Dialogues Concerning the
Two New Sciences
To THE MOST ILLUSTRIOUS LORD COUNT OF NoAILLES
COUNSELLOR OF HIS MOST CHRISTIAN MAJESTY, KNIGHT OF THE ORDER OF
THE HOLY GHOST, FIELD MARSHAL AND COMMANDER, SENESCHAL AND
GOVERNOR OF ROUERGUE, AND HIS MAJESTY'S LIEUTENANT IN
AUVERGNE, MY LORD AND WORSHIPFUL PATRON
MOST ILLUSTRIOUS LORD:
In the pleasure which you derive from the
possession of this work of mine, I recognize your
Lordship's magnanimity. The disappointment
and discouragement I have felt over the ill-for-
tune which has followed my other books are al-
ready known to you. Indeed, I had decided not
to publish any more of my work. And yet in
order to save it from complete oblivion, it seemed
to me wise to leave a manuscript copy in some
place where it would be available at least to
those who follow intelligently the subjects which
I have treated. Accordingly, I chose first to place
my work in your Lordship's hands, asking no
more worthy depository, and believing that, on
account of your affection for me, you would
have at heart the preservation of my studies and
labours. Therefore, when you were returning
home from your mission to Rome, I came to
pay my respects in person as 1 had already done
many times before by letter. At this meeting I
presented to your Lordship a copy of these two
works which at that time I happened to have
ready. In the gracious reception which you gave
these I found assurance of their preservation.
The fact of your carrying them to France and
showing them to friends of yours who are skilled
in these sciences gave evidence that my silence
was not to be interpreted as complete idleness.
A little later, just as I was on the point of send-
ing other copies to Germany, Flanders, Eng-
land, Spain, and possibly to some places in Italy,
I was notified by the Elzevirs that they had
these works of mine in press, and that I ought to
decide upon a dedication and send them a reply
at once. This sudden and unexpected news led
me to think that the eagerness of your Lord-
ship to revive and spread my name by passing
these works on to various friends was the real
cause of their falling into the hands of printers
who, because they had already published other
works of mine, now wished to honour me with a
beautiful and ornate edition of this work. But
these writings of mine must have received addi-
tional value from the criticism of so excellent a
judge as your Lordship, who by the union of
many virtues has won the admiration of all. Your
desire to enlarge the renown of my work shows
your unparalleled generosity and your zeal for
the public welfare which you thought would
thus be promoted. Under these circumstances
it is eminently fitting that I should, in unmis-
takable terms, gratefully acknowledge this gen-
erosity on the part of your Lordship, who has
given to my fame wings that have carried it into
regions more distant than I had dared to hope.
It is, therefore, proper that I dedicate to your
Lordship this child of my brain. To this course
I am constrained not only by the weight of
obligation under which you have placed me,
but also, if I may so speak, by the interest
which I have in securing your Lordship as the
defender of my reputation against adversaries
who may attack it while I remain under your
protection.
And now, advancing under your banner, I
pay my respects to you by wishing that you
may be rewarded for these kindnesses by the
achievement of the highest happiness and great-
ness.
I am your Lordship's
Most devoted Servant,
GALILEO GALILEI
Arcetri, 6 March, 1638
129
FIRST DAY
INTERLOCUTORS: SALVIATI, SAGREDO AND SIMPLICIO
SALVIATI. The constant activity which you Ve-
netians display in your famous arsenal suggests
to the studious mind a large field for investiga-
tion, especially that part of the work which in-
volves mechanics ; for in this department all types
of instruments and machines are constantly be-
ing constructed by many artisans, among whom
there must be some who, partly by inherited
experience and partly by their own observa-
tions, have become highly expert and clever in
explanation.
SAGR. You are quite right. Indeed, I myself,
being curious by nature, frequently visit this
place for the mere pleasure of observing the
work of those who, on account of their superi-
ority over otherartisans, we call "first rankmen."
Conference with them has often helped me in
the investigation of certain effects including not
only those which are striking, but also those
which are recondite and almost incredible. At
times also I have been put to confusion and driv-
en to despair of ever explaining something for
which I could not account, but which my senses
told me to be true. And notwithstanding the
fact that what the old man told us a little while
ago is proverbial and commonly accepted, yet
it seemed to me altogether false, like many an-
other saying which is current among the igno-
rant; for I think they introduce these expres
sions in order to give the appearance of know-
ing something about matters which they do not
understand.
SALV. You refer, perhaps, to that last remark
of his when we asked the reason why they em-
ployed stocks, scaffolding, and bracing of larger
dimensions for launching a big vessel than they
do for a small one; and he answered that they
did this in order to avoid the danger of the ship
parting under its own heavy weight, a danger
to which small boats are not subject ?
SAGR. Yes, that is what I mean; and I refer
especially to his last assertion which I have al-
ways regarded as false, though current, opinion;
namely, that in speaking of these and other sim-
ilar machines one cannot argue from the small
to the large, because many devices which suc-
ceed on a small scale do not work on a large
scale. Now, since mechanics has its foundation
in geometry, where mere size cuts no figure, I
do not see that the properties of circles, triangles,
cylinders, cones, and other solid figures will
change with their size. If, therefore, a large ma-
chine be constructed in such a way that its parts
bear to one another the same ratio as in a smaller
one, and if the smaller is sufficiently strong for
the purpose for which it was designed, I do not
see why the larger also should not be able to
withstand any severe and destructive tests to
which it may be subjected.
SAI/V. The common opinion is here absolutely
wrong. Indeed, it is so far wrong that precisely
the opposite is true, namely, that many ma-
chines can be constructed even more perfectly
on a large scale than on a small; thus, for in-
stance, a clock which indicates and strikes the
hour can be made more accurate on a large scale
than on a small. There are some intelligent peo-
ple who maintain this same opinion, but on more
reasonable grounds, when they cut loose from
geometry and argue that the better perform-
ance of the large machine is owing to the imper-
fections and variations of the material. Here I
trust you will not charge me with arrogance if I
say that imperfect ion sin the material, even those
which are great enough to invalidate the clearest
mathematical proof, are not sufficient to explain
the deviations observed between machines in
the concrete and in the abstract. Yet I shall say
it and will affirm that, even if the imperfections
did not exist and matter were absolutely per-
fect, unalterable, and free from all accidental
variations, still the mere fact that it is matter
makes the larger machine, built of the same ma-
terial and in the same proportion as the smaller,
correspond with exactness to the smaller in every
respect except that it will not be so strong or so
resistant against violent treatment; the larger
the machine, the greater its weakness. Since I
assume matter to be unchangeable and always
the same, it is clear that we are no less able to
GALILEO GALILEI
treat this constant and invariable property in a
rigid manner than if it belonged to simple and
pure mathematics. Therefore, Sagredo, you
would do well to change the opinion which you,
and perhaps also many other students of me-
chanics, have entertained concerning the abil-
ity of machines and structures to resist external
disturbances, thinking that when they are built
of the same material and maintain the same ra-
tio between parts, they are able equally, or rath-
er proportionally, to resist or yield to such ex-
ternal disturbances and blows. For we can dem-
onstrate by geometry that the large machine is
not proportionately stronger than the small.
Finally, we may say that, for every machine and
structure, whether artificial or natural, there is
set a necessary limit beyond which neither art
nor nature can pass; it is here understood, of
course, that the material is the same and the
proportion preserved.
SAGR. My brain already reels. My mind, like
a cloud momentarily illuminated by a lightning-
flash, is for an instant filled with an unusual light,
which now beckons to me and which now sud-
denly mingles and obscures strange, crude ideas.
From what you have said it appears to me im-
possible to build two similar structures of the
same material, but of different sizes and have
them proportionately strong; and if this were
so, it would not be possible to find two single
poles made of the same wood which shall be
alike in strength and resistance but unlike in
size.
SALV. So it is, Sagredo. And to make sure
that we understand each other, I say that if we
take a wooden rod of a certain length and size,
fitted, say, into a wall at right angles, i.e., paral-
lel to the horizon, it may be reduced to such a
length that it will just support itself; so that if a
hair's breadth be added to its length it will break
under its own weight and will be the only rod
of the kind in the world. Thus if, for instance,
its length be a hundred times its breadth, you
will not be able to find another rod whose length
is also a hundred times its breadth and which,
like the former, is just able to sustain its own
weight and no more: all the larger ones will
break while all the shorter ones will be strong
enough to support something more than their
own weight. And this which I have said about
the ability to support itself must be understood
to apply also to other tests; so that if a piece of
scantling will carry the weight of ten similar to
itself, a beam having the same proportions will
not be able to support ten similar beams.
Please observe, gentlemen, how facts which
at first seem improbable will, even on scant ex-
planation, drop the cloak which has hidden them
and stand forth in naked and simple beauty.
Who does not know that a horse falling from a
height of three or four cubits will break his bones,
while a dog falling from the same height or a cat
from a height of eight or ten cubits will suffer
no injury? Equally harmless would be the fall
of a grasshopper from a tower or the fall of an
ant from the distance of the moon. Do not chil-
dren fall with impunity from heights which
would cost their elders a broken leg or perhaps
a fractured skull? And just as smaller animals
are proportionately stronger and more robust
than the larger, so also smaller plants are able to
stand up better than larger. I am certain you
both know that an oak two hundred cubits high
would not be able to sustain its own branches if
they were distributed as in a tree of ordinary
size; and that nature cannot produce a horse as
large as twenty ordinary horses or a giant ten
times taller than an ordinary man unless by mir-
acle or by greatly altering the proportions of
his limbs and especially of his bones, which would
have to be considerably enlarged over the or-
dinary. Likewise the current belief that, in the
case of artificial machines the very large and the
small are equally feasible and lasting is a manifest
error. Thus, for example, a small obelisk or col-
umn or other solid figure can certainly be laid
down or se t up wi thou t danger of breaking, while
the very large ones will go to pieces under the
slightest provocation, and that purely on ac-
count of their own weight. And here I must re-
late a circumstance which is worthy of your at-
tention as indeed are all events which happen
contrary to expectation, especially when a pre-
cautionary measure turns out to be a cause of
disaster. A large marble column was laid out so
that its two ends rested each upon a piece of
beam; a little later it occurred to a mechanic
that, in order to be doubly sure of its not break-
ing in the middle by its own weight, it would be
wise to lay a third support midway; this seemed
to all an excellent idea; but the sequel showed
that it was quite the opposite, for not many
months passed before the column was found
cracked and broken exactly above the new mid-
dle support.
SIMP. A very remarkable and thoroughly un-
expected accident, especially if caused by plac-
ing that new support in the middle.
SALV. Surely this is the explanation, and the
moment the cause is known our surprise vanish-
es; for when the two pieces of the column were
placed on level ground it was observed that one
THE TWO NEW SCIENCES
133
of the end beams had, after a long while, be-
come decayed and sunken, but that the middle
one remained hard and strong, thus causing one
half of the column to project in the air without
any support. Under these circumstances the body
therefore behaved differently from what it would
have done if supported only upon the first beams;
because no matter how much they might have
sunken the column would have gone with them.
This is an accident which could not possibly
have happened to a small column, even though
made of the same stone and having a length
corresponding to its thickness, /'. e., preserving
the ratio between thickness and length found in
the large pillar.
SAGR. I am quite convinced of the facts of the
case, but I do not understand why the strength
and resistance are not multiplied in the same
proportion as the material; and I am the more
puzzled because, on the contrary, I have noticed
in other cases that the strength and resistance
against breaking increase in a larger ratio than
the amount of material. Thus, for instance, if
two nails be driven into a wall, the one which is
twice as big as the other will support not only
twice as much weight as the other, but three or
four times as much.
SALV. Indeed you will not be far wrong if you
say eight times as much; nor does this phenom-
enon contradict the other even though in ap-
pearance they seem so different.
SAGR. Will you not then, Salviati, remove
these difficulties and clear away these obscuri-
ties if possible: for I imagine that this problem
of resistance opens up a field of beautiful and
useful ideas; and if you are pleased to make this
the subject of to-day's discourse you will place
Simplicio and me under many obligations.
SALV. I am at your service if only I can call to
mind what I learned from our Academician1 who
had thought much upon this subject and accord-
ing to his custom had demonstrated everything
by geometrical methods so that one might fairly
call this a new science. For, although some of his
conclusions had been reached by others, first of
all by Aristotle, these are not the most beautiful
and, what is more important, they had not been
proven in a rigid manner from fundamental prin-
ciples. Now, since I wish to convince you by
demonstrative reasoning rather than to persuade
you by mere probabilities, I shall suppose that
you are familiar with present-day mechanics so
far as it is needed in our discussion. First of all
it is necessary to consider what happens when a
1 Galileo: the author frequently refers to himself un-
der this name. TRANS.
piece of wood or any other solid which coheres
firmly is broken; for this is the fundamental
fact, involving the first and simple principle
which we must take for granted as well known.
To grasp this more clearly, imagine a cylinder
or prism, AB, made of wood or other solid co-
herent material. Fasten the upper end, A, so
that the cylinder hangs vertically. To the lower
end, Bj attack the weight C. It is clear that how-
ever great they may be, the tenacity and co-
herence between the parts of this solid, so long
as they are not infinite, can be overcome by the
pull of the weight C, a weight which can be in-
creased indefinitely until finally the solid breaks
like a rope. And as in the case of the rope whose
strength we know to be derived from a multi-
tude of hemp threads which compose it, so in
the case of the wood, we observe its fibres and
filaments run lengthwise and render it much
stronger than a hemp rope of the same thick-
ness. But in the case of a
stone or metallic cylinder
where the coherence seems
to be still greater the ce-
ment which holds the parts
together must be some-
thing other than filaments
and fibres; and yet even
this can be broken by a
strong pull.
SIMP. If this matter be
as you say I can well under-
stand that the fibres of the
wood, being as long as the
piece of wood itself, render
it strong and resistant a-
gainst large forces tend-
ing to break it. But how
can one make a rope one
hundred cubits long out of
hempen fibres which are
Fig. i
not more than two or three cubits long, and
still give it so much strength ? Besides, I should
be glad to hear your opinion as to the manner in
which the parts of metal, stone, and other ma-
terials not showing a filamentous structure are
put together; for, if I mistake not, they exhibit
even greater tenacity.
SALV. To solve the problems which you raise
it will be necessary to make a digression into
subjects which have little bearing upon our pres-
ent purpose.
SAGR. But if, by digressions, we can reach new
truth, what harm is there in making one now,
so that we may not lose this knowledge, remem-
bering that such an opportunity, once omitted,
GALILEO GALILEI
may not return; remembering also that we are
not tied down to a fixed and brief method but
that we meet solely for our own entertainment ?
Indeed, who knows but that we may thus fre-
quently discover something more interesting
and beautiful than thesolution originally sought?
I beg of you, therefore, to grant the request of
Simplicio, which is also mine; for I am no less
curious and desirous than he to learn what is the
binding material which holds together the parts
of solids so that they can scarcely be separated.
This information is also needed to understand
the coherence of the parts of fibres themselves
of which some solids are built up.
SALV. I am at your service, since you desire it.
The first question is, How are fibres, each not
more than twoor three cubits in length, so tightly
bound together in the case of a rope one hun-
dred cubits long that great force is required to
break it ?
Now tell me, Simplicio, can you not hold a
hempen fibre so tightly between your fingers
that I, pulling by the other end, would break it
before drawing it away from you? Certainly
you can. And now when the fibres of hemp are
held not only at the ends, but are grasped by
the surrounding medium throughout their en-
tire length is it not manifestly more difficult to
tear them loose from what holds them than to
break them? But in the case of the rope the
very act of twisting causes the threads to bind
one another in such a way that when the rope is
stretched with a great force the fibres break
rather than separate from each other.
At the point where a rope parts the fibres are,
as everyone knows, very short, nothing like a
cubit long, as they would be if the parting of
the rope occurred, not by the breaking of the
filaments, but by their slipping one over the
other.
SAGR. In confirmation of this it may be re-
marked that ropes sometimes break not by a
lengthwise pull but by excessive twisting. This,
it seems to me, is a conclusive argument because
the threads bind one another so tightly that the
compressing fibres do not permit those which
are compressed to lengthen the spirals even that
little bit by which it is necessary for them to
lengthen in order to surround the rope which,
on twisting, grows shorter and thicker.
SALV. You are quite right. Now see how one
fact suggests another. The thread held between
the fingers does not yield to one who wishes to
draw it away even when pulled with consider-
able force, but resists because it is held back by
a double compression, seeing that the upper fin-
ger presses against the lower as hard as the lower
against the upper. Now, if we could retain only
one of these pressures there is no doubt that
only half the original resistance would remain;
but since we are not able, by lifting, say, the
upper finger, to remove one of these pressures
without also removing the other, it becomes
necessary to preserve one of them by means of a
new device which causes the thread to press it-
self against the finger or against some other solid
body upon which it rests; and thus it is brought
Fig. 2
about that the very force which pulls it in order
to snatch it away compresses it more and more
as the pull increases. This is accomplished by
wrapping the thread around the solid in the
manner of a spiral; and will be better under-
stood by means of a figure. Let AB and CD be
two cylinders between which is stretched the
thread EF: and for the sake of greater clearness
we will imagine it to be a small cord. If these
two cylinders be pressed strongly together, the
cord EF, when drawn by the end F, will un-
doubtedly stand a considerable pull before it
slips between the two compressing solids. But if
we remove one of these cylinders the cord,
though remaining in contact with the other,
will not thereby be prevented from slipping
freely. On the other hand, if one holds the cord
loosely against the top of the cylinder A, winds
it in the spiral form AFLOTR, and then pulls it
by the end R, it is evident that the cord will be-
gin to bind the cylinder; the greater the number
THE TWO NEW SCIENCES
of spirals the more tightly will the cord be pressed
against the cylinder by any given pull. Thus as
the number of turns increases, the line of con-
tact becomes longer and in consequence more
resistant; so that the cord slips and yields to the
tractive force with increasing difficulty.
Is it not clear that this is precisely the kind of
resistance which one meets in the case of a thick
hemp rope where the fibres form thousands and
thousands of similar spirals ? And, indeed, the
binding effect of these turns is so great that a
few short rushes woven together into a few in-
terlacing spirals form one of the strongest of
ropes which I believe they call pack rope.
SAGR. What you say has cleared up two points
which I did not previously understand. One fact
is how two, or at most three, turns of a rope
around the axle of a windlass cannot only hold
it fast, but can also prevent it from slipping
when pulled by the immense force of the weight
which it sustains; and moreover how, by turn-
ing the windlass, this same axle, by mere friction
of the rope around it, can wind up and lift huge
stones while a mere boy is able to
handle the slack of the rope. The
other fact has to do with a simple
but clever device, invented by a
young kinsman of mine, for the
purpose of descending from a win-
dow by means of a rope without lac-
erating the palms of his hands, as
had happened to him shortly before
and greatly to his discomfort. A
small sketch will make this clear.
He took a wooden cylinder, AB,
about as thick as a walking stick
and about one span long: on this
he cut a spiral channel of about one
> B turn and a half, and large enough
to just receive the rope which he
wished to use. Having introduced
*l& 3 the rope at the end A and led it out
again at the end B, he enclosed both the cylinder
and the rope in a case of wood or tin, hinged
along the side so that it could be easily opened
and closed. After he had fastened the rope to a
firm support above, he could, on grasping and
squeezing the case with both hands, hang by his
arms. The pressure on the rope, lying between
the case and the cylinder, was such that he
could, at will, either grasp the case more tightly
and hold himself from slipping, or slacken his
hold and descend as slowly as he wished.
SALV. A truly ingenious device! I feel, how-
ever, that for a complete explanation other con-
siderations might well enter; yet I must not now
digress upon this particular topic since you are
waiting to hear what I think about the breaking
strength of other materials which, unlike ropes
and most woods, do not show a filamentous struc-
ture. The coherence of these bodies is, in my
estimation, produced by other causes which may
be grouped under two heads. One is that much-
talked-of repugnance which nature exhibits to-
wards a vacuum; but this horror of a vacuum
not being sufficient, it is necessary to introduce
another cause in the form of a gluey or viscous
substance which binds firmly together the com-
ponent parts of the body.
First I shall speak of the vacuum, demonstrat-
ing by definite experiment the quality and quan-
tity of its force. If you take two highly polished
and smooth plates of marble, metal, or glass and
place them face to face, one will slide over the
other with the greatest ease, showing conclu-
sively that there is nothing of a viscous nature
between them. But when you attempt to sep-
arate them and keep them at a constant dis-
tance apart, you find the plates exhibit such a
repugnance to separation that the upper one
will carry the lower one with it and keep it lifted
indefinitely, even when the latter is big and
heavy.
This experiment shows the aversion of nature
for empty space, even during the brief moment
required for the outside air to rush in and fill up
the region between the two plates. It is also ob-
served that if two plates are not thoroughly pol-
ished, their contact is imperfect so that when
you attempt to separate them slowly the only
resistance offered is that of weight; if, however,
the pull be sudden, then the lower plate rises,
but quickly falls back, having followed the up-
per plate only for that very short interval of
time required for the expansion of the small
amount of air remaining between the plates, in
consequence of their not fitting, and for the en-
trance of the surrounding air. This resistance
which is exhibited between the two plates is
doubtless likewise present between the parts of
a solid, and enters, at least in part, as a concomi-
tant cause of their coherence.
SAGR. Allow me to interrupt you for a mo-
ment, please; for I want to speak of something
which just occurs to me, namely, when I see how
the lower plate follows the upper one and how
rapidly it is lifted, I feel sure that, contrary to
the opinion of many philosophers, including per-
haps even Aristotle himself, motion in a vacu-
um is not instantaneous. If this were so the two
plates mentioned above would separate without
any resistance whatever, seeing that the same
'36
GALILEO GALILEI
instant of time would suffice for their separa-
tion and for the surrounding medium to rush in
and fill the vacuum between them. The fact
that the lower plate follows the upper one al-
lows us to infer, not only that motion in a vacu-
um is not instantaneous, but also that, between,
the two plates, a vacuum really exists, at least
for a very short time, sufficient to allow the sur-
rounding medium to rush in and fill the vacu-
um; for if there were no vacuum there would be
no need of any motion in the medium. One
must admit then that a vacuum is sometimes
produced by violent motion or contrary to the
laws of nature, (although in my opinion nothing
occurs contrary to nature except the impossible,
and that never occurs).
But here another difficulty arises. While ex-
periment convinces me of the correctness of this
conclusion, my mind is not entirely satisfied as
to the cause to which this effect is to be attri-
buted. For the separation of the plates precedes
the formation of the vacuum which is produced
as a consequence of this separation; and since it
appears to me that, in the order of nature, the
cause must precede the effect, even though it
appears to follow in point of time, and since
every positive effect must have a positive cause,
I do not see how the adhesion of two plates and
their resistance to separation— actual facts— can
be referred to a vacuum as cause when this vacu-
um is yet to follow. According to the infallible
maxim of the Philosopher, the non-existent can
produce no effect.
SIMP. Seeing that you accept this axiom of
Aristotle, I hardly think you will reject another
excellent and reliable maxim of his, namely, Na-
ture undertakes only that which happens with-
out resistance; and in this saying, it appears to
me, you will find the solution of your difficulty.
Since nature abhors a vacuum, she prevents that
from which a vacuum would follow as a neces-
sary consequence. Thus it happens that nature
prevents the separation of the two plates.
SAGR. Now admitting that what Simplicio
says is an adequate solution of my difficulty, it
seems to me, if I may be allowed to resume my
former argument, that this very resistance to a
vacuum ought to be sufficient to hold together
the parts either of stone or of metal or the parts
of any other solid which is knit together more
strongly and which is more resistant to separa-
tion. If for one effect there be only one cause, or
if, more being assigned, they can be reduced to
one, then why is not this vacuum which really
exists a sufficient cause for all kinds of resistance ?
SALV. I do not wish just now to enter this
discussion as to whether the vacuum alone is
sufficient to hold together the separate parts of
a solid body; but I assure you that the vacuum
which acts as a sufficient cause in the case of the
two plates is not alone sufficient to bind togeth-
er the parts of a solid cylinder of marble or metal
which, when pulled violently, separates and di-
vides. And now if I find a method of distinguish-
ing this well known resistance, depending upon
the vacuum, from every other kind which might
increase the coherence, and if I show you that
the aforesaid resistance alone is not nearly suf-
ficient for such an effect, will you not grant that
we are bound to introduce another cause ? Help
him, Simplicio, since he does not know what
reply to make.
SIMP. Surely, Sagredo's hesitation must be
owing to another reason, for there can be no
doubt concerning a conclusion which is at once
so clear and logical.
SAGR. You have guessed rightly, Simplicio. I
was wondering whether, if a million of gold each
year from Spain were not sufficient to pay the
army, it might not be necessary to make provi-
sion other than small coin for the pay of the
soldiers.
But go ahead, Salviati; assume that I admit
your conclusion and show us your method of
separating the action of the vacuum from other
causes; and by measuring it show us how it is
not sufficient to produce the effect in question.
SALV. Your good angel assist you. I will tell
you how to separate the force of the vacuum
from the others, and afterwards how to measure
it. For this purpose let us consider a continuous
substance whose parts lack all resistance to sep-
aration except that derived from a vacuum, such
as is the case with water,
a fact fully demonstrated
by our Academician in
one of his treatises. When-
ever a cylinder of water is
subjected to a pull and
offers a resistance to the
separation of its parts this
can be attributed to no
other cause than the re-
sistance of the vacuum.
In order to try such an
experiment I have in-
vented a device which I
can better explain by
means of a sketch than by
mere words. Let CABD
represent the cross section
ofacylindercitherofmet- Fig. 4
THE TWO NEW SCIENCES
'37
al or, preferably, of glass, hollow inside and ac-
curately turned. Into this is introduced a per-
fectly fitting cylinder of wood, represented in
cross section by EGHF, and capable of up-and-
down motion. Through the middle of this cyl-
inder is bored a hole to receive an iron wire, car-
rying a hook at the end K, while the upper end
of the wire, /, is provided with a conical head.
The wooden cylinder is countersunk at the top
so as to receive, with a perfect fit, the conical
head / of the wire, IK, when pulled down by the
end A:.
Now insert the wooden cylinder EH in the
hollow cylinder AD, so as not to touch the up-
per end of the latter but to leave free a space of
two or three finger- breadths; this space is to be
filled with water by holding the vessel with the
mouth CD upwards, pushing down on the stop-
per EH, and at the same time keeping the con-
ical head of the wire, /, away from the hollow
portion of the wooden cylinder. The air is thus
allowed to escape alongside the iron wire (which
does not make a close fit) as soon as one presses
down on the wooden stopper. The air having
been allowed to escape and the iron wire hav-
ing been drawn back so that it fits snugly against
the conical depression in the wood, invert the
vessel, bringing it mouth downwards, and hang
on the hook K a vessel which can be filled with
sand or any heavy material in quantity suffi-
cient to finally separate the upper surface of the
stopper, EF, from the lower surface of the water
to which it was attached only by the resistance
of the vacuum. Next weigh the stopper and
wire together with the attached vessel and its
contents; we shall then have the force of the
vacuum. If one attaches to a cylinder of marble
or glass a weight which, together with the weight
of the marble or glass itself, is just equal to the
sum of the weights before mentioned, and if
breaking occurs we shall then be justified in say-
ing that the vacuum alone holds the parts of the
marble and glass together; but if this weight
does not suffice and if breaking occurs only after
adding, say, four times this weight, we shall then
be compelled to say that the vacuum furnishes
only one fifth of the total resistance.
SIMP. No one can doubt the cleverness of the
device; yet it presents many difficulties which
make me doubt its reliability. For who will as-
sure us that the air does not creep in between
the glass and stopper even if it is well packed
with tow or other yielding material ? I question
also whether oiling with wax or turpentine will
suffice to make the cone, I, fit snugly on its seat.
Besides, may not the parts of the water expand
and dilate ? Why may not the air or exhalations
or some other more subtile substances penetrate
the pores of the wood, or even of the glass it-
self?
SALV. With great skill indeed has Simplicio
laid before us the difficulties; and he has even
partly suggested how to prevent the air from
penetrating the wood or passing between the
wood and glass. But now let me point out that,
as our experience increases, we shall learn whether
or not these alleged difficulties really exist. For
if, as is the case with air, water is by nature ex-
pansible, although only under severe treatment,
we shall see the stopper descend; and if we put a
small excavation in the upper part of the glass
vessel, such as indicated by V, then the air or
any other tenuous and gaseous substance, which
might penetrate the pores of glass or wood, would
pass through the water and collect in this re-
ceptacle V. But if these things do not happen
we may rest assured that our experiment has
been performed with proper caution; and we
shall discover that water does not dilate and
that glass does not allow any material, however
tenuous, to penetrate it.
SAGR. Thanks to this discussion, I have learned
the cause of a certain effect which I have long
wondered at and despaired of understanding. I
once saw a cistern which had been provided with
a pump under the mistaken impression that the
water might thus be drawn with less effort or in
greater quantity than by means of the ordinary
bucket. The stock of the pump carried its suck-
er and valve in the upper part so that the water
was lifted by attraction and not by a push as is
the case with pumps in which the sucker is placed
lower down. This pump worked perfectly so
long as the water in the cistern stood above a
certain level; but below this level the pump
failed to work. When I first noticed this phe-
nomenon I thought the machine was out of or-
der; but the workman whom I called in to repair
it told me the defect was not in the pump but in
the water which had fallen too low to be raised
through such a height; and he added that it was
not possible, either by a pump or by any other
machine working on the principle of attraction,
to lift water a hair's breadth above eighteen
cubits; whether the pump be large or small this
is the extreme limit of the lift. Up to this time I
had been so thoughtless that, although I knew
a rope, or rod of wood, or of iron, if sufficiently
long, would break by its own weight when held
by the upper end, it never occurred to me that
the same thing would happen, only much more
easily, to a column of water. And really is not
138
GALILEO GALILEI
that thing which is attracted in the pump a col-
umn of water attached at the upper end and
stretched more and more until finally a point is
reached where it breaks, like a rope, on account
of its excessive weight ?
SALV. That is precisely the way it works; this
fixed elevation of eighteen cubits is true for any
quantity of water whatever, be the pump large
or small or even as fine as a straw. We may there-
fore say that, on weighing the water contained
in a tube eighteen cubits long, no matter what
the diameter, we shall obtain the value of the
resistance of the vacuum in a cylinder of any
solid material having a bore of this same diame-
ter. And having gone so far, let us see how easy
it is to find to what length cylinders of metal,
stone, wood, glass, etc., of any diameter can be
elongated without breaking by their own weight.
Take for instance a copper wire of any length
and thickness; fix the upper end and to the other
end attach a greater and greater load until final-
ly the wire breaks; let the maximum load be,
say, fifty pounds. Then it is clear that if fifty
pounds of copper, in addition to the weight of
the wire itself which may be, say, y& ounce, is
drawn out into wire of this same size we shall
have the greatest length of this kind of wire
which can sustain its own weight. Suppose the
wire which breaks to be one cubit in length and
y& ounce in weight; then since it supports 50
Ibs. in addition to its own weight, /'. £., 4800
eighths-of-an-ounce, it follows that all copper
wires, independent of size, can sustain them-
selves up to a length of 4801 cubits and no more.
Since then a copper rod can sustain itsown weight
up to a length of 4801 cubits it follows that that
part of the breaking strength which depends
upon the vacuum, comparing it with the re-
maining factors of resistance, is equal to the
weight of a rod of water, eighteen cubits long
and as thick as the copper rod. If, for example,
copper is nine times as heavy as water, the break-
ing strength of any copper rod, in so far as it de-
pends upon the vacuum, is equal to the weight
of two cubits of this same rod. By a similar
method one can find the maximum length of
wire or rod of any material which will just sus-
tain its own weight, and can at the same time
discover the part which the vacuum plays in its
breaking strength.
SAGR. It still remains for you to tell us upon
what depends the resistance to breaking, other
than that of the vacuum; what is the gluey or
viscous substance which cements together the
parts of the solid ? For I cannot imagine a glue
that will not burn up in a highly heated furnace
in two or three months, or certainly within ten
or a hundred. For if gold, silver and glass are
kept for a long while in the molten state and are
removed from the furnace, their parts, on cool-
ing, immediately reunite and bind themselves
together as before. Not only so, but whatever
difficulty arises with respect to the cementation
of the parts of the glass arises also with regard
to the parts of the glue; in other words, what is
that which holds these parts together so firmly ?
SALV. A little while ago, I expressed the hope
that your good angel might assist you. I now
find myself in the same straits. Experiment leaves
no doubt that the reason why two plates cannot
be separated, except with violent effort, is that
they are held together by the resistance of the
vacuum; and the same can be said of two large
pieces of a marble or bronze column. This being
so, I do not see why this same cause may not ex-
plain the coherence of smaller parts and indeed
of the very smallest particles of these materials.
Now, since each effect must have one true and
sufficient cause and since I find no other cement,
am I not justified in trying to discover whether
the vacuum is not a sufficient cause ?
SIMP. But seeing that you have already proved
that the resistance which the large vacuum of-
fers to the separation of two large parts of a solid
is really very small in comparison with that co-
hesive force which binds together the most mi-
nute parts, why do you hesitate to regard this
latter as something very different from the for-
mer?
SALV. Sagredo has already answered this ques-
tion when he remarked that each individual sol-
dier was being paid from coin collected by a
general tax of pennies and farthings, while even
a million of gold would not suffice to pay the en-
tire army. And who knows but that there may
be other extremely minute vacua which affect
the smallest particles so that that which binds
together the contiguous parts is throughout of
the same mintage ? Let me tell you something
which has just occurred to me and which I do
not offer as an absolute fact, but rather as a pass-
ing thought, still immature and calling for more
careful consideration. You may take of it what
you like; and judge the rest as you see fit. Some-
times when I have observed how fire winds its
way in between the most minute particles of
this or that metal and, even though these are
solidly cemented together, tears them apart and
separates them, and when I have observed that,
on removing the fire, these particles reunite with
the same tenacity as at first, without any loss^of
quantity in the case of gold and with little loss
THE TWO NEW SCIENCES
139
in the case of other metals, even though these
parts have been separated for a long while, I
have thought that the explanation might lie in
the fact that the extremely fine particles of fire,
penetrating the slender pores of the metal (too
small to admit even the finest particles of air or
of many other fluids), would fill the small inter-
vening vacua and would set free these small par-
ticles from the attraction which these same vac-
ua exert upon them and which prevents their
separation. Thus the particles are able to move
freely so that the mass becomes fluid and re-
mains so as long as the particles of fire remain
inside; but if they depart and leave the former
vacua then the original attraction returns and
the parts are again cemented together.
In reply to the question raised by Simplicio,
one may say that although each particular vacu-
um is exceedingly minute and therefore easily
overcome, yet their number is so extraordina-
rily great that their combined resistance is, so to
speak, multipled almost without limit. The na-
ture and the amount of force which results from
adding together in immense number of small
forces is clearly illustrated by the fact that a
weight of millions of pounds, suspended by great
cables, is overcome and lifted, when the south
wind carries innumerable atoms of water, sus-
pended in thin mist, which moving through the
air penetrate between the fibres of the tense
ropes in spite of the tremendous force of the
hanging weight. When these particles enter the
narrow pores they swell the ropes, thereby short-
en them, and perforce lift the heavy mass.
SAGR. There can be no doubt that any resist-
ance, so long as it is not infinite, may be over-
come by a multitude of minute forces. Thus a
vast number of ants might carry ashore a ship
laden with grain. And since experience shows us
daily that one ant can easily carry one grain, it
is clear that the number of grains in the ship is
not infinite, but falls below a certain limit. If
you take another number four or six times as
great, and if you set to work a corresponding
number of ants they will carry the grain ashore
and the boat also. It is true that this will call for
a prodigious number of ants, but in my opinion
this is precisely the case with the vacua which
bind together the least particles of a metal.
SALV. But even if this demanded an infinite
number would you still think it impossible ?
SAGR. Not if the mass of metal were infinite;
otherwise. . . .
SALV. Otherwise what ? Now since we have
arrived at paradoxes let us see if we cannot prove
that within a finite extent it is possible to dis-
cover an infinite number of vacua. At the same
time we shall at least reach a solution of the
most remarkable of all that list of problems which
Aristotle himself calls wonderful; I refer to his
Questions in Mechanics. This solution may be no
less clear and conclusive than that which he him-
self gives and quite different also from that so
cleverly expounded by the most learned Mon-
signor di Guevara.
First it is necessary to consider a proposition,
not treated by others, but upon which depends
the solution of the problem and from which, if I
mistake not, we shall -derive other new and re-
markable facts. For the sake of clearness let us
draw an accurate figure. About G as a centre
describe an equiangular and equilateral polygon
of any number of sides, say the hexagon ABC-
DEF. Similar to this and concentric with it, de-
scribe another smaller one which we shall call
HIKLMN. Prolong the side AB, of the larger
hexagon, indefinitely toward S\ in like manner
prolong the corresponding side HI of the small-
er hexagon, in the same direction, so that the
line HT is parallel to AS; and through the cen-
tre draw the line GV parallel to the other two.
This done, imagine the larger polygon to roll
upon the line AS, carrying with it the smaller
polygon. It is evident that, if the point B, the
end of the side AB, remains fixed at the begin-
ning of the rotation, the point A will rise and
the point C will fall describing the arc CQ until
the side BC coincides with the line BQ> equal to
BC. But during this rotation the point 7, on the
smaller polygon, will rise above the line IT be-
cause IB is oblique to AS', and it will not again
return to the line IT until the point C shall have
reached the position Q. The point /, having de-
scribed the arc 7O above the line HT, will reach
the position Oat the same time the side IK as-
sumes the position OP; but in the meantime the
centre G has traversed a path above GV and
does not return to it until it has completed the
arc GC. This step having been taken, the larger
polygon has been brought to rest with its side
BC coinciding with the line BQ while the side
IK of the smaller polygon has been made to co-
incide with the line OP, having passed over the
portion 7O without touching it; also the centre
G will have reached the position C after having
traversed all its course above the parallel line
GV. And finally the entire figure will assume a
position similar to the first, so that if we con-
tinue the rotation and come to the next step,
the side DC of the larger polygon will coincide
with the portion QX and the side KL of the
smaller polygon, having first skipped the arc
140
GALILEO GALILEI
Y Z
Fig- 5
Py, will fall on YZ, while the centre still keep-
ing above the line GV will return to it at R after
having jumped the interval CR. At the end of
one complete rotation the larger polygon will
have traced upon the line AS, without break,
six lines together equal to its perimeter; the
lesser polygon will likewise have imprinted six
lines equal to its perimeter, but separated by
the interposition of five arcs, whose chords rep-
resent the parts of HT not touched by the poly-
gon: the centre G never reaches the line GFex-
cept at six points. From this it is clear that the
space traversed by the smaller polygon is almost
equal to that traversed by the larger, that is, the
line //Tapproximates the line AS, differing from
it only by the length of one chord of one of these
arcs, provided we understand the line HT to in-
clude the five skipped arcs.
Now this exposition which I have given in the
case of these hexagons must be understood to be
applicable to all other polygons, whatever the
number of sides, provided only they are similar,
concentric, and rigidly connected, so that when
the greater one rotates the lesser will also turn
however small it may be. You must also under-
stand that the lines described by these two are
nearly equal provided we include in the space
traversed by the smaller one the intervals which
are not touched by any part of the perimeter of
this smaller polygon.
Let a large polygon of, say, one thousand sides
make one complete rotation and thus lay off a
line equal to its perimeter; at the same time the
small one will pass over an approximately equal
distance, made up of a thousand small portions
each equal to one of its sides, but interrupted
by a thousand spaces which, in contrast with
the portions that coincide with the sides of the
polygon, we may call empty. So far the matter
is free from difficulty or doubt.
But now suppose that about any centre, say
Ay we describe two concentric and rigidly con-
nected circles; and suppose that from the points
Cand B, on their radii, there are drawn the tan-
gents C£and BFand that through the centre A
the line AD is drawn parallel to them, then if
the large circle makes one complete rotation
along the line BF, equal not only to its circum-
ference but also to the other two lines CE and
AD, tell me what the smaller circle will do and
also what the centre will do. As to the centre it
will certainly traverse and touch the entire line
AD while the circumference of the smaller cir-
cle will have measured off by its points of con-
tact the entire line CE, just as was done by the
above mentioned polygons. The only difference
is that the line HT was not at every point in
contact with the perimeter of the smaller poly-
gon, but there were left untouched as many va-
cant spaces as there were spaces coinciding with
the sides. But here in the case of the circles the
circumference of the smaller one never leaves
the line CE, so that no part of the latter is left
untouched, nor is there ever a time when some
point on the circle is not in contact with the
straight line. How now can the smaller circle
traverse a length greater than its circumference
unless it go by jumps ?
THE TWO NEW SCIENCES
141
SAGR. It seems to me that one may say that
just as the centre of the circle, by itself, carried
along the line AD is constantly in contact with
it, although it is only a single point, so the points
on the circumference of the smaller circle, car-
ried along by the motion of the larger circle,
would slide over some small parts of the line CE.
SALV. There are two reasons why this cannot
happen. First because there is no ground for
thinking that one point of contact, such as that
at C, rather than another, should slip over cer-
tain portions of the line CE. But if such slidings
along CE did occur they would be infinite in
number since the points of contact (being mere
points) are infinite in number: an infinite num-
ber of finite slips will however make an infinite-
ly long line, while as a matter of fact the line
CEis finite. The other reason is that as the greater
circle, in its rotation, changes its point of con-
tact continuously the lesser circle must do the
same because B is the only point from which a
straight line can be drawn to A and pass through
G. Accordingly the small circle must change its
point of contact whenever the large one changes :
no point of the small circle touches the straight
line CE in more than one point. Not only so,
but even in the rotation of the polygons there
was no point on the perimeter of the smaller
which coincided with more than one point on
the line traversed by that perimeter; this is at
once clear when you remember that the line IK
is parallel to EC and that therefore IK will re-
main above /Pun til EC coincides with BQ, and
that IK will not lie upon IP except at the very
instant when EC occupies the position BQ; at
this instant the entire line IK coincides with OP
and immediately afterwards rises above it.
SAGR. This is a very intricate matter. I see no
solution. Pray explain it to us.
SALV. Let us return to the consideration of
the above mentioned polygons whose behavior
we already understand. Now in the case of poly-
gons with i ooooo sides, the line traversed by
the perimeter of the greater, i.e., the line laid
down by its i ooooo sides one after another, is
equal to the line traced out by the i ooooo sides
of the smaller, provided we include the i ooooo
vacant spaces interspersed. So in the case of the
circles, polygons having an infinitude of sides,
the line traversed by the continuously distribu-
ted infinitude of sides is in the greater circle
equal to the line laid down by the infinitude of
sides in the smaller circle but with the exception
that these latter alternate with empty spaces;
and since the sides are not finite in number, but
infinite, so also are the intervening empty spaces
not finite but infinite. The line traversed by the
larger circle consists^ then of an infinite number
of points which completely fill it; while that
which is traced by the smaller circle consists of
an infinite number of points which leave empty
spaces and only partly fill the line. And here I
wish you to observe that after dividing and re-
solving a line into a finite number of parts, that
is, into a number which can be counted, it is not
possible to arrange them again into a greater
length than that which they occupied when they
formed a continuum and were connected with-
out the interposition of as many empty spaces.
But if we consider the line resolved into an in-
finite number of infinitely small and indivisible
parts, we shall be able to conceive the line ex-
tended indefinitely by the interposition, not of
a finite, but of an infinite number of infinitely
small indivisible empty spaces.
Now this which has been said concerning sim-
ple lines must be understood to hold also in the
case of surfaces and solid bodies, it being as-
sumed that they are made up of an infinite, not
a finite, number of atoms. Such a body once di-
vided into a finite number of parts it is impos-
sible to reassemble them so as to occupy more
space than before unless we interpose a finite
number of empty spaces, that is to say, spaces
free from the substance of which the solid is
made. But if we imagine the body, by some ex-
treme and final analysis, resolved into its pri-
mary elements, infinite in number, then we
shall be able to think of them as indefinitely ex-
tended in space, not by the interposition of a
finite, but of an infinite number of empty spaces.
Thus one can easily imagine a small ball of gold
expanded into a very large space without the
introduction of a finite number of empty spaces,
always provided the gold is made up of an in-
finite number of indivisible parts.
SIMP. It seems to me that you are travelling
along toward those vacua advocated by a cer-
tain ancient philosopher.
SALV. But you have failed to add, "who denied
Divine Providence," an inapt remark made on
a similar occasion by a certain antagonist of our
Academician.
SIMP. I noticed, and not without indignation,
the rancor of this ill-natured opponent; further
references to these affairs I omit, not only as a
matter of good form, but also because I know
how unpleasant they are to the good tempered
and well ordered mind of one so religious and
pious, so orthodox and God-fearing as you.
But to return to our subject, your previous
discourse leaves with me many difficulties which
142
GALILEO GALILEI
I am unable to solve. First among these is that,
if the circumferences of th« two circles are equal
to the two straight lines, CE and #F, the latter
considered as a continuum, the former as inter-
rupted with an infinity of empty points, I do
not see how it is possible to say that the line
AD described by the centre, and made up of
an infinity of points, is equal to this centre
which is a single point. Besides, this building
up of lines out of points, divisibles out of in-
divisibles, and finites out of infinites, offers me
an obstacle difficult to avoid; and the necessity
of introducing a vacuum, so conclusively re-
futed by Aristotle, presents the same difficulty.
SALV. These difficulties are real; and they are
not the only ones. But let us remember that
we are dealing with infinities and indivisibles
both of which transcend our finite understand-
ing, the former on account of their magnitude,
the latter because of their smallness. In spite of
this, men cannot refrain from discussing them,
even though it must be done in a roundabout
way.
Therefore I also should like to take the liberty
to present some of my ideas which, though not
necessarily convincing, would, on account of
their novelty, at least, prove somewhat start-
ling. But such a diversion might perhaps carry
us too far away from the subject under discus-
sion and might therefore appear to you inop-
portune and not very pleasing.
SACK. Pray let us enjoy the advantages and
privileges which come from conversation be-
tween friends, especially upon subjects freely
chosen and not forced upon us, a matter vastly
different from dealing with dead books which
give rise to many doubts but remove none.
Share with us, therefore, the thoughts which
our discussion has suggested to you; for since
we are free from urgent business there will be
abundant time to pursue the topics already
mentioned; and in particular the objections
raised by Simplicio ought not in any wise to be
neglected.
SALV. Granted, since you so desire. The first
question was, How can a single point be equal
to a line? Since I cannot do more at present I
shall attempt to remove, or at least dimmish,
one improbability by introducing a similar or a
greater one, just as sometimes a wonder is di-
minished by a miracle.1
And this I shall do by showing you two equal
surfaces, together with two equal solids located
upon these same surfaces as bases, all four of
which diminish continuously and uniformly in
lCf. p. 143 below. — TRANS.
such a way that their remainders always pre-
serve equality among themselves, and finally
both the surfaces and the solids terminate their
previous constant equality by degenerating, the
one solid and the one surface into a very long
line, the other solid and the other surface into
a single point; that is, the latter to one point,
the former to an infinite number of points.
SAGR. This proposition appears to me won-
derful, indeed; but let us hear the explanation
and demonstration.
SALV. Since the proof is purely geometrical
we shall need a figure. Let AFB be a semicircle
with centre at C; about it describe the rec-
tangle ADEB and from the centre draw the
straight lines CD and CE to the points D and
E. Imagine the radius CF to be drawn per-
pendicular to either of the lines AB or DE,
and the entire figure to rotate about this ra-
dius as an axis. It is clear that the rectangle
ADEB will thus describe a cylinder, the semi-
circle AFB a hemisphere, and the triangle
CDEj a cone. Next let us remove the hemi-
sphere but leave the cone and the rest of the
cylinder, which, on account of its shape, we
will call a "bowl." First we shall prove that
the bowl and the cone are equal; then we shall
show that a plane drawn parallel to the circle
which forms the base of the bowl and which
has the line DE for diameter and /; for a centre
—a plane whose trace is GN— cuts the bowl in
the points (7, /, O, JV, and the cone in the points
//, L, so that the part of the cone indicated by
CHL is always equal to the part of the bowl
whose profile is represented by the triangles
GAI and BON. Besides this we shall prove that
the base of the cone, i.e., the circle whose diam-
eter is HLt is equal to the circular surface which
A C B
\!
D
N
F
Fig. 6
forms the base of this portion of the bowl, or as
one might say, equal to a ribbon whose width is
GL (Note by the way the nature of mathemati-
cal definitions which consist merely in the im-
position of names or, if you prefer, abbrevia-
tions of speech established and introduced in
order to avoid the tedious drudgery which you
and I now experience simply because we have
THE TWO NEW SCIENCES
not agreed to call this surface a "circular band"
and that sharp solid portion of the bowl a
"round razor.") Now call them by what name
you please, it suffices to understand that the
plane, drawn at any height whatever, so long
as it is parallel to the base, i.e., to the circle
whose diameter is DE, always cuts the two sol-
ids so that the portion CHL of the cone is equal
to the upper portion of the bowl; likewise the
two areas which are the bases of these solids,
namely the band and the circle HL, are also
equal. Here we have the miracle mentioned
above; as the cutting plane approaches the line
AB the portions of the solids cut off are always
equal, so also the areas of their bases. And as the
cutting plane comes near the top, the two sol-
ids (always equal) as well as their bases (areas
which are also equal) finally vanish, one pair of
them degenerating into the circumference of a
circle, the other into a single point, namely, the
upper edge of the bowl and the apex of the
cone. Now, since as these solids dimmish equal-
ity is maintained between them up to the very
last, we are justified in saying that, at the ex-
treme and final end of this diminution, they
are still equal and that one is not infinitely
greater than the other. It appears therefore that
we may equate the circumference of a large cir-
cle to a single point. And this which is true of
the solids is true also of the surfaces which form
their bases; for these also preserve equality be-
tween themselves throughout their diminution
and in the end vanish, the one into the circum-
ference of a circle, the other into a single point.
Shall we not then call them equal seeing that
they are the last traces and remnants of equal
magnitudes ? Note also that, even if these ves-
sels were large enough to contain immense ce-
lestial hemispheres, both their upper edges and
the apexes of the cones therein contained would
always remain equal and would vanish, the for-
mer into circles having the dimensions of the
largest celestial orbits, the latter into single
points. Hence in conformity with the preced-
ing we may say that all circumferences of cir-
cles, however different, are equal to each other,
and are each equal to a single point.
SAGR. This presentation strikes me as so clev-
er and novel that, even if I were able, I would
not be willing to oppose it; for to deface so
beautiful a structure by a blunt pedantic at-
tack would be nothing short of sinful. But for
our complete satisfaction pray give us this geo-
metrical proof that there is always equality be-
tween these solids and between their bases; for
it cannot, I think, fail to be very ingenious, see-
ing how subtle is the philosophical argument
based upon this result.
SALV. The demonstration is both short and
easy. Referring to the preceding figure, since
/PC is a right angle the square of the radius 1C
is equal to the sum of the squares on the two
sides /P, PC; but the radius 1C is equal to AC
and also to GP, while CP is equal to PH. Hence
the square of the line GP is equal to the sum
of the squares of IP and PH, or multiplying
through by 4, we have the square of the diame-
ter GN equal to the sum of the squares on IO
and HL. And, since the areas of circles are to
each other as the squares of their diameters, it
follows that the area of the circle whose diame-
ter is GN is equal to the sum of the areas of
circles having diameters 10 and HL, so that if
we remove the common area of the circle hav-
ing 10 for diameter the remaining area of the
circle GN will be equal to the area of the circle
whose diameter is HL. So much for the first
part. As for the other part, we leave its demon-
stration for the present, partly because those
who wish to follow it will find it in the twelfth
proposition of the second book of De centra gra-
vitatis solidorum by the Archimedes of our age,
Luca Valerio, who made use of it for a different
object, and partly because, for our purpose, it
suffices to have seen that the above-mentioned
surfaces are always equal and that, as they keep
on diminishing uniformly, they degenerate, the
one into a single point, the other into the cir-
cumference of a circle larger than any assign-
able; in this fact lies our miracle.
SAGR. The demonstration is ingenious and
the inferences drawn from it are remarkable.
And now let us hear something concerning the
other difficulty raised by Simplicio, if you have
anything special to say, which, however, seems
to me hardly possible, since the matter has al-
ready been so thoroughly discussed.
SALV. But I do have something special to
say, and will first of all repeat what I said a lit-
tle while ago, namely, that infinity and indivisi-
bility are in their very nature incomprehensi-
ble to us; imagine then what they are when
combined. Yet if we wish to build up a line out
of indivisible points, we must take an infinite
number of them, and are, therefore, bound to
understand both the infinite and the indivisible
at the same time. Many ideas have passed
through my mind concerning this subject, some
of which, possibly the more important, I may
not be able to recall on the spur of the moment;
but in the course of our discussion it may hap-
pen that I shall awaken in you, and especially
144
GALILEO GALILEI
in Simplicio, objections and difficulties which
in turn will bring to memory that which, with-
out such stimulus, would have lain dormant in
my mind. Allow me therefore the customary
liberty of introducing some of our human fan-
cies, for indeed we may so call them in compari-
son with supernatural truth which furnishes the
one true and safe recourse for decision in our
discussions and which is an infallible guide in
the dark and dubious paths of thought.
One of the main objections urged against
this building up of continuous quantities out
of indivisible quantities is that the addition of
one indivisible to another cannot produce a di-
visible, for if this were so it would render the
indivisible divisible. Thus if two indivisibles,
say two points, can be united to form a quan-
tity, say a divisible line, then an even more
divisible line might be formed by the union
of three, five, seven, or any other odd number
of points. Since however these lines can be cut
^nto two equal parts, it becomes possible to cut
the indivisible which lies exactly in the middle
of the line. In answer to this and other objec-
tions of the same type we reply that a divisible
magnitude cannot be constructed out of two
or ten or a hundred or a thousand indivisibles,
but requires an infinite number of them.
SIMP. Here a difficulty presents itself which
appears to me insoluble. Since it is clear that we
may have one line greater than another, each
containing an infinite number of points, we are
forced to admit that, within one and the same
class, we may have something greater than in-
finity, because the infinity of points in the long
line is greater than the infinity of points in the
short line. This assigning to an infinite quantity
a value greater than infinity is quite beyond my
comprehension.
SALV. This is one of the difficulties which
arise when we attempt, with our finite minds,
to discuss the infinite, assigning to it those prop-
erties which we give to the finite and limited;
but this I think is wrong, for we cannot speak
of infinite quantities as being the one greater
or less than or equal to another. To prove this
I have in mind an argument which, for the sake
of clearness, I shall put in the form of questions
to Simplicio who raised this difficulty.
I take it for granted that you know which of
the numbers are squares and which are not.
SIMP. I am quite aware that a squared num-
ber is one which results from the multiplication
of another number by itself; thus 4, 9, etc., are
squared numbers which come from multiply-
ing 2, 3, etc., by themselves.
SALV, Very well; and you also know that just
as the products are called squares so the factors
are called sides or roots; while on the other hand
those numbers which do not consist of two equal
factors are not squares. Therefore if I assert that
all numbers, including both squares and non-
squares, are more than the squares alone, I shall
speak the truth, shall I not?
SIMP. Most certainly.
SALV. If I should ask further how many
squares there are one might reply truly that
there are as many as the corresponding number
of roots, since every square has its own root and
every root its own square, while no square has
more than one root and no root more than one
square.
SIMP. Precisely so.
SALV. But if I inquire how many roots there
are, it cannot be denied that there are as many
as there are numbers because every number is a
root of some square. This being granted we
must say that there are as many squares as there
are numbers because they are just as numerous
as their roots, and all the numbers are roots. Yet
at the outset we said there are many more num-
bers than squares, since the larger portion of
them are not squares. Not only so, but the pro-
portionate number of squares diminishes as we
pass to larger numbers. Thus up to 100 we have
10 squares, that is, the squares constitute i/io
part of all the numbers; up to 10000, we find
only i/ioo part to be squares; and up to a mil-
lion only i/iooo part; on the other hand in an
infinite number, if one could conceive of such
a thing, he would be forced to admit that there
are as many squares as there are numbers all
taken together.
SAGR. What then must one conclude under
these circumstances ?
SALV. So far as I see we can only infer that the
totality of all numbers is infinite, that the num-
ber of squares is infinite, and that the number
of their roots is infinite; neither is the number of
squares less than the totality of all numbers, nor
the latter greater than the former; and finally
the attributes "equal," "greater," and "less,*'
are not applicable to infinite, but only to finite,
quantities. When therefore Simplicio intro-
duces several lines of different lengths and asks
me how it is possible that the longer ones do
not contain more points than the shorter, I an-
swer him that one line does not contain more
or less or just as many points as another, but
that each line contains an infinite number. Or
if I had replied to him that the points in one
line were equal in number to the squares; in
THE TWO NEW SCIENCES
'45
another, greater than the totality of numbers;
and in the little one, as many as the number of
cubes, might I not, indeed, have satisfied him
by thus placing more points in one line than in
another and yet maintaining an infinite num-
ber in each ? So much for the first difficulty.
SAGR. Pray stop a moment and let me add to
what has already been said an idea which just
occurs to me. If the preceding be true, it seems
to me impossible to say either that one infinite
number is greater than another or even that it
is greater than a finite number, because if the
infinite number were greater than, say, a mil-
lion it would follow that on passing from the
million to higher and higher numbers we would
be approaching the infinite; but this is not so;
on the contrary, the larger the number to which
we pass, the more we recede from infinity, be-
cause the greater the numbers the fewer are the
squares contained in them; but the squares in
infinity cannot be less than the totality of all
the numbers, as we have just agreed; hence the
approach to greater and greater numbers
means a departure from infinity.
SALV. And thus from your ingenious argu-
ment we are led to conclude that the attributes
"larger," "smaller," and "equal" have no place
either in comparing infinite quantities with
each other or in comparing infinite with finite
quantities.
I pass now to another consideration. Since
lines and all continuous quantities are divisible
into parts which are themselves divisible with-
out end, I do not see how it is possible to avoid
the conclusion that these lines are built up of an
infinite number of indivisible quantities because
a division and a subdivision which can be car-
ried on indefinitely presupposes that the parts
are infinite in number, otherwise the subdivi-
sion would reach an end; and if the parts are
infinite in number, we must conclude that they
are not finite in size, because an infinite num-
ber of finite quantities would give an infinite
magnitude. And thus we have a continuous
quantity built up of an infinite number of in-
divisibles.
SIMP. But if we can carry on indefinitely the
division into finite parts what necessity is there
then for the introduction of non-finite parts?
SALV. The very fact that one is able to con-
tinue, without end, the division into finite parts
makes it necessary to regard the quantity as
composed of an infinite number of immeasur-
ably small elements. Now in order to settle this
matter I shall ask you to tell me whether, in
your opinion, a continuum is made up of a finite
or of an infinite number of finite parts.
SIMP. My answer is that their number is both
infinite and finite; potentially infinite but act-
ually finite; that is to say, potentially infinite
before division and actually finite after division ;
because parts cannot be said to exist in a body
which is not yet divided or at least marked out;
if this is not done we say that they exist poten-
tially.
SALV. So that a line which is, for instance,
twenty spans long is not said to contain actually
twenty lines each one span in length except
after division into twenty equal parts; before
division it is said to contain them only poten-
tially. Suppose the facts are as you say; tell me
then whether, when the division is once made,
the size of the original quantity is thereby in-
creased, diminished, or unaffected.
SIMP. It neither increases nor diminishes.
SALV. That is my opinion also. Therefore the
finite parts in a continuum, whether actually or
potentially present, do not make the quantity
either larger or smaller; but it is perfectly clear
that, if the number of finite parts actually con-
tained in the whole is infinite in number, they
will make the magnitude infinite. Hence the
number of finite parts, although existing only
potentially, cannot be infinite unless the mag-
nitude containing them be infinite; and con-
versely if the magnitude is finite it cannot con-
tain an infinite number of finite parts either
actually or potentially.
SAGR. How then is it possible to divide a con-
tinuum without limit into parts which are them-
selves always capable of subdivision ?
SALV. This distinction of yours between
actual and potential appears to render easy by
one method what would be impossible by an-
other. But I shall endeavor to reconcile these
matters in another way; and as to the query
whether the finite parts of a limited continuum
are finite or infinite in number I will, contrary
to the opinion of Simplicio, answer that they
are neither finite nor infinite.
SIMP. This answer would never have occurred
to me since I did not think that there existed
any intermediate step between the finite and
the infinite, so that the classification or distinc-
tion which assumes that a thing must be either
finite or infinite is faulty and defective.
SALV. So it seems to me. And if we consider
discrete quantities I think there is, between
finite and infinite quantities, a third intermed-
iate term which corresponds to every assigned
number; so that if asked, as in the present case,
whether the finite parts of a continuum are finite
146
GALILEO GALILEI
or infinite in number the best reply is that they
are neither finite nor infinite but correspond to
every assigned number. In order that this may
be possible, it is necessary that those parts
should not be included within a limited num-
ber, for in that case they would not correspond
to a number which is greater; nor can they be
infinite in number since no assigned number is
infinite; and thus at the pleasure of the ques-
tioner we may, to any given line, assign a hun-
dred finite parts, a thousand, a hundred thou-
sand, or indeed any number we may please so
long as it be not infinite. I grant, therefore, to
the philosophers, that the continuum contains
as many finite parts as they please and I con-
cede also that it contains them, either actually
or potentially, as they may like; but I must add
that just as a line ten fathoms in length con-
tains ten lines each of one fathom and forty lines
each of one cubit and eighty lines each of half a
cubit, etc., so it contains an infinite number of
points; call them actual or potential, as you like,
for as to this detail, Sirnplicio, I defer to your
opinion and to your judgment.
SIMP. I cannot help admiring your discussion;
but I fear that this parallelism between the
points and the finite parts contained in a line
will not prove satisfactory, and that you will
not find it so easy to divide a given line into an
infinite number of points as the philosophers do
to cut it into ten fathoms or forty cubits; not
only so, but such a division is quite impossible
to realize in practice, so that this will be one of
those potentialities which cannot be reduced
to actuality.
SALV. The fact that something can be done
only with effort or diligence or with great ex-
penditure of time does not render it impossible;
for I think that you yourself could not easily
divide a line into a thousand parts, and much
less if the number of parts were 937 or any other
large prime number. But if I were to accom-
plish this division which you deem impossible as
readily as another person would divide the line
into forty parts would you then be more will-
ing, in our discussion, to concede the possibility
of such a division ?
SIMP. In general I enjoy greatly your meth-
od; and replying to your query, I answer that
it would be more than sufficient if it prove not
more difficult to resolve a line into points than
to divide it into a thousand parts.
SALV. I will now say something which may
perhaps astonish you; it refers to the possibility
of dividing a line into its infinitely small ele-
ments by following the same order which one
employs in dividing the same line into forty,
sixty, or a hundred parts, that is, by dividing
it into two, four, etc. He who thinks that, by
following this method, he can reach an infinite
number of points is greatly mistaken; for if this
process were followed to eternity there would
still remain finite parts which were undivided.
Indeed by such a method one is very far from
reaching the goal of indivisibility; on the con-
trary, he recedes from it and while he thinks
that, by continuing this division and by multi-
plying the multitude of parts, he will approach
infinity, he is, in my opinion, getting farther
and farther away from it. My reason is this. In
the preceding discussion we concluded that, in
an infinite number, it is necessary that the
squares and cubes should be as numerous as the
totality of the natural numbers, because both
of these are as numerous as their roots which
constitute the totality of the natural numbers.
Next we saw that the larger the numbers taken
the more sparsely distributed were the squares,
and still more sparsely the cubes; therefore it is
clear that the larger the numbers to which we
pass the farther we recede from the infinite
number; hence it follows that, since this process
carries us farther and farther from the end
sought, if on turning back we shall find that any
number can be said to be infinite, it must be
unity. Here indeed are satisfied all those con-
ditions which are requisite for an infinite num-
ber; I mean that unity contains in itself as many
squares as there are cubes and natural numbers.
SIMP. I do not quite grasp the meaning of
this.
SALV. There is no difficulty in the matter
because unity is at once a square, a cube, a
square of a square and all the other powers, nor
is there any essential peculiarity in squares or
cubes which does not belong to unity; as, for
example, the property of two square numbers
that they have between them a mean propor-
tional; take any square number you please as
the first term and unity for the other, then you
will always find a number which is a mean pro-
portional. Consider the two square numbers, 9
and 4; then 3 is the mean proportional between
9 and i ; while 2 is a mean proportional between
4 and i ; between 9 and 4 we have 6 as a mean
proportional. A property of cubes is that they
must have between them two mean propor-
tional numbers; take 8 and 27; between them
lie 12 and 18; while between i and 8 we have
2 and 4 intervening; and between i and 27
there lie 3 and 9. Therefore we conclude that
unity is the only infinite number. These are
THE TWO NEW SCIENCES
some of the marvels which our imagination can-
not grasp and which should warn us against the
serious error of those who attempt to discuss
the infinite by assigning to it the same proper-
ties which we employ for the finite, the natures
of the two having nothing in common.
With regard to this subject I must tell you of
a remarkable property which just now occurs
to me and which will explain the vast alteration
and change of character which a finite quan-
tity would undergo in passing to infinity. Let
us draw the straight line AB of arbitrary length
and let the point C divide it into two unequal
parts; then I say that, if pairs of lines be drawn,
one from each of the terminal points A and B,
and if the ratio between the lengths of these
lines is the same as that between AC and CB,
their points of intersection will all lie upon the
circumference of one and the same circle. Thus,
for example, AL and BL drawn from A and B,
meeting at the point L, bearing to one another
the same ratio as AC to EC, and the pair AK
and BK meeting at K also bearing to one an-
other the same ratio, and likewise the pairs Al,
Bl, AH, BH, AG, EG, AF, BF, AE, BE, have
their points of intersection L, K, I, H, G, F, E,
all lying upon the circumference of one and the
same circle. Accordingly if we imagine the point
C to move continuously in such a manner that
the lines drawn from it to the fixed terminal
points, A and B, always maintain the same ra-
tio between their lengths as exists between the
original parts, AC and CB, then the point C
will, as I shall presently prove, describe a circle.
And the circle thus described will increase in
size without limit as the point C approaches the
middle point which we may call O; but it will
diminish in size as C approaches the end B. So
that the infinite number of points located in
the line OB will, if the motion be as explained
above, describe circles of every size, some
smaller than the pupil of the eye of a flea, others
larger than the celestial equator. Now if we
move any of the points lying between the two
ends O and B they will all describe circles, those
nearest O, immense circles; but if we move the
point O itself, and continue to move it accord-
ing to the aforesaid law, namely, that the lines
drawn from O to the terminal points, A and B,
maintain the same ratio as the original lines AO
and OB, what kind of a line will be produced ?
A circle will be drawn larger than the largest of
the others, a circle which is therefore infinite.
But from the point 0 a straight line will also be
drawn perpendicular to BA and extending to
infinity without ever turning, as did the others,
to join its last end with its first; for the point C,
with its limited motion, having described the
upper semicircle, CHE, proceeds to describe
the lower semicircle EMC, thus returning to
the starting point. But the point O having
started to describe its circle, as did all the other
points in the line AB, (for the points in the
other portion 0 A describe their circles also, the
largest being those nearest the point O) is un-
able to return to its starting point because
the circle it describes, being the largest of
all, is infinite ; in fact, it describes an infinite
straight line as circumference of its infinite
circle. Think now what a difference there is
between a finite and an infinite circle since
the latter changes character in such a man-
ner that it loses not only its existence but
also its possibility of existence; indeed, we
already clearly understand that there can
be no such thing as an infinite circle; simi-
larly there can be no infinite sphere, no in-
finite body, and no infinite surface of any
shape. Now what shall we say concerning this
metamorphosis in the transition from finite to
infinite? And why should we feel greater re-
pugnance, seeing that, in our search after the
infinite among numbers we found it in unity?
Having broken up a solid into many parts, hav-
ing reduced it to the finest of powder and hav-
ing resolved it into its infinitely small indivisi-
ble atoms why may we not say that this solid
has been reduced to a single continuum perhaps
a fluid like water or mercury or even a liquified
metal ? And do we not see stones melt into glass
and the glass itself under strong heat become
more fluid than water?
SAGR. Are we then to believe that substances
become fluid in virtue of being resolved into
their infinitely small indivisible components?
SALV. I am not able to find any better means
of accounting for certain phenomena of which
the following is one. When I take a hard sub-
stance such as stone or metal and when I reduce
148
GALILEO GALILEI
it by means of a hammer or fine file to the most
minute and impalpable powder, it is clear that
its finest particles, although when taken one by
one are, on account of their smallness, imper-
ceptible to our sight and touch, are nevertheless
finite in size, possess shape, and capability of be-
ing counted. It is also true that when once
heaped up they remain in a heap; and if an
excavation be made within limits the cavity
will remain and the surrounding particles will
not rush in to fill it; if shaken the particles come
to rest immediately after the external disturb-
ing agent is removed; the same effects are ob-
served in all piles of larger and larger particles,
of any shape, even if spherical, as is the case
with piles of millet, wheat, lead shot, and every
other material. But if we attempt to discover
such properties in water we do not find them;
for when once heaped up it immediately flattens
out unless held up by some vessel or other ex-
ternal retaining body; when hollowed out it
quickly rushes in to fill the cavity; and when
disturbed it fluctuates fora long time and sends
out its waves through great distances.
Seeing that water has less firmness than the
finest of powder, in fact has no consistence
whatever, we may, it seems to me, very reason-
ably conclude that the smallest particles into
which it can be resolved are quite different
from finite and divisible particles; indeed the
only difference I am able to discover is that the
former are indivisible. The exquisite transpar-
ency of water also favors this view; for the most
transparent crystal when broken and ground
and reduced to powder loses its transparency;
the finer the grinding the greater the loss; but
in the case of water where the attrition is of the
highest degree we have extreme transparency.
Gold and silver when pulverized with acids
more finely than is possible with any file still
remain powders, and do not become fluids until
the finest particles of fire or of the rays of the
sun dissolve them, as I think, into their ulti-
mate, indivisible, and infinitely small compon-
ents.
SAGR. This phenomenon of light which you
mention is one which I have many times re-
marked with astonishment. I have, for instance,
seen lead melted instantly by means of a con-
cave mirror only three hands in diameter.
Hence I think that if the mirror were very
large, well-polished and of a parabolic figure, it
would just as readily and quickly melt any other
metal, seeing that the small mirror, which was
not well polished and had only a spherical shape,
was able so energetically to melt lead and burn
every combustible substance. Such effects as
these render credible to me the marvels accom-
plished by the mirrors of Archimedes.
SALV. Speaking of the effects produced by
the mirrors of Archimedes, it was his own books
(which I had already read and studied with in-
finite astonishment) that rendered credible to
me all the miracles described by various writers.
And if any doubt had remained, the book which
Father Buonaventura Cavalieri1 has recently
published on the subject of the burning glass
and which I have read with admiration would
have removed the last difficulty.
SAGR. I also have seen this treatise and have
read it with pleasure and astonishment; and
knowing the author I was confirmed in the
opinion which I had already formed of him,
that he was destined to become one of the lead-
ing mathematicians of our age. But now, with
regard to the surprising effect of solar rays in
melting metals, must we believe that such a
furious action is devoid of motion or that it is
accompanied by the most rapid of motions ?
SALV. We observe that other combustions
and resolutions are accompanied by motion, and
that, the most rapid; note the action of light-
ning and of powder as used in mines and pe-
tards; note also how the charcoal flame, mixed
as it is with heavy and impure vapours, in-
creases its power to liquify metals whenever
quickened by a pair of bellows. Hence I do not
understand how the action of light, although
very pure, can be devoid of motion and that of
the swiftest type.
SAGR. But of what kind and how great must
we consider this speed of light to be ? Is it in-
stantaneous or momentary or does it like other
motions require time? Can we not decide this
by experiment ?
SIMP. Everyday experience shows that the
propagation of light is instantaneous; for when
we see a piece of artillery fired, at great distance,
the flash reaches our eyes without lapse of time;
but the sound reaches the ear only after a no-
ticeable interval.
SAGR. Well, Simplicio, the only thing I am
able to infer from this familiar bit of experience
is that sound, in reaching our ear, travels more
slowly than light; it does not inform me whether
the coming of the light is instantaneous or
whether, although extremely rapid, it still oc-
1 One of the most active investigators among Galileo's
contemporaries; a Jesuit, first to introduce the use of log-
arithms into Italy and first to derive the expression for
the focal length of a lens having unequal radii of curva-
ture. TRANS.
THE TWO NEW SCIENCES
149
cupies time. An observation of this kind tells us
nothing more than one in which it is claimed
that "As soon as the sun reaches the horizon
its light reaches our eyes"; but who will assure
me that these rays had not reached this limit
earlier than they reached our vision ?
SALV. The small collusiveness of these and
other similar observations once led me to de-
vise a method by which one might accurately
ascertain whether illumination, i.e., the propa-
gation of light, is really instantaneous. The fact
that the speed of sound is as high as it is, assures
us that the motion of light cannot fail to be
extraordinarily swift. The experiment which I
devised was as follows:
Let each of two persons take a light con-
tained in a lantern, or other receptacle, such
that by the interposition of the hand, the one
can shut off or admit the light to the vision of
the other. Next let them stand opposite each
other at a distance of a few cubits and practice
until they acquire such skill in uncovering and
occulting their lights that the instant one sees
the light of his companion he will uncover his
own. After a few trials the response will be so
prompt that without sensible error the uncov-
ering of one light is immediately followed by
the uncovering of the other, so that as soon as
one exposes his light he will instantly see that
of the other. Having acquired skill at this short
distance let the two experimenters, equipped
as before, take up positions separated by a dis-
tance of two or three miles and let them per-
form the same experiment at night, noting care-
fully whether the exposures and occultations
occur in the same manner as at short distances;
if they do, we may safely conclude that the
propagation of light is instantaneous; but if
time is required at a distance of three miles
which, considering the going of one light and
the coming of the other, really amounts to six,
then the delay ought to be easily observable.
If the experiment is to be made at still greater
distances, say eight or ten miles, telescopes may
be employed, each observer adjusting one for
himself at the place where he is to make the
experiment at night; then although the lights
are not large and are therefore invisible to the
naked eye at so great a distance, they can read-
ily be covered and uncovered since by aid of
the telescopes, once adjusted and fixed, they
will become easily visible.
SAGR. This experiment strikes me as a clever
and reliable invention. But tell us what you
conclude from the results.
SALV. In fact I have tried the experiment
only at a short distance, less than a mile, from
which I have not been able to ascertain with cer-
tainty whether the appearance of the opposite
light was instantaneous or not; but if not in-
stantaneous it is extraordinarily rapid — I should
call it momentary; and for the present I should
compare it to motion which we see in the light-
ning flash between clouds eight or ten miles
distant from us. We see the beginning of this
light — I might say its head and source — located
at a particular place among the clouds; but it
immediately spreads to the surrounding ones,
which seems to be an argument that at least
some time is required for propagation; for if the
illumination were instantaneous and not grad-
ual, we should not be able to distinguish its
origin — its centre, so to speak — from its out-
lying portions. What a sea we are gradually
slipping into without knowing it! With vacua
and infinities and indivisibles and instantaneous
motions, shall we ever be able, even by means
of a thousand discussions, to reach dry land?
SAGR. Really these matters lie far beyond
our grasp. Just think; when we seek the infinite
among numbers we find it in unity; that which
is ever divisible is derived from indivisibles;
the vacuum is found inseparably connected
with the plenum; indeed the views commonly
held concerning the nature of these matters are
so reversed that even the circumference of a
circle turns out to be an infinite straight line, a
fact which, if my memory serves me correctly,
you, Salviati, were intending to demonstrate
geometrically. Please therefore proceed with-
out further digression.
SALV. I am at your service; but for the sake
of greater clearness let me first demonstrate the
following problem:
Given a straight line divided into unequal parts
which bear to each other any ratio whatever, to
describe a circle such that two straight lines drawn
from the ends of the given line to any point on the
circumference will bear to each other the same
ratio as the two parts of the given line, thus making
those lines which are drawn from the same termi-
nal points homologous.
Let AB represent the given straight line di-
vided into any two unequal parts by the point
C; the problem is to describe a circle such that
two straight lines drawn from the terminal
points, A and B, to any point on the circum-
ference will bear to each other the same ratio
as the part AC bears to BC, so that lines drawn
from the same terminal points are homologous.
About C as centre describe a circle having the
150
GALILEO GALILEI
shorter part CB of the given line, as radius.
Through A draw a straight line AD which shall
be tangent to the circle at D and indefinitely
prolonged toward E. Draw the radius CD
which will be perpendicular to AE. At B erect
a perpendicular to AB; this perpendicular will
intersect AE at some point since the angle at A
is acute; call this point of intersection E, and
from it draw a perpendicular to AE which will
intersect AB prolonged in F. Now I say the two
straight lines FE and PC are equal. For if we
join £ and C, we shall have two triangles, DEC
and BEC, in which the two sides of the one,
DE and EC, are equal to the two sides of the
other, BE and EC, both DE and EB being tan-
gents to the circle DB while the bases DC and
CB are likewise equal; hence the two angles,
DEC and BEC, will be equal. Now since the
angle BCE differs from a right angle by the
angle CEB, and the angle CEF also differs
from a right angle by the angle CED, and
since these differences are equal, it follows
that the angle FCE is equal to CEP; conse-
quently the sides FE and FC are equal. If we
describe a circle with F as centre and FE as
radius it will pass through the point C; let CEG
be such a circle. This is the circle sought, for if
we draw lines from the terminal points A and
B to any point on its circumference they will
bear to each other the same ratio as the two
portions AC and BC which meet at the point
C. This is manifest in the case of the two lines
AEand BE, meeting at the point E, because the
angle E of the triangle AEB is bisected by the
line CE, and therefore AC : CB = AE: BE. The
same may be proved of the two lines AG and
BG terminating in the point G. For since the
triangles APE and EFB are similar, we have
AF : FE^EF : FB, or AF : FC=CF: FB, and
dividendo AC : CF= CB : BF, or AC : FG =
CB : BF; also componendo we have both
AB : BG=CB : 5Fand AG : GB = CF:FB =
AE : EB = AC : BC. Q. E. D.
Take now any other point in the circum-
ference, say H, where the two lines AH
and BH intersect; in like manner we shall
have AC:CB = AH: HB. Prolong HB un-
til it meets the circumference at / and join
IF; and since we have already found that
AB :BG = CB : BFit follows that the rec-
tangle AB-BFis equal to the rectangle
CB-BG or IB-BH. Hence AB : BH =
'G IB : BF. But the angles at B are equal and
therefore AH:HB = IF: FB = EF : FB=*
AE : EB.
Besides, I may add, that it is impossible
for lines which maintain this same ratio and
which are drawn from the terminal points,
A and B, to meet at any point either inside
or outside the circle, CEG. For suppose this
were possible; let AL and BL be two such
lines intersecting at the point L outside the
circle : prolong LB till it meets the circumference
atMand)omMF.lfAL:BL=AC:BC=MF:
FB, then we shall have two triangles ALB and
MFB which have the sides about the two angles
proportional, the angles at the vertex, B, equal,
and the two remaining angles, FMB and LAB,
less than right angles (because the right angle at
M has for its base the entire diameter CG and
not merely a part BF: and the other angle at the
point A is acute because the line AL, the homolo-
gue of AC, is greater than BL, the homologue
of BC). From this it follows that the triangles
ABL and MBF are similar and therefore AB :
BL = MB:BF, making the rectangle AB-BF=
MB-BL; but it has been demonstrated that the
rectangle AB-BF is equal to CB BG; whence it
would follow that the rectangle MB-BL is equal
to the rectangle CB'BG which is impossible;
therefore the intersection cannot fall outside the
circle. And in like manner we can show that it
cannot fall inside; hence all these intersections
fall on the circumference.
But now it is time for us to go back and grant
the request of Simplicio by showing him that it
is not only not impossible to resolve a line into
an infinite number of points but that this is quite
as easy as to divide it into its finite parts. This
I will do under the following condition which
I am sure, Simplicio, you will not deny me,
namely, that you will not require me to sep-
arate the points, one from the other, and show
them to you, one by one, on this paper; for I
should be content that you, without separating
THE TWO NEW SCIENCES
the four or six parts of a line from one another,
should show me the marked divisions or at
most that you should fold them at angles form-
ing a square or a hexagon : for, then, I am certain
you would consider the division distinctly and
actually accomplished.
SIMP. I certainly should.
SALV. If now the change which takes place
when you bend a line at angles so as to form
now a square, now an octagon, now a polygon
of forty, a hundred or a thousand angles, is suf-
ficient to bring into actuality the four, eight,
forty, hundred, and thousand parts which, ac-
cording to you, existed at first only potentially
in the straight line, may I not say, with equal
right, that, when I have bent the straight line
into a polygon having an infinite number of
sides, /. £., into a circle, I have reduced to actu-
ality that infinite number of parts which you
claimed, while it was straight, were contained
in it only potentially? Nor can one deny that
the division into an infinite number of points is
just as truly accomplished as the one into four
parts when the square is formed or into a thou-
sand parts when the millagon is formed; for in
such a division the same conditions are satisfied
as in the case of a polygon of a thousand or a
hundred thousand sides. Such a polygon laid
upon a straight line touches it with one of its
sides, i. £., with one of its hundred thousand
parts; while the circle which is a polygon of an
infinite number of sides touches the same
straight line with one of its sides which is a
single point different from all its neighbors and
therefore separate and distinct in no less degree
than is one side of a polygon from the other
sides. And just as a polygon, when rolled along
a plane, marks out upon this plane, by the suc-
cessive contacts of its sides, a straight line equal
to its perimeter, so the circle rolled upon such
a plane also traces by its infinite succession of
contacts a straight line equal in length to its
own circumference. I am willing, Simplicio, at
the outset, to grant to the Peripatetics the truth
of their opinion that a continuous quantity is
divisible only into parts which are still further
divisible so that however far the division and
subdivision be continued no end will be reached ;
but I am not so certain that they will concede
to me that none of these divisions of theirs can
be a final one, as is surely the fact, because there
always remains "another"; the final and ulti-
mate division is rather one which resolves a
continuous quantity into an infinite number of
indivisible quantities, a result which I grant
can never be reached by successive division into
an ever-increasing number of parts. But if they
employ the method which I propose for sepa-
rating and resolving the whole 01 infinity, at a
single stroke (an artifice which surely ought not
to be denied me), I think that they would be
contented to admit that a continuous quantity
is built up out of absolutely indivisible atoms,
especially since this method, perhaps better
than any other, enables us to avoid many in-
tricate labyrinths, such as cohesion in solids, al-
ready mentioned, and the question of expansion
and contraction, without forcing upon us the
objectional admission of empty spaces which
carries with it the penetrability of bodies. Both
of these objections, it appears to me, are avoided
if we accept the above-mentioned view of indi-
visible constituents.
SIMP. I hardly know what the Peripatetics
would say since the views advanced by you
would strike them as mostly new, and as such
we must consider them. It is however, not un-
likely that they would find answers and solu-
tions for these problems which I, for want of
time and critical ability, am at present unable
to solve. Leaving this to one side for the mo-
ment, I should like to hear how the introduc-
tion of these indivisible quantities helps us to
understand contraction and expansion avoiding
at the same time the vacuum and the penetra-
bility of bodies.
SAGR. I also shall listen with keen interest to
this same matter which is far from clear in my
mind; provided I am allowed to hear what, a
moment ago, Simplicio suggested we omit,
namely, the reasons which Aristotle offers
against the existence of the vacuum and the ar-
guments which you must advance in rebuttal.
SALV. I will do both. And first, just as, for the
production of expansion, we employ the line de-
scribed by the small circle during one rotation
of the large one— a line greater than the circum-
ference of the small circle —so, in order to ex-
plain contraction, we point out that, during
each rotation of the smaller circle, the larger
one describes a straight line which is shorter
than its circumference.
For the better understanding of this we pro-
ceed to the consideration of what happens in
the case of polygons. Employing a figure simi-
lar to the earlier one, construct the two hexa-
gons, ABC and HIK, about the common centre
L, and let them roll along the parallel lines
HOM and ABc. Now holding the vertex I fixed,
allow the smaller polygon to rotate until the
side IK lies upon the parallel, during which mo-
tion the point K will describe the arc KM, and
152
GALILEO GALILEI
the side KI will coincide with 7M. Let us see
what, in the meantime, the side CB of the larger
polygon has been doing. Since the rotation is
about the point /, the terminal point B, of the
line IB, moving backwards, will describe the
arc Bb underneath the parallel cA so that when
the side KI coincides with the line MI, the side
BC will coincide with be, having advanced only
through the distance Be, but having retreated
through a portion of the line BA which subtends
the arc Bb. If we allow the rotation of the small-
er polygon to go on it will traverse and describe
along its parallel a line equal to its perimeter;
while the larger one will traverse and describe
a line less than its perimeter by as many times
the length bB as there are sides less one; this line
is approximately equal to that described by the
smaller polygon exceeding it only by the dis-
tance bB. Here now we see, without any diffi-
Fig.9
culty, why the larger polygon, when carried by
the smaller, does not measure off with its sides
a line longer than that traversed by the smaller
one; this is because a portion of each side is
superposed upon its immediately preceding
neighbour.
Let us next consider two circles, having a
common centre at A, and lying upon their re-
spective parallels, the smaller being tangent to
its parallel at the point B; the larger, at the point
C. Here when the small circle commences to
roll the point B does not remain at rest for a
while so as to allow BG to move backward and
carry with it the point C, as happened in the
case of the polygons, where the point / remained
fixed until the side KI coincided with MI and
the line IB carried the terminal point B back-
ward as far as b, so that the side BC fell upon
be, thus superposing upon the line BA, the por-
tion Bb, and advancing by an amount Be, equal
to Ml, that is, to one side of the smaller polygon.
On account of these superpositions, which are
the excesses of the sides of the larger over the
smaller polygon, each net advance is equal to
one side of the smaller polygon and, during
one complete rotation, these amount to a
straight line equal in length to the perimeter
of the smaller polygon.
But now reasoning in the same way concern-
ing the circles, we must observe that whereas
the number of sides in any polygon is comprised
within a certain limit, the number of sides in a
circle is infinite; the former are finite and divisi-
ble; the latter infinite and indivisible. In the
case of the polygon, the vertices remain at rest
during an interval of time which bears to the
period of one complete rotation the same ratio
which one side bears to the perimeter; likewise,
in the case of the circles, the delay of each of the
infinite number of vertices is merely instantane-
ous, because an instant is such a fraction of a fi-
nite interval as a point is of a line which con-
tains an infinite number of points. The retro-
gression of the sides of the larger polygon is not
equal to the length of one of its sides but merely
to the excess of such a side over one side of the
smaller polygon, the net advance being equal to
this smaller side; but in the circle, the point or
side C, during the instantaneous rest of B, re-
cedes by an amount equal to its excess over the
side B, making a net progress equal to B itself.
In short the infinite number of indivisible sides
of the greater circle with their infinite number
of indivisible retrogressions, made during the
infinite number of instantaneous delays of the
infinite number of vertices of the smaller circle,
together with the infinite number of progres-
sions, equal to the infinite number of sides in
the smaller circle — all these, I say, add up to a
line equal to that described by the smaller
circle, a line which contains an infinite num-
ber of infinitely small superpositions, thus
bringing about a thickening or contraction
without any overlapping or interpenetration
of finite parts. This result could not be obtained
in the case of a line divided into finite parts
THE TWO NEW SCIENCES
'53
such as is the perimeter of any polygon, which
when laid out in a straight line cannot be short-
ened except by the overlapping and interpen-
etration of its sides. This contraction of an
infinite number of infinitely small parts with-
out the interpenetration or overlapping of fi-
nite parts and the previously mentioned ex-
pansion of an infinite number of indivisible
parts by the interposition of indivisible vacua
is, in my opinion, the most that can be said con-
cerning the con traction and rarefaction of bodies,
unless we give up the impenetrability of matter
and introduce empty spaces of finite size. If
you find anything here that you consider worth
while, pray use it; if not regard it, together
with my remarks, as idle talk; but this remem-
ber, we are dealing with the infinite and the in-
divisible.
SAGR. I frankly confess that your idea is subtle
and that it impresses me as new and strange;
but whether, as a matter of fact, nature actually
behaves according to such a law I am unable to
determine; however, until I find a more satis-
factory explanation I shall hold fast to this one.
Perhaps Simplicio can tell us something which I
have not yet heard, namely, how to explain the
explanation which the philosophers have given
of this abstruse matter; for, indeed, all that I
have hitherto read concerning contraction is so
dense and that concerning expansion so thin that
my poor brain can neither penetrate the former
nor grasp the latter.
SIMP. I am all at sea and find difficulties in
following either path, especially this new one;
because according to this theory an ounce of
gold might be rarefied and expanded until its
size would exceed that of the earth, while the
earth, in turn, might be condensed and reduced
until it would become smaller than a walnut,
something which I do not believe; nor do I be-
lieve that you believe it. The arguments and
demonstrations which you have advanced are
mathematical, abstract, and far removed from
concrete matter; and I do not believe that when
applied to the physical and natural world these
laws will hold.
SALV. I am not able to render the invisible
visible, nor do I think that you will ask this.
But now that you mention gold, do not our
senses tell us that that metal can be immensely
expanded ? I do not know whether you have ob-
served the method employed by those who are
skilled in drawing gold wire, of which really
only the surface is gold, the inside material be-
ing silver. The way they draw it is as follows:
they take a cylinder or, if you please, a rod of
silver, about half a cubit long and three or four
times as wide as one's thumb; this rod they cover
with gold-leaf which is so thin that it almost
floats in air, putting on not more than eight
or ten thicknesses. Once gilded they begin to
pull it, with great force, through the holes of a
draw-plate; again and again it is made to pass
through smaller and smaller holes, until, after
very many passages, it is reduced to the fineness
of a lady's hair, or perhaps even finer; yet the
surface remains gilded. Imagine now how the
substance of this gold has been expanded and to
what fineness it has been reduced.
SIMP. I do not see that this process would pro-
duce, as a consequence, that marvellous thin-
ning of the substance of the gold which you sug-
gest: first, because the original gilding consist-
ing of ten layers of gold-leaf has a sensible thick-
ness; secondly, because in drawing out the silver
it grows in length but at the same time dimin-
ishes proportionally in thickness; and, since one
dimension thus compensates the other, the area
will not be so increased as to make it necessary
during the process of gilding to reduce the thin-
ness of the gold beyond that of the original leaves.
SALV. You are greatly mistaken, Simplicio,
because the surface increases directly as the
square root of the length, a fact which I can
demonstrate geometrically.
SAGR. Please give us the demonstration not
only for my own sake but also for Simplicio pro-
vided you think we can understand it.
SALV. I'll see if I can recall it on the spur of
the moment. At the outset, it is clear that the
original thick rod of silver and the wire drawn
out to an enormous length are two cylinders of
the same volume, since they are the same body
of silver. So that, if I determine the ratio be-
tween the surfaces of cylinders of the same
volume, the problem will be solved. I say then,
The areas of cylinders of equal volumes, neglect-
ing the bases, bear to each other a ratio which is
the square root of the ratio of their lengths.
Take two cylinders of equal volume having
the altitudes AB and CD, between which the
line £ is a mean proportional. Then I claim that,
omitting the bases of each cylinder, the surface
of the cylinder AB is to that of the cylinder CD
as the length AB is to the line E, that is, as the
square root of AB is to the square root of CD.
Now cut oil the cylinder AB at F so that the
altitude AFis equal to CD. Then since the bases
of cylinders of equal volume bear to one another
the inverse ratio of their heights, it follows that
the area of the circular base of the cylinder CD
will be to the area of the circular base of AB
'54
GALILEO GALILEI
B
I0
as the altitude BA is to DC: moreover, since
circles are to one another as the squares of
their diameters, the said squares will be to each
other as BA is to CD. But BA is to CD as
the square of BA is to the
square of E: and, therefore,
these foursquares will form
a proportion; and likewise
their sides; so the line AB
is to E as the diameter of
circle C is to the diameter
of the circle A. But the
diameters are proportion-
al to the circumferences
and the circumferences are
proportional to the areas of
cylinders of equal height;
hence the line AB is to E as
the surface of the cylinder
CD is to the surface of the cylinder AF. Now
since the height AF is \oAB as the surface of AF
is to the surface of AB] and since the height AB
is to the line Eas the surface CD is to AF, it fol-
lows, ex oequali in proportione perturbata1, that
the height AFis to £as the surface CD is to the
surface AB, and convertendo, the surface of the
cylinder AB is to the surface of the cylinder
CD as the line E is to AF, i. e., to CD, or as AB
is to E which is the square root of the ratio of
AB to CD. Q. E. D.
If now we apply these results to the case in
hand, and assume that the silver cylinder at the
time of gilding had a length of only half a cubit
and a thickness three or four times that of one's
thumb, we shall find that, when the wire has
been reduced to the fineness of a hair and has
been drawn out to a length of twenty thousand
cubits (and perhaps more), the area of its sur-
face will have been increased not less than two
hundred times. Consequently the ten leaves of
gold which were laid on have been extended
over a surface two hundred times greater, assur-
ing us that the thickness of the gold which now
covers the surface of so many cubits of wire can-
not be greater than one twentieth that of an or-
dinary leaf of beaten gold. Consider now what
degree of fineness it must have and whether one
could conceive it to happen in any other way
than by enormous expansion of parts; consider
also whether this experiment does not suggest
that physical bodies are composed of infinitely
small indivisible particles, a view which is sup-
ported by other more striking and conclusive
examples.
SAGR. This demonstration is so beautiful that,
1 See Euclid, v. 20.
even if it does not have the cogency originally
intended, — although tomy mind, it is very force-
ful—the short time devoted to it has neverthe-
less been most happily spent.
SALV. Since you are so fond of these geometri-
cal demonstrations, which carry with them dis-
tinct gain, I will give you a companion theorem
which answers an extremely interesting query.
We have seen above what relations hold between
equal cylinders of different height or length; let
us now see what holds when the cylinders are
equal in area but unequal in height, understand-
ing area to include the curved surface, but not
the upper and lower bases. The theorem is:
The volumes of right cylinders having equal
curved surf aces are inversely proportional to their
altitudes.
Let the surfaces of the two cylinders, AEznd
CF, be equal but let the height of the latter,
CD, be greater than that of the former, AB:
then I say that the volume of the cylinder AE is
to that of the cylinder CFas the height CD is to
AB. Now since the surface of CF is equal to the
surface of AE, it follows that the volume of CF
is less than that of AE', for, if they were equal,
the surface of CF would, by the preceding prop-
osition, exceed that oiAE, and the excess would
be so much the greater if the volume of the cyl-
inder CF were greater than that of AE. Let us
now take a cylinder ID having a volume equal
to that of AE-, then, according to the preceding
theorem, the surface of the cylinder ID is to the
surface of AEas the altitude /Fis to the mean
proportional between /Fand AB. But since one
THE TWO NEW SCIENCES
155
datum of the problem is that the surface of AE
is equal to that of CF, and since the surface ID
is to the surface CF as the altitude IF is to the
altitude CD, it follows that CD is a mean pro-
portional between IF and AE. Not only so, but
since the volume of the cylinder ID is equal to
that of AE, each will bear the same ratio to the
volume of the cylinder CF; but the volume ID
is to the volume CF as the altitude IF is to the
altitude CD; hence the volume of AEis to the
volume of CF as the length IF is to the length
CD, that is, as the length CD is to the length
AB. Q. E. D.
This explains a phenomenon upon which the
common people always look with wonder, name-
ly, if we have a piece of stuff which has one side
longer than the other, we can make from it a
cornsack, using the customary wooden base,
which will hold more when the short side of the
cloth is used for the height of the sack and the
long side is wrapped around the wooden base,
than with the alternative arrangement. So that,
for instance, from a piece of cloth which is six
cubits on one side and twelve on the other, a
sack can be made which will hold more when
the side of twelve cubits is wrapped around the
wooden base, leaving the sack six cubits high
than when the six cubit side is put around the
base making the sack twelve cubits high. From
what has been proven above we learn not only
the general fact that one sack holds more than
the other, but we also get specific and particular
information as to how much more, namely, just
in proportion as the altitude of the sack dimin-
ishes the contents increase and vice versa. Thus if
we use the figures given which make the cloth
twice as long as wide and if we use the long side
for the seam, the volume of the sack will be just
one-half as great as with the opposite arrange-
ment. Likewise if we have a piece of matting
which measures 7 x 25 cubits and make from it
a basket, the contents of the basket will, when
the seam is lengthwise, be seven as compared
with twenty-five when the seam runs endwise.
SAGR. It is with great pleasure that we con-
tinue thus to acquire new and useful informa-
tion. But as regards the subject just discussed, I
really believe that, among those who are not al-
ready familiar with geometry, you would scarce-
ly find four persons in a hundred who would not,
at first sight, make the mistake of believing that
bodies having equal surfaces would be equal in
other respects. Speaking of areas, the same error
is made when one attempts, as often happens, to
determine the sizes of various cities by measur-
ing their boundary lines, forgetting that the cir-
cuit of one may be equal to the circuit of an-
other while the area of the one is much greater
than that of the other. And this is true not only
in the case of irregular, but also of regular sur-
faces, where the polygon having the greater
number of sides always contains a larger area
than the one with the less number of sides, so
that finally the circle which is a polygon of an
infinite number of sides contains the largest area
of all polygons of equal perimeter. I remember
with particular pleasure having seen this dem-
onstration when I was studying the sphere of
Sacrobosco1 with the aid of a learned commen-
tary.
SALV. Very true! I too came across the same
passage which suggested to me a method of show-
ing how, by a single short demonstration, one
can prove that the circle has the largest content
of all regular isoperimetric figures; and that, of
other figures, the one which has the larger num-
ber of sides contains a greater area than that
which has the smaller number.
SAGR. Being exceedingly fond of choice and
uncommon propositions, I beseech you to let us
have your demonstration.
SALV. I can do this in a few words by proving
the following theorem:
The area of a circle is a mean proportional be-
tween any two regular and similar polygons of
which one circumscribes it and the other is iso-
perimetric with it. In addition, the area of the
circle is less than that of any circumscribed poly-
gon and greater than that of any isoperimetric
polygon. And further, of these circumscribed
polygons, the one which has the greater number
of sides is smaller than the one which has a less
number; but, on the other hand, that isoperi-
metric polygon which has the greater number of
sides is the larger.
Let A and B be two similar polygons of which
A circumscribes the given circle and B is iso-
perimetric with it. The area of the circle will
then be a mean proportional between the areas
of the polygons. For if we indicate the radius of
the circle by AC and if we remember that the
area of the circle is equal to that of a right-
angled triangle in which one of the sides about
the right angle is equal to the radius, AC, and
the other to the circumference; and if likewise
we remember that the area of the polygon A is
equal to the area of a right-angled triangle one
of whose sides about the right angle has the same
length as ^Cand the other is equal to the per-
imeter of the polygon itself; it is then manifest
1 John of Holywood, English mathematician, was
known as Johannes de Sacro Bosco. — ED.
i56
GALILEO GALILEI
Fig. 12
that the circumscribed polygon bears to the cir-
cle the same ratio which its perimeter bears to
the circumference of the circle, or to the peri-
meter of the polygon B which is, by hypothesis,
equal to the circumference of the circle. But
since the polygons A and B are similar their
areas are to each other as the squares of their
perimeters; hence the area of the circle A is a
mean proportional between the areas of the
two polygons A and B. And since the area of
the polygon A is greater than that of the circle
A, it is clear that the area of the circle A is
greater than that of the isoperimetric polygon
By and is therefore the greatest of all regular
polygons having the same perimeter as the
circle.
We now demonstrate the remaining portion
of the theorem, which is to prove that, in the
case of polygons circumscribing a given circle,
the one having the smaller number of sides has
a larger area than one having a greater number
of sides; but that on the other hand, in the case
of isoperimetric polygons, the one having the
more sides has a larger area than the one with
less sides. To the circle which has 0 for centre
and OA for radius draw the tangent AD; and
on this tangent lay off, say, AD which shall
represent one-half of the side of a circumscribed
pentagon and A C which shall represent one-half
of the side of a heptagon; draw the straight
lines OGC and OFD\ then with 0 as a centre
and OC as radius draw the arc ECL Now since
the triangle DOC is greater than the sector EOC
and since the sector COI is greater than the
triangle CO A, it follows that the triangle DOC
bears to the triangle CO A a greater ratio than
the sector EOC bears to the sector CO/, that is,
than the sector FOG bears to the sector GOA.
Hence, componcndo et permutando> the triangle
DOA bears to the sector FOA a greater ratio
than that which the triangle COA bears to the
sector GO A, and also 10 such triangles DOA
bear to 10 such sectors FOA a greater ratio than
14 such triangles COA bear to 14 such sectors
j that is to say, the circumscribed penta-
gon bears to the circle a greater ratio than does
the heptagon. Hence the pentagon exceeds the
heptagon in area.
But now let us assume that both the hepta-
gon and the pentagon have the same perimeter
as that of a given circle. Then I say the hepta-
gon will contain a larger area than the penta-
gon. For since the area of the circle is a mean
proportional between areas of the circumscribed
and of the isoperimetric pentagons, and since
likewise it is a mean proportional between the
circumscribed and isoperimetric heptagons,
and since also we have proved that the circum-
scribed pentagon is larger than the circum-
scribed heptagon, it follows that this circum-
scribed pentagon bears to the circle a larger
ratio than does the heptagon, that is, the circle
will bear to its isoperimetric pentagon a greater
ratio than to its isoperimetric heptagon. Hence
the pentagon is smaller than its isoperimetric
heptagon. Q. E. D.
SACK. A very clever and elegant demonstra-
tion! But how did we come to plunge into ge-
ometry while discussing the objections urged
by Simplicio, objections of great moment, es-
pecially that one referring to density which
strikes me as particularly difficult?
SALV. If contraction and expansion consist in
contrary motions, one ought to find for each
great expansion a correspondingly large con-
traction. But our surprise is increased when,
every day, we see enormous expansions taking
place almost instantaneously. Think what a tre-
mendous expansion occurs when a small quan-
tity of gun-powder flares up into a vast volume
of fire! Think too of the almost limitless expan-
sion of the light which it produces! Imagine the
contraction which would take place if this fire
and this light were to reunite, which, indeed,
is not impossible since only a little while ago
they were located together in this small space.
You will find, upon observation, a thousand
such expansions for they are more obvious than
contractions since dense matter is more palpa-
ble and accessible to our senses. We can take
THE TWO NEW SCIENCES
'57
wood and see it go up in fire and light, but we
do not see them recombine to form wood; we
see fruits and flowers and a thousand other solid
bodies dissolve largely into odours, but we do
not observe these fragrant atoms coming to-
gether to form fragrant solids. But where the
senses fail us reason must step in; for it will
enable us to understand the motion involved
in the condensation of extremely rarefied and
tenuous substances just as clearly as that in-
volved in the expansion and dissolution of so-
lids. Moreover we are trying to find out how
it is possible to produce expansion and con-
traction in bodies which are capable of such
changes without introducing vacua and with-
out giving up the impenetrability of matter;
but this does not exclude the possibility of
there being materials which possess no such
properties and do not, therefore, carry with
them consequences which you call inconve-
nient and impossible. And finally, Simplicio,
I have, for the sake of you philosophers, taken
pains to find an explanation of how expan-
sion and contraction can take place without
our admitting the penetrability of matter and
introducing vacua, properties which you deny
and dislike; if you were to admit them, I should
not oppose you so vigorously. Now either ad-
mit these difficulties or accept my views or sug-
gest something better.
SAGR, I quite agree with the peripatetic phi-
losophers in denying the penetrability of mat-
ter. As to the vacua I should like to hear a
thorough discussion of Aristotle's demonstra-
tion in which he opposes them, and what you,
Sal via ti, have to say in reply. I beg of you,
Simplicio, that you give us the precise proof
of the Philosopher and that you, Salviati, give
us the reply.
SIMP. So far as I remember, Aristotle inveighs
against the ancient view that a vacuum is a
necessary prerequisite for motion and that the
latter could not occur without the former. In
opposition to this view Aristotle shows that it
is precisely the phenomenon of motion, as we
shall see, which renders untenable the idea of a
vacuum. His method is to divide the argument
into two parts. He first supposes bodies of dif-
ferent weights to move in the same medium;
then supposes, one and the same body to move
in different media. In the first case, he supposes
bodies of different weight to move in one and
the same medium with different speeds which
stand to one another in the same ratio as the
weights; so that, for example, a body which is
ten times as heavy as another will move ten
times as rapidly as the other. In the second case,
he assumes that the speeds of one and the same
body moving in different media are in inverse
ratio to the densities of these media; thus, for
instance, if the density of water were ten times
that of air, the speed in air would be ten times
greater than in water. From this second suppo-
sition, he shows that, since the tenuity of a
vacuum differs infinitely from that of any me-
dium filled with matter however rare, any body
which moves in a plenum through a certain
space in a certain time ought to move through
a vacuum instantaneously; but instantaneous
motion is an impossibility; it is therefore im-
possible that a vacuum should be produced by
motion.
SALV. The argument is, as you see, ad homi-
nem, that is, it is directed against those who
thought the vacuum a prerequisite for motion.
Now, if I admit the argument to be conclusive
and concede also that motion cannot take place
in a vacuum, the assumption of a vacuum con-
sidered absolutely and not with reference to
motion, is not thereby invalidated. But to tell
you what the ancients might possibly have re-
plied and in order to better understand just
how conclusive Aristotle 's demonstration is, we
may, in my opinion, deny both of his assump-
tions. And as to the first, I greatly doubt that
Aristotle ever tested by experiment whether it
be true that two stones, one weighing ten times
as much as the other, if allowed to fall, at the
same instant, from a height of, say, 100 cubits,
would so differ in speed that when the heavier
had reached the ground, the other would not
have fallen more than 10 cubits.
SIMP. His language would seem to indicate
that he had tried the experiment, because he
says: We see the heavier', now the word see shows
that he had made the experiment.
SAGR. But I, Simplicio, who had made the
test can assure you that a cannon ball weighing
one or two hundred pounds, or even more, will
not reach the ground by as much as a span
ahead of a musket ball weighing only half a
pound, provided both are dropped from a
height of 200 cubits.
SALV. But, even without further experiment,
it is possible to prove clearly, by means of a
short and conclusive argument, that a heavier
body does not move more rapidly than a lighter
one provided both bodies are of the same mate-
rial and in short such as those mentioned by
Aristotle. But tell me, Simplicio, whether you
admit that each falling body acquires a definite
speed fixed by nature, a velocity which cannot
158
GALILEO GALILEI
be increased or diminished except by the use of
force or resistance.
SiMP.There can be no doubt but that one and
the same body moving in a single medium has
a fixed velocity which is determined by nature
and which cannot be increased except by the
addition of momentum or diminished except by
some resistance which retards it.
SALV. If then we take two bodies whose natu-
ral speeds are different, it is clear that on unit-
ing the two, the more rapid one will be partly
retarded by the slower, and the slower will be
somewhat hastened by the swifter. Do you not
agree with me in this opinion ?
SIMP. You are unquestionably right.
SALV. But if this is true, and if a large stone
moves with a speed of, say, eight while a smaller
moves with a speed of four, then when they arc
united, the system will move with a speed less
than eight; but the two stones when tied to-
gether make a stone larger than that which be-
fore moved with a speed of eight. Hence the
heavier body moves with less speed than the
lighter; an effect which is contrary to your sup-
position. Thus you see how, from your assump-
tion that the heavier body moves more rapidly
than the lighter one, I infer that the heavier
body moves more slowly.
SIMP. I am all at sea because it appears to me
that the smaller stone when added to the larger
increases its weight and by adding weight I do
not see how it can fail to increase its speed or,
at least, not to diminish it.
SALV. Here again you are in error, Simplicio,
because it is not true that the smaller stone adds
weight to the larger.
SIMP. This is, indeed, quite beyond my com-
prehension.
SALV. It will not be beyond you when I have
once shown you the mistake under which you
are labouring. Note that it is necessary to dis-
tinguish between heavy bodies in motion and
the same bodies at rest. A large stone placed in
a balance not only acquires additional weight
by having another stone placed upon it, but
even by the addition of a handful of hemp its
weight is augmented six to ten ounces according
to the quantity of hemp. But if you tie the
hemp to the stone and allow them to fall freely
from some height, do you believe that the hemp
will press down upon the stone and thus accel-
erate its motion or do you think the motion
will be retarded by a partial upward pressure?
One always feels the pressure upon his shoul-
ders when he prevents the motion of a load
resting upon him; but if one descends just as
rapidly as the load would fall how can it grav-
itate or press upon him? Do you not see that
this would be the same as trying to strike a man
with a lance when he is running away from you
with a speed which is equal to, or even greater,
than that with which you are following him?
You must therefore conclude that, during free
and natural fall, the small stone does not press
upon the larger and consequently does not in-
crease its weight as it does when at rest.
SIMP. But what if we should place the larger
stone upon the smaller ?
SALV. Its weight would be increased if the
larger stone moved more rapidly; but we have
already concluded that when the small stone
moves more slowly it retards to some extent the
speed of the larger, so that the combination of
the two, which is a heavier body than the larger
of the two stones, would move less rapidly, a
conclusion which is contrary to your hypothe-
sis. We infer therefore that large and small bod-
ies move with the same speed provided they
are of the same specific gravity.
SIMP. Your discussion is really admirable;
yet I do not find it easy to believe that a bird-
shot falls as swiftly as a cannon ball.
SALV. Why not say a grain of sand as rapidly
as a grindstone ? But, Simplicio, I trust you will
not follow the example of many others who di-
vert the discussion from its main intent and
fasten upon some statement of mine which lacks
a hairVbreadth of the truth and, under this
hair, hide the fault of another which is as big as
a ship's cable. Aristotle says that "an iron ball
of one hundred pounds falling from a height of
one hundred cubits reaches the ground before
a one-pound ball has fallen a single cubit." I say
that they arrive at the same time. You find, on
making the experiment, that the larger out-
strips the smaller by two finger-breadths, that
is, when the larger has reached the ground, the
other is short of it by two finger- breadths; now
you would not hide behind these two fingers the
ninety-nine cubits of Aristotle, nor would you
mention my small error and at the same time
pass over in silence his very large one. Aristotle
declares that bodies of different weights, in the
same medium, travel (in so far as their motion
depends upon gravity) with speeds which are
proportional to their weights; this he illustrates
by use of bodies in which it is possible to per-
ceive the pure and unadulterated effect of gravi-
ty, eliminating other considerations, for ex-
ample, figure as being of small importance, in-
fluences which are greatly dependent upon the
medium which modifies the single effect of
THE TWO NEW SCIENCES
159
gravity alone. Thus we observe that gold, the
densest of all substances, when beaten out into
a very thin leaf, goes floating through the air;
the same thing happens with stone when ground
into a very fine powder. But if you wish to
maintain the general proposition you will have
to show that the same ratio of speeds is pre-
served in the case of all heavy bodies, and that a
stone of twenty pounds moves ten times as
rapidly as one of two; but I claim that this is
false and that, if they fall from a height of fifty
or a hundred cubits, they will reach the earth
at the same moment.
SIMP. Perhaps the result would be different
if the fall took place not from a few cubits but
from some thousands of cubits.
SALV. If this were what Aristotle meant you
would burden him with another error which
would amount to a falsehood; because, since
there is no such sheer height available on earth,
it is clear that Aristotle could not have made
the experiment; yet he wishes to give us the
impression of his having performed it when
he speaks of such an effect as one which we
see.
SIMP. In fact, Aristotle does not employ this
principle, but uses the other one which is not,
I believe, subject to these same difficulties.
SALV. But the one is as false as the other; and
I am surprised that you yourself do not see the
fallacy and that you do not perceive that if it
were true that, in media of different densities
and different resistances, such as water and air,
one and the same body moved in air more rap-
idly than in water, in proportion as the density
of water is greater than that of air, then it
would follow that any body which falls through
air ought also to fall through water. But this
conclusion is false inasmuch as many bodies
which descend in air not only do not descend in
water, but actually rise.
SIMP. I do not understand the necessity of
your inference; and in addition I will say that
Aristotle discusses only those bodies which fall
in both media, not those which fall in air but
rise in water.
SALV. The arguments which you advance for
the Philosopher are such as he himself would
have certainly avoided so as not to aggravate
his first mistake. But tell me now whether the
density of the water, or whatever it may be that
retards the motion, bears a definite ratio to the
density of air which is less retardative; and if
so fix a value for it at your pleasure.
SIMP. Such a ratio does exist; let us assume it
to be ten; then, for a body which falls in both
these media, the speed in water will be ten times
slower than in air.
SALV. I shall now take one of those bodies
which fall in air but not in water, say a wooden
ball, and I shall ask you to assign to it any speed
you please for its descent through air.
SIMP. Let us suppose it moves with a speed of
twenty.
SALV. Very well. Then it is clear that this
speed bears to some smaller speed the same ratio
as the density of water bears to that of air; and
the value of this smaller speed is two. So that
really if we follow exactly the assumption of
Aristotle we ought to infer that the wooden
ball which falls in air, a substance ten times less-
resisting than water, with a speed of twenty
would fall in water with a speed of two, instead
of coming to the surface from the bottom as it
does; unless perhaps you wish to reply, which
I do not believe you will, that the rising of the
wood through the water is the same as its falling
with a speed of two. But since the wooden ball
does not go to the bottom, I think you will
agree with me that we can find a ball of another
material, not wood, which does fall in water
with a speed of two.
SIMP. Undoubtedly we can; but it must be of
a substance considerably heavier than wood.
SALV. That is it exactly. But if this second
ball falls in water with a speed of two, what will
be its speed of descent in air? If you hold to the
rule of Aristotle you must reply that it will
move at the rate of twenty; but twenty is the
speed which you yourself have already assigned
to the wooden ball; hence this and the other
heavier ball will each move through air with
the same speed. But now how does the Philoso-
pher harmonize this result with his other, name-
ly, that bodies of different weight move through
the same medium with different speeds — speeds
which are proportional to their weights? But
without going into the matter more deeply, how
have these common and obvious properties es-
caped your notice ? Have you not observed that
two bodies which fall in water, one with a speed
a hundred times as great as that of the other,
will fall in air with speeds so nearly equal that
one will not surpass the other by as much as one
hundredth part? Thus, for example, an egg
made of marble will descend in water one hun-
dred times more rapidly than a hen's egg, while
in air falling from a height of twenty cubits the
one will fall short of the other by less than four
finger-breadths. In short, a heavy body which
sinks through ten cubits of water in three hours
will traverse ten cubits of air in one or two
i6o
GALILEO GALILEI
pulse-beats; and if the heavy body be a ball of
lead it will easily traverse the ten cubits of wa-
ter in less than double the time required for ten
cubits of air. And here, I am sure, Simplicio, you
find no ground for difference or objection. We
conclude, therefore, that the argument does
not bear against the existence of a vacuum; but
if it did, it would only do away with vacua of
considerable size which neither I nor, in my
opinion, the ancients ever believed to exist in
nature, although they might possibly be pro-
duced by force as may be gathered from various
experiments whose description would here oc-
cupy too much time.
SAGR. Seeing that Simplicio is silent, I will
take the opportunity of saying something.
Since you have clearly demonstrated that bod-
ies of different weights do not move in one and
the same medium with velocities proportional
to their weights, but that they all move with
the same speed, understanding of course that
they are of the same substance or at least of the
same specific gravity; certainly not of different
specific gravities, for I hardly think you would
have us believe a ball of cork moves with the
same speed as one of lead ; and again since you
have clearly demonstrated that one and the
same body moving through differently resisting
media does not acquire speeds which are in-
versely proportional to the resistances, I am
curious to learn what are the ratios actually
observed in these cases.
SALV. These are interesting questions and I
have thought much concerning them. I will
give you the method of approach and the result
which I finally reached. Having once estab-
lished the falsity of the proposition that one
and the same body moving through differently
resisting media acquires speeds which are in-
versely proportional to the resistances of these
media, and having also disproved the statement
that in the same medium bodies of different
weight acquire velocities proportional to their
weights (understanding that this applies also to
bodies which differ merely in specific gravity),
I then began to combine these two facts and to
consider what would happen if bodies of differ-
ent weight were placed in media of different
resistances; and I found that the differences in
speed were greater in those media which were
more resistant, that is, less yielding. This differ-
ence was such that two bodies which differed
scarcely at all in their speed through air would,
in water, fall the one with a speed ten times as
great as that of the other. Further, there are
bodies which will fall rapidly in air, whereas if
placed in water not only will not sink but will
remain at rest or will even rise to the top: for it
is possible to find some kinds of wood, such as
knots and roots, which remain at rest in water
but fall rapidly in air.
SAGR. I have often tried with the utmost
patience to add grains of sand to a ball of wax
until it should acquire the same specific gravity
as water and would therefore remain at rest in
this medium. But with all my care I was never
able to accomplish this. Indeed, I do not know
whether there is any solid substance whose
specific gravity is, by nature, so nearly equal to
that of water that if placed anywhere in water
it will remain at rest.
SALV. In this, as in a thousand other opera-
tions, men are surpassed by animals. In this
problem of yours one may learn much from the
fish which are very skillful in maintaining their
equilibrium not only in one kind of water, but
also in waters which are notably different erther
by their own nature or by some accidental
muddiness or through salinity, each of which
produces a marked change. So perfectly indeed
can fish keep their equilibrium that they are
able to remain motionless in any position. This
they accomplish, I believe, by means of an ap-
paratus especially provided by nature, namely,
a bladder located in the body and communicat-
ing with the mouth by means of a narrow tube
through which they are able, at will, to expel
a portion of the air contained in the bladder: by
rising to the surface they can take in more air;
thus they make themselves heavier or lighter
than water at will and maintain equilibrium.
SAGR. By means of another device I was able
to deceive some friends to whom I had boasted
that I could make up a ball of wax that would
be in equilibrium in water. In the bottom of a
vessel I placed some salt water and upon this
some fresh water; then I showed them that the
ball stopped in the middle of the water, and
that, when pushed to the bottom or lifted to
the top, would not remain in either of these
places but would return to the middle.
SALV. This experiment is not without useful-
ness. For when physicians are testing the vari-
ous qualities of waters, especially their specific
gravities, they employ a ball of this kind so ad-
justed that, in certain water, it will neither rise
nor fall. Then in testing another water, differ-
ing ever so slightly in specific gravity, the ball
will sink if this water be lighter and rise if it be
heavier. And so exact is this experiment that
the addition of two grains of salt to six pounds
of water is sufficient to make the ball rise to the
THE TWO NEW SCIENCES
161
surface from the bottom to which it had fallen.
To illustrate the precision of this experiment
and also to clearly demonstrate the non-resist-
ance of water to division, I wish to add that
this notable difference in specific gravity can
be produced not only by solution of some
heavier substance, but also by merely heating
or cooling; and so sensitive is water to this proc-
ess that by simply adding four drops of another
water which is slightly warmer or cooler than
the six pounds one can cause the ball to sink or
rise; it will sink when the warm water is poured
in and will rise upon the addition of cold water.
Now you can see how mistaken are those phil-
osophers who ascribe to water viscosity or some
other coherence of parts which offers resistance
to separation of parts and to penetration.
SAGR. With regard to this question I have
found many convincing arguments in a treatise
by our Academician; but there is one great dif-
ficulty of which I have not been able to rid my-
self, namely, if there be no tenacity or coher-
ence between the particles of water how is it
possible for those large drops of water to stand
out in relief upon cabbage leaves without scat-
tering or spreading out ?
SALV. Although those who are in possession of
the truth are able to solve all objections raised,
I would not arrogate to myself such power; nev-
ertheless my inability should not be allowed to
becloud the truth. To begin with let me confess
that I do not understand how these large glob-
ules of water stand out and hold themselves up,
although I know for a certainty, that it is not
owing to any internal tenacity acting between
the particles of water; whence it must follow
that the cause of this effect is external. Beside
the experiments already shown to prove that
the cause is not internal, I can offer another
which is very convincing. If the particles of wa-
ter which sustain themselves in a heap, while
surrounded by air, did so in virtue of an internal
cause then they would sustain themselves much
more easily when surrounded by a medium in
which they exhibit less tendency to fall than
they do in air; such a medium would be any
fluid heavier than air, as, for instance, wine: and
therefore if some wine be poured about such a
drop of water, the wine might rise until the drop
was entirely covered, without the particles of
water, held together by this internal coherence,
ever parting company. But this is not the fact;
for as soon as the wine touches the water, the
latter without waiting to be covered scatters
and spreads out underneath the wine if it be
red. The cause of this effect is therefore external
and is possibly to be found in the surrounding
air. Indeed there appears to be a considerable
antagonism between air and water as I have ob-
served in the following experiment. Having tak-
en a glass globe which had a mouth of about the
same diameter as a straw, I filled it with water
and turned it mouth downwards; nevertheless,
the water, although quite heavy and prone to
descend, and the air, which is very light and
disposed to rise through the water, refused, the
one to descend and the other to ascend through
the opening, but both remained stubborn and
defiant. On the other hand, as soon as I apply to
this opening a glass of red wine, which is almost
inappreciably lighter than water, red streaks are
immediately observed to ascend slowly through
the water while the water with equal slowness
descends through the wine without mixing, un-
til finally the globe is completely filled with
wine and the water has all gone down into the
vessel below. What then can we say except that
there exists, between water and air, a certain in-
compatibility which I do not understand, but
perhaps. . . .
SIMP. I feel almost like laughing at the great
antipathy which Salviati exhibits against the use
of the word antipathy; and yet it is excellently
adapted to explain the difficulty.
SALV. Alright, if it please Simplicio, let this
word antipathy be the solution of our difficulty.
Returning from this digression, let us again take
up our problem. We have already seen that the
difference of speed between bodies of different
specific gravities is most marked in those media
which are the most resistant : thus, in a medium
of quicksilver, gold not merely sinks to the bot-
tom more rapidly than lead but it is the only
substance that will descend at all; all other met-
als and stones rise to the surface and float. On
the other hand, the variation of speed in air be-
tween balls of gold, lead, copper, porphyry, and
other heavy materials is so slight that in a fall of
100 cubits a ball of gold would surely not out-
strip one of copper by as much as four fingers.
Having observed this I came to the conclusion
that in a medium totally devoid of resistance all
bodies would fall with the same speed.
SIMP. This is a remarkable statement, Salvi-
ati. But I shall never believe that even in a vacu-
um, if motion in such a place were possible, a
lock of wool and a bit of lead can fall with the
same velocity.
SALV. A little more slowly, Simplicio. Your
difficulty is not so recondite nor am I so impru-
dent as to warrant you in believing that I have
not already considered this matter and found
162
GALILEO GALILEI
the proper solution. Hence for my justification
and for your enlightenment hear what I have to
say. Our problem is to find out what happens to
bodies of different weight moving in a medium
devoid of resistance, so that the only difference
in speed is that which arises from inequality of
weight. Since no medium except one entirely
free from air and other bodies, be it ever so ten-
uous and yielding, can furnish our senses with
the evidence we are looking for, and since such
a medium is not available, we shall observe what
happens in the rarest and least resistant media
as compared with what happens in denser and
more resistant media. Because if we find as a
fact that the variation of speed among bodies
of different specific gravities is less and less ac-
cording as the medium becomes more and
more yielding, and if finally in a medium of ex-
treme tenuity, though not a perfect vacuum,
we find that, in spite of great diversity of
specific gravity, the difference in speed is very
small and almost inappreciable, then we are
justified in believing it highly probable that
in a vacuum all bodies would fall with the same
speed. Let us, in view of this, consider what
takes place in air, where for the sake of a def-
inite figure and light material imagine an in-
flated bladder. The air in this bladder when sur-
rounded by air will weigh little or nothing, since
it can be only slightly compressed; its weight
then is small being merely that of the skin which
does not amount to the thousandth part of a
mass of lead having the same size as the inflated
bladder. Now, Simplicio, if we allow these two
bodies to fall from a height of four or six cubits,
by what distance do you imagine the lead will
anticipate the bladder? You may be sure that
the lead will not travel three times, or even
twice, as swiftly as the bladder, although you
would have made it move a thousand times as
rapidly.
SIMP. It may be as you say during the first
four or six cubits of the fall; but after the mo-
tion has continued a long while, I believe that
the lead will have left the bladder behind not
only six out of twelve parts of the distance but
even eight or ten.
SALV. I quite agree with you and doubt not
that, in very long distances, the lead might cover
one hundred miles while the bladder was trav-
ersing one; but, my dear Simplicio, this phe-
nomenon which you adduce against my propo-
sition is precisely the one which confirms it. Let
me once more explain that the variation of speed
observed in bodies of different specific gravities
is not caused by the difference of specific gravity
but depends upon external circumstances and,
in particular, upon the resistance of the medi-
um, so that if this is removed all bodies would
fall with the same velocity; and this result I de-
duce mainly from the fact which you have just
admitted and which is very true, namely, that,
in the case of bodies which differ widely in weight,
their velocities differ more and more as the spaces
traversed increase, something which would not
occur if the effect depended upon differences of
specific gravity. For since these specific gravities
remain constant, the ratio between the distances
traversed ought to remain constant whereas the
fact is that this ratio keeps on increasing as the
motion continues. Thus a very heavy body in
a fall of one cubit will not anticipate a very
light one by so much as the tenth part of this
space; but in a fall of twelve cubits the heavy
body would outstrip the other by one-third,
and in a fall of one hundred cubits by 90/100,
etc.
SIMP. Very well: but, following your own line
of argument, if differences of weight in bodies of
different specific gravities cannot produce a
change in the ratio of their speeds, on the ground
that their specific gravities do not change, how
is it possible for the medium, which also we sup-
pose to remain constant, to bring about any
change in the ratio of these velocities ?
SALV. This objection with which you oppose
my statement is clever; and I must meet it. I
begin by saying that a heavy body has an in-
herent tendency to move with a constantly and
uniformly accelerated motion toward the com-
mon center of gravity, that is, toward the center
of our earth, so that during equal intervals of
time it receives equal increments of momentum
and velocity. This, you must understand, holds
whenever all external and accidental hindrances
have been removed; but of these there is one
which we can never remove, namely, the medi-
um which must be penetrated and thrust aside by
the falling body. This quiet, yielding, fluid me-
dium opposes motion through it with a resist-
ance which is proportional to the rapidity with
which the medium must give way to the passage
of the body; which body, as I have said, is by
nature continuously accelerated so that it meets
with more and more resistance in the medium
and hence a diminution in its rate of gain of
speed until finally the speed reaches such a point
and the resistance of the medium becomes so
great that, balancing each other, they prevent
any further acceleration and reduce the motion
of the body to one which is uniform and which
will thereafter maintain a constant value. There
THE TWO NEW SCIENCES
163
is, therefore, an increase in the resistance of the
medium, not on account of any change in its
essential properties, buton account of the change
in rapidity with which it must yield and give
way laterally to the passage of the falling body
which is being constantly accelerated.
Now seeing how great is the resistance which
the air offers to the slight momentum of the
bladder and how small that which it offers to
the large weight of the lead, I am convinced
that, if the medium were entirely removed, the
advantage received by the bladder would be so
great and that coming to the lead so small that
their speeds would be equalized. Assuming this
principle, that all falling bodies acquire equal
speeds in a medium which, on account of a vac-
uum or something else, offers no resistance to
the speed of the motion, we shall be able ac-
cordingly to determine the ratios of the speeds
of both similar and dissimilar bodies moving
either through one and the same medium or
through different space-filling, and therefore re-
sistant, media. This result we may obtain by
observing how much the weight of the medium
detracts from the weight of the moving body,
which weight is the means employed by the fall-
ing body to open a path for itself and to push
aside the parts of the medium, something which
does not happen in a vacuum where, therefore,
no difference is to be expected from a difference
of specific gravity. And since it is known that
theeffectof the medium is todiminish the weight
of the body by the weight of the medium dis-
placed, we may accomplish our purpose by di-
minishing in just this proportion the speeds of
the falling bodies, which in a non-resisting me-
dium we have assumed to be equal.
Thus, for example, imagine lead to be ten
thousand times as heavy as air while ebony is
only one thousand times as heavy. Here we have
two substances whose speeds of fall in a medium
devoid of resistance are equal: but, when air is
the medium, it will subtract from the speed of
the lead one part in ten thousand, and from the
Speed of the ebony one part in one thousand,
;'. e. ten parts in ten thousand. While therefore,
lead and ebony would fall from any given height
in the same interval of time, provided the re-
tarding effect of the air were removed, the lead
will, in air, lose in speed one part in ten thou-
sand; and the ebony, ten parts in ten thousand.
In other words, if the elevation from which the
bodies start be divided into ten thousand parts,
the lead will reach the ground leaving the ebony
behind by as much as ten, or at least nine, of
these parts. Is it not clear then that a leaded ball
allowed to fall from a tower two hundred cubits
high will outstrip an ebony ball by less than
four inches ? Now ebony weighs a thousand times
as much as air but this inflated bladder only four
times as much; therefore air diminishes the in-
herent and natural speed of ebony by one part
in a thousand; while that of the bladder which,
if free from hindrance, would be the same, ex-
periences a diminution in air amounting to one
part in four. So that when the ebony ball, fall-
ing from the tower, has reached the earth, the
bladder will have traversed only three-quarters
of this distance. Lead is twelve times as heavy
as water; but ivory is only twice as heavy. The
speeds of these two substances which, when en-
tirely unhindered, are equal will be diminished
in water, that of lead by one part in twelve,
that of ivory by half. Accordingly, when the
lead has fallen through eleven cubits of water
the ivory will have fallen through only six. Em-
ploying this principle we shall, I believe, find a
much closer agreement of experiment with our
computation than with that of Aristotle.
In a similar manner we may find the ratio of
the speeds of one and the same body in different
fluid media, not by comparing the different re-
sistances of the media, but by considering the
excess of the specific gravity of the body above
those of the media. Thus, for example, tin is one
thousand times heavier than air and ten times
heavier than water; hence, if we divide its un-
hindered speed into 1000 parts, air will rob it of
one of these parts so that it will fall with a speed
of 999, while in water its speed will be 900, see-
ing that water diminishes its weight by one part
in ten while air by only one part in a thousand.
Again take a solid a little heavier than water,
such as oak, a ball of which will weigh let us say
1000 drachms; suppose an equal volume of wa-
ter to weigh 950, and an equal volume of air, 2;
then it is clear that if the unhindered speed of
the ball is 1000, its speed in air will be 998, but
in water only 50, seeing that the water removes
950 of the rooo parts which the body weighs,
leaving only 50.
Such a solid would therefore move almost
twenty times as fast in air as in water, since its
specific gravity exceeds that of water by one
part in twenty. And here we must consider the
fact that only those substances which have a
specific gravity greater than water can fall
through it— substances which must, therefore,
be hundreds of times heavier than air; hence
when we try to obtain the ratio of the speed in
air to that in water, we may, without appreci-
able error, assume that air does not, to any con-
i64
GALILEO GALILEI
siderable extent, diminish the free weight, and
consequently the unhindered speed of such sub-
stances. Having thus easily found the excess of
the weight of these substances over that of wa-
ter, we can say that their speed in air is to their
speed in water as their free weight is to the ex-
cess of this weight over that of water. For ex-
ample, a ball of ivory weighs 20 ounces; an equal
volume of water weighs 17 ounces; hence the
speed of ivory in air bears to its speed in water
the approximate ratio of 20:3.
SAGR. I have made a great step forward in this
truly interesting subject upon which I have long
laboured in vain. In order to put these theories
into practice we need only discover a method of
determining the specific gravity of air with ref-
erence to water and hence with reference to
other heavy substances.
SIMP. But if we find that air has levity instead
of gravity what then shall we say of the forego-
ing discussion which, in other respects, is very
clever?
SALV. I should say that it was empty, vain, and
trifling. But can you doubt that air has weight
when you have the clear testimony of Aristotle
affirming that all the elements have weight in-
cluding air, and excepting only fire ? As evidence
of this he cites the fact that a leather bottle
weighs more when inflated than when collapsed.
SIMP. I am inclined to believe that the in-
crease of weight observed in the inflated leather
bottle or bladder arises, not from the gravity of
the air, but from the many thick vapours mingled
with it in these lower regions. To this I would
attribute the increase of weight in the leather
bottle.
SALV. I would not have you say this, and much
less attribute it to Aristotle; because, if speak-
ing of the elements, he wished to persuade me
by experiment that air has weight and were to
say to me: "Take a leather bottle, fill it with
heavy vapours and observe how its weight in-
creases," I would reply that the bottle would
weigh still more if filled with bran; and would
then add that this merely proves that bran and
thick vapours are heavy, but in regard to air I
should still remain in the same doubt as before.
However, the experiment of Aristotle is good
and the proposition is true. But I cannot say as
much of a certain other consideration, taken at
face value; this consideration was offered by a
philosopher whose name slips me; but I know I
have read his argument which is that air exhib-
its greater gravity than levity, because it car-
ries heavy bodies downward more easily than it
does light ones upward.
SAGR. Fine indeed ! So according to this theory
air is much heavier than water, since all heavy
bodies are carried downward more easily through
air than through water, and all light bodies
buoyed up more easily through water than
through air; further there is an infinite number
of heavy bodies which fall through air but
ascend in water and there is an infinite number
of substances which rise in water and fall in
air. But, Simplicio, the question as to whether
the weight of the leather bottle is owing to
thick vapours or to pure air does not affect
our problem which is to discover how bodies
move through this vapour-laden atmosphere
of ours. Returning now to the question which
interests me more, I should like, for the sake
of more complete and thorough knowledge of
this matter, not only to be strengthened in my
belief that air has weight but also to learn, if
possible, how great its specific gravity is. There-
fore, Salviati, if you can satisfy my curiosity on
this point pray do so.
SALV.Theexperimentwith the inflated leather
bottle of Aristotle proves conclusively that air
possesses positive gravity and not, as some have
believed, levity, a property possessed possibly
by no substance whatever; for if air did possess
this quality of absolute and positive levity, it
should on compression exhibit greaterlevityand,
hence, a greater tendency to rise; but experi-
ment shows precisely the opposite.
As to the other question, namely, how to de-
termine the specific gravity of air, I have em-
ployed the following method. I took a rather
large glass bottle with a narrow neck and at-
tached to it a leather cover, binding it tightly
about the neck of the bottle: in the top of this
cover I inserted and firmly fastened the valve of
a leather bottle, through which I forced into
the glass bottle, by means of a syringe, a large
quantity of air. And since air is easily condensed
one can pump into the bottle two or three times
its own volume of air. After this I took an accu-
rate balance and weighed this bottle of com-
pressed air with the utmost precision, adjusting
the weight with fine sand. I next opened the
valve and allowed the compressed air to escape;
then replaced the flask upon the balance and
found it perceptibly lighter : from the sand which
had been used as a counterweight I now re-
moved and laid aside as much as was necessary
to again secure balance. Under these conditions
there can be no doubt but that the weight of
the sand thus laid aside represents the weight of
the air which had been forced into the flask and
had afterwaixfe escaped. But after all this ex-
THE TWO NEW SCIENCES
165
perimcnt tells me merely that the weight of the
compressed air is the same as that of the sand re-
moved from the balance ; when however it comes
to knowing certainly and definitely the weight
of air as compared with that of water or any
other heavy substance, this I cannot hope to do
without first measuring the volume [quantitti] of
compressed air; for this measurement I have de-
vised the two following methods.
According to the first method one takes a bot-
tle with a narrow neck similar to the previous
one; over the mouth of this bottle is slipped a
leather tube which is bound tightly about the
neck of the flask; the other end of this tube em-
braces the valve attached to the first flask and is
tightly bound about it. This second flask is pro-
vided with a hole in the bottom through which
an iron rod can be placed so as to open, at will,
the valve above mentioned and thus permit the
surplus air of the first to escape after it has once
been weighed: but his second bottle must be
filled with water. Having prepared everything
in the manner above described, open the valve
with the rod ; the air will rush into the flask con-
taining the water and will drive it through the
hole at the bottom, it being clear that the vol-
ume of water thus displaced is equal to the vol-
ume of air escaped from the other vessel. Having
set aside this displaced water, weigh the vessel
from which the air has escaped (which is sup-
posed to have been weighed previously while
containing the compressed air), and remove the
surplus of sand as described above; it is then
manifest that the weight of this sand is precisely
the weight of a volume of air equal to the vol-
ume of water displaced and set aside; this water
we can weigh and find how many times its weight
contains the weight of the removed sand, thus
determining definitely how many times heavier
water is than air; and we shall find, contrary to
the opinion of Aristotle, that this is not 10 times,
but, as our experiment shows, more nearly 400
times.
The second method is more expeditious and
can be carried out with a single vessel fitted up
as the first was. Here no air is added to that
which the vessel naturally contains but water is
forced into it without allowing any air to es-
cape ; the water thus introduced necessarily com-
presses the air. Having forced into the vessel as
much water as possible, filing it, say, three-
fourths full, which does not require any extra-
ordinary effort, place it upon the balance and
weigh it accurately; next hold the vessel mouth
up, open the valve, and allow the air to escape;
the volume of the air thus escaping is precisely
equal to the volume of water contained in the
flask. Again weigh the vessel which will have
diminished in weight on account of the escaped
air; this loss in weight represents the weight of a
volume of air equal to the volume of water con-
tained in the vessel.
SIMP. No one can deny the cleverness and in-
genuity of your devices; but while they appear
to give complete intellectual satisfaction they
confuse me in another direction. For since it is
undoubtedly true that the elements when in
their proper places have neither weight nor lev-
ity, I cannot understand how it is possible for
that portion of air, which appeared to weigh,
say, 4 drachms of sand, should really have such
a weight in air as the sand which counterbal-
ances it. It seems to me, therefore, that the ex-
periment should be carried out, not in air, but
in a medium in which the air could exhibit its
property of weight if such it really has.
SALV. The objection of Simplicio is certainly
to the point and must therefore either be un-
answerable or demand an equally clear solution.
It is perfectly evident that that air which, under
compression, weighed as much as the sand, loses
this weight when once allowed to escape into its
own element, while, indeed, the sand retains its
weight. Hence for this experiment it becomes
necessary to select a place where air as well as
sand can gravitate; because, as has been often
remarked, the medium diminishes the weight of
any substance immersed in it by an amount equal
to the weight of the displaced medium; so that
air in air loses all its weight. If therefore this ex-
periment is to be made with accuracy, it should
be performed in a vacuum where every heavy
body exhibits its momentum without the slight-
est diminution. If then, Simplicio, we were to
weigh a portion of air in a vacuum would you
then be satisfied and assured of the fact ?
SIMP. Yes truly : but this is to wish or ask the
impossible.
SALV. Your obligation will then be very great
if, for your sake, I accomplish the impossible.
But I do not want to sell you something which I
have already given you; for in the previous ex-
periment we weighed the air in vacuum and not
in air or other medium. The fact that any fluid
medium diminishes the weight of a mass im-
mersed in it, is due, Simplicio, to the resistance
which this medium offers to its being opened up,
driven aside, and finally lifted up. The evidence
for this is seen in the readiness with which the
fluid rushes to fill up any space formerly occu-
pied by the mass; if the medium were not af-
fected by such an immersion then it would not
i66
GALILEO GALILEI
react against the immersed body. Tell me now,
when you have a flask, in air, rilled with its na-
tural amount of air and then proceed to pump
into the vessel more air, does this extra charge
in any way separate or divide or change the cir-
cumambient air? Does the vessel perhaps ex-
pand so that the surrounding medium is dis-
placed in order to give more room? Certainly
not. Therefore, one is able to say that this extra
charge of air is not immersed in the surrounding
medium for it occupies no space in it, but is, as
it were, in a vacuum. Indeed, it is really in a
vacuum; for it diffuses into the vacuities which
are not completely filled by the original and un-
condensed air. In fact I do not see any differ-
ence between the enclosed and the surrounding
media: for the surrounding medium does not
press upon the enclosed medium, and, vice versa,
the enclosed medium exerts no pressure against
the surrounding one; this same relationship ex-
ists in the case of any matter in a vacuum, as
well as in the case of the extra charge of air com-
pressed into the flask. The weight of this con-
densed air is therefore the same as that which it
would have if set free in a vacuum. It is true of
course that the weight of the sand used as a
counterpoise would be a little greater in vacuo
than in free air. We must, then, say that the air
is slightly lighter than the sand required to
counterbalance it, that is to say, by an amount
equal to the weight in vacuo of a volume of air
equal to the volume of the sand.
At this point in an annotated copy of the original
edition the following note by Galileo is found:
SAGR. A very clever discussion, solving a wonder-
ful problem, because it demonstrates briefly and
concisely the manner in which one may find the
weight of a body in vacuo by simply weighing it in
air. The explanation is as follows: when a heavy
body is immersed in air it loses in weight an amount
equal to the weight of a volume of air equivalent to
the volume of the body itself. Hence if one adds to a
body, without expanding it, a quantity of air equal
to that which it displaces and weighs it, he will ob-
tain its absolute weight in vacuo, since, without in-
creasing it in size, he has increased its weight by just
the amount which it lost through immersion in air.
When, therefore, we force a quantity of water in-
to a vessel which already contains its normal amount
of air, without allowing any of this air to escape it is
clear that this normal quantity of air will be com-
pressed and condensed into a smaller space in order
to make room for the water which is forced in: it is
also clear that the volume of air thus compressed is
eaual to the volume of water added. If now the ves-
sel be weighed in air in this condition, it is manifest
that the weight of the water will be increased by
that of an equal volume of air; the total weight of
water and air thus obtained is equal to the weight
of the water alone in vacuo.
Now record the weight of the entire vessel and
then allow the compressed air to escape; weigh the
remainder; the difference of these two weights will
be the weight of the compressed air which, in vol-
ume, is equal to that of the water. Next find the
weight of the water alone and add to it that of the
compressed air; we shall then have the water alone
in vacuo. To find the weight of the water we shall
have to remove it from the vessel and weigh the ves-
sel alone; subtract this weight from that of the ves-
sel and water together. It is clear that the remainder
will be the weight of the water alone in air.
SIMP. The previous experiments, in my opin-
ion, left something to be desired: but now I am
fully satisfied.
SALV. The facts set forth by me up to this
point and, in particular, the one which shows
that difference of weight, even when very great,
is without effect in changing the speed of falling
bodies, so that as far as weight is concerned they
all fall with equal speed: this idea is, I say, so
new, and at first glance so remote from fact,
that if we do not have the means of making it
just as clear as sunlight, it had better not be
mentioned; but having once allowed it to pass
my lips I must neglect no experiment or argu-
ment to establish it.
SAGR. Not only this but also many other of
your views are so far removed from the com-
monly accepted opinions and doctrines that if
you were to publish them you would stir up a
large number of antagonists; for human nature
is such that men do not look with favor upon
discoveries — either of truth or fallacy—in their
own field, when made by others than themselves.
They call him an innovator of doctrine, an un-
pleasant title, by which they hope to cut those
knots which they cannot untie, and by subter-
ranean mines they seek to destroy structures
which patient artisans have built with custom-
ary tools. But as for ourselves who have no such
thoughts, the experiments and arguments which
you have thus far adduced are fully satisfactory ;
however if you have any experiments which are
more direct or any arguments which are more
convincing, we will hear them with pleasure.
SALV. The experiment made to ascertain
whether two bodies differing greatly in weight
will fall from a given height with the same speed,
offers some difficulty; because, if the height is
considerable, the retarding effect of the medi-
um, which must be penetrated and thrust aside
by the falling body, will be greater in the case of
the small momentum of the very light body
than in the case of the great force of the heavy
THE TWO NEW SCIENCES
167
body; so that, in a long distance, the light body
will be left behind ; if the height be small, one may
well doubt whether there is any difference; and
if there be a difference it will be inappreciable.
It occurred to me, therefore, to repeat many
times the fall through a small height in such a
way that I might accumulate all those small in-
tervals of time that elapse between the arrival
of the heavy and light bodies respectively at
their common terminus, so that this sum makes
an interval of time which is not only observable,
but easily observable. In order to employ the
slowest speeds possible and thus reduce the
change which the resisting medium produces
upon the simple effect of gravity, it occurred to
me to allow the bodies to fall along a plane
slightly inclined to the horizontal. For in such a
plane, just as well as in a vertical plane, one may
discover how bodies of different weight behave:
and besides this, I also wished to rid myself of
the resistance which might arise from contact of
the moving body with the aforesaid inclined
plane. Accordingly, I took two balls, one of lead
and one of cork, the former more than a hun-
dred times heavier than the latter, and suspend-
ed them by means of two equal fine threads,
each four of five cubits long. Pulling each ball
aside from the perpendicular, I let them go at
the same instant, and they, falling along the cir-
cumferences of circles having these equal strings
for semi-diameters, passed beyond the perpen-
dicular and returned along the same path. This
free vibration repeated a hundred times showed
clearly that the heavy body maintains so nearly
the period of the light body that neither in a
hundred swings nor even in a thousand will the
former anticipate the latter by as much as a
single moment, so perfectly do they keep step.
We can also observe the effect of the medium
which, by the resistance which it offers to mo-
tion, diminishes the vibration of the cork more
than that of the lead, but without altering the
frequency of either; even when the arc trav-
ersed by the cork did not exceed five or six de-
grees while that of the lead was fifty or sixty,
the swings were performed in equal times.
SIMP. If this be so, why is not the speed of the
lead greater than that of the cork, seeing that
the former traverses sixty degrees in the same
interval in which the latter covers scarcely six ?
SALV. But what would you say, Simplicio, if
both covered their paths in the same time when
the cork, drawn aside through thirty degrees,
traverses an arc of sixty, while the lead pulled
aside only two degrees traverses an arc of four ?
Would not then the cork be proportionately
swifter? And yet such is the experimental fact.
But observe this: having pulled aside the
pendulum of lead, say through an arc of fifty
degrees, and set it free, it swings beyond the
perpendicular almost fifty degrees, thus de-
scribing an arc of nearly one hundred de-
grees; on the return swing it describes a lit-
tle smaller arc; and after a large number of
such vibrations it finally comes to rest. Each vi-
bration, whether of ninety, fifty, twenty, ten,
or four degrees occupies the same time: accord-
ingly, the speed of the moving body keeps on
diminishing since in equal intervals of time, it
traverses arcs which grow smaller and smaller.
Precisely the same things happen with the
pendulum of cork, suspended by a string of equal
length, except that a smaller number of vibra-
tions is required to bring it to rest, since on ac-
count of its lightness it is less able to overcome
the resistance of the air; nevertheless the vibra-
tions, whether large or small, are all performed
in time-intervals which are not only equal among
themselves, but also equal to the period of the
lead pendulum. Hence it is true that, if while
the lead is traversing an arc of fifty degrees the
cork covers one of only ten, the cork moves
more slowly than the lead; but on the other
hand, it is also true that the cork may cover an
arc of fifty while the lead passes over one of only
ten or six; thus, at different times, we have now
the cork, now the lead, moving more rapidly.
But if these same bodies traverse equal arcs in
equal times we may rest assured that their speeds
are equal.
SIMP. I hesitate to admit the conclusiveness
of this argument because of the confusion which
arises from your making both bodies move now
rapidly, now slowly and now very slowly, which
leaves me in doubt as to whether their velocities
are always equal.
SAGR. Allow me, if you please, Salviati, to say
just a few words. Now tell me, Simplicio, whether
you admit that one can say with certainty that
the speeds of the cork and the lead are equal
whenever both, starting from rest at the same
moment and descending the same slopes, always
traverse equal spaces in equal times ?
SIMP. This can neither be doubted nor gain-
said.
SAGR. Now it happens, in the case of the pen-
dulums, that each of them traverses now an arc
of sixty degrees, now one of fifty, or thirty or
ten or eight or four or two, etc.; and when they
both swing through an arc of sixty degrees they
do so in equal intervals of time; the same thing
happens when the arc is fifty degrees or thirty
i63
GALILEO GALILEI
or ten or any other number; and therefore we
conclude that the speed of the lead in an arc of
sixty degrees is equal to the speed of the cork
when the latter also swings through an arc of
sixty degrees; in the case of a fifty-degree arc
these speeds are also equal to each other; so also
in the case of other arcs. But this is not saying
that the speed which occurs in an arc of sixty is
the same as that which occurs in an arc of fifty;
nor is the speed in an arc of fifty equal to that in
one of thirty, etc.; but the smaller the arcs, the
smaller the speeds; the fact observed is that one
and the same moving body requires the same
time for traversing a large arc of sixty degrees as
for a small arc of fifty or even a very small arc of
ten; all these arcs, indeed, are covered in the
same interval of time. It is true therefore that
the lead and the cork each diminish their speed
in proportion as their arcs diminish; but this
does not contradict the fact that they maintain
equal speeds in equal arcs.
My reason for saying these things has been
rather because I wanted to learn whether I had
correctly understood Salviati, than because I
thought Simplicio had any need of a clearer ex-
planation than that given by Salviati which like
everything else of his is extremely lucid, so lucid,
indeed, that when he solves questions which are
difficult not merely in appearance, but in reality
and in fact, he does so with reasons, observations
and experiments which are common and familiar
to everyone.
In this manner he has, as I have learned from
various sources, given occasion to a highly es-
teemed professor for undervaluing his discover-
ies on the ground that they are commonplace,
and established upon a mean and vulgar basis; as
if it were not a most admirable and praiseworthy
feature of demonstrative science that it springs
from and grows out of principles well-known,
understood, and conceded by all.
But let us continue with this light diet; and
if Simplicio is satisfied to understand and admit
that the gravity inherent in various falling bodies
has nothing to do with the difference of speed
observed among them, and that all bodies, in so
far as their speeds depend upon it, would move
with the same velocity, pray tell us, Salviati,
how you explain the appreciable and evident in-
equality of motion; please reply also to the ob-
jection urged by Simplicio — an objection in
which I concur — namely, that a cannon ball falls
more rapidly than a bird-shot. From my point
of view, one might expect the difference of speed
to be small in the case of bodies of the same sub-
stance moving through any single medium,
whereas the larger ones will descend, during a
single pulse-beat, a distance which the smaller
ones will not traverse in an hour, or in four, or
even in twenty hours; as for instance in the case
of stones and fine sand and especially that very
fine sand which produces muddy water and which
in many hours will not fall through as much as
two cubits, a distance which stones not much
larger will traverse in a single pulse-beat.
SALV. The action of the medium in producing
a greater retardation upon those bodies which
have a less specific gravity has already been ex-
plained by showing that they experience a di-
minution of weight. But to explain how one and
the same medium produces such different re-
tardations in bodies which are made of the same
material and have the same shape, but differ
only in size, requires a discussion more clever
than that by which one explains how a more ex-
panded shape or an opposing motion of the me-
dium retards the speed of the moving body. The
solution of the present problem lies, I think, in
the roughness and porosity which are generally
and almost necessarily found in the surfaces of
solid bodies. When the body is in motion these
rough places strike the air or other ambient me-
dium. The evidence for this is found in the hum-
ming which accompanies the rapid motion of a
body through air, even when that body is as
round as possible. One hears not only humming,
but also hissing and whistling, whenever there
is any appreciable cavity or elevation upon the
body. We observe also that a round solid body
rotating in a lathe produces a current of air. But
what more do we need ? When a top spins on the
ground at its greatest speed do we not hear a dis-
tinct buzzing of high pitch ? This sibilant note
diminishes in pitch as the speed of rotation
slackens, which is evidence that these small ru-
gosities on the surface meet resistance in the air.
There can be no doubt, therefore, that in the
motion of falling bodies these rugosities strike
the surrounding fluid and retard the speed; and
this they do so much the more in proportion as
the surface is larger, which is the case of small
bodies as compared with greater.
SIMP. Stop a moment please, I am getting
confused. For although I understand and admit
that friction of the medium upon the surface of
the body retards its motion and that, if other
things are the same, the larger surface suffers
greater retardation, I do not see on what ground
you say that the surface of the smaller body is
larger. Besides if, as you say, the larger surface
suffers greater retardation the larger solid should
move more slowly, which is not the fact. But
THE TWO NEW SCIENCES
169
this objection can be easily met by saying that,
although the larger body has a larger surface, it
has also a greater weight, in comparison with
which the resistance of the larger surface is no
more than the resistance of the small surface in
comparison with its smaller weight; so that the
speed of the larger solid does not become less. I
therefore see no reason for expecting any differ-
ence of speed, so long as the driving weight di-
minishes in the same proportion as the retard-
ing power of the surface.
SALV. I shall answer all your objections at
once. You will admit, of course, Simplicio, that
if one takes two equal bodies, of the same material
and same figure, bodies which would therefore
fall with equal speeds, and if he diminishes the
weight of one of them in the same proportion as
its surface (maintaining the similarity of shape)
he would not thereby diminish the speed of this
body.
SIMP. This inference seems to be in harmony
with your theory which states that the weight
of a body has no effect in either accelerating or
retarding its motion.
SALV. I quite agree with you in this opinion
from which it appears to follow that, if the weight
of a body is diminished in greater proportion
than its surface, the motion is retarded to a cer-
tain extent; and this retardation is greater and
greater in proportion as the diminution of weight
exceeds that of the surface.
SIMP. This I admit without hesitation.
SALV. Now you must know, Simplicio, that
it is not possible to diminish the surface of a
solid body in the same ratio as the weight, and
at the same time maintain similarity of figure.
For since it is clear that in the case of a diminish-
ing solid the weight grows less in proportion to
the volume, and since the volume always di-
minishes more rapidly than the surface, when
the same shape is maintained, the weight must
therefore diminish more rapidly than the sur-
face. But geometry teaches us that, in the case
of similar solids, the ratio of two volumes is
greater than the ratio of their surfaces; which,
for the sake of better understanding, I shall il-
lustrate by a particular case.
Take, for example, a cube two inches on a
side so that each face has an area of four square
inches and the total area, i.e., the sum of the six
faces, amounts to twenty-four square inches;
now imagine this cube to be sawed through
three times so as to divide it into eight smaller
cubes, each one inch on the side, each face one
inch square, and the total surface of each cube
six square inches instead of twenty-four as in
the case of the larger cube. It is evident there-
fore, that the surface of the little cube is only
one-fourth that of the larger, namely, the ratio
of six to twenty-four; but the volume of the
solid cube itself is only one-eighth; the volume,
and hence also the weight, diminishes therefore
much more rapidly than the surface. If we again
divide the little cube into eight others we shall
have, for the total surface of one of these, one
and one-half square inches, which is one-six-
teenth of the surface of the original cube; but
its volume is only one-sixty-fourth part. Thus,
by two divisions, you see that the volume is
diminished four times as much as the surface.
And, if the subdivision be continued until the
original solid be reduced to a fine powder, we
shall find that the weight of one of these smallest
particles has diminished hundreds and hun-
dreds of times as much as its surface. And this
which I have illustrated in the case of cubes
holds also in the case of all similar solids, where
the volumes stand in sesquialteral ratio to their
surfaces. Observe then how much greater the
resistance, arising from contact of the surface of
the moving body with the medium, in the case
of small bodies than in the case of large; and
when one considers that the rugosities on the
very small surfaces of fine dust particles are per-
haps no smaller than those on the surfaces of
larger solids which have been carefully polished,
he will see how important it is that the medium
should be very fluid and offer no resistance to
being thrust aside, easily yielding to a small
force. You see, therefore, Simplicio, that I was
not mistaken when, not long ago, I said that
the surface of a small solid is comparatively
greater than that of a large one.
SIMP. I am quite convinced; and, believe me,
if I were again beginning my studies, I should
follow the advice of Plato and start with mathe-
matics, a science which proceeds very cautious-
ly and admits nothing as established until it has
been rigidly demonstrated.
SAGR. This discussion has afforded me great
pleasure; but before proceeding further I should
like to hear the explanation of a phrase of yours
which is new to me, namely, that similar solids
are to each other in the sesquialteral ratio of
their surfaces; for although I have seen and un-
derstood the proposition in which it is demon-
strated that the surfaces of similar solids are in
the duplicate ratio of their sides, and also the
proposition which proves that the volumes are
in the triplicate ratio of their sides, yet I have
not so much as heard mentioned the ratio of
the volume of a solid to its surface.
170
GALILEO GALILEI
SALV. You yourself have suggested the an-
swer to your question and have removed every
doubt. For if one quantity is the cube of some-
thing of which another quantity is the square
does it not follow that the cube is the sesqui-
alteral of the square ? Surely. Now if the surface
varies as the square of its linear dimensions while
the volume varies as the cube of these dimen-
sions, may we not say that the volume stands
in sesquialteral ratio to the surface ?
SAGR. Quite so. And now although there are
still some details, in connection with the sub-
ject under discussion, concerning which I might
ask questions yet, if we keep making one digres-
sion after another, it will be long before we
reach the main topic which has to do with the
variety of properties found in the resistance
which solid bodies offer to fracture; and, there-
fore, if you please, let us return to the subject
which we originally proposed to discuss.
SALV. Very well; but the questions which we
have already considered are so numerous and
so varied, and have taken up so much time that
there is not much of this day left to spend upon
our main topic which abounds in geometrical
demonstrations calling for careful consideration.
May I, therefore, suggest that we postpone the
meeting until to-morrow, not only for the rea-
son just mentioned but also in order that I may
bring with me some papers in which I have set
down in an orderly way the theorems and propo-
sitions dealing with the various phases of this
subject, matters which, from memory alone, I
could not present in the proper order.
SAGR. I fully concur in your opinion and all
the more willingly because this will leave time
to-day to take up some of my difficulties with
the subject which we have just been discussing.
One question is whether we are to consider the
resistance of the medium as sufficient to de-
stroy the acceleration of a body of very heavy
material, very large volume, and spherical fig-
ure. I say spherical in order to select a volume
which is contained within a minimum surface
and therefore less subject to retardation.
Another question deals with the vibrations of
pendulums which may be regarded from several
viewpoints; the first is whether all vibrations,
large, medium, and small, are performed in ex-
actly and precisely equal times: another is to
find the ratio of the times of vibration of pen-
dulums supported by threads of unequal length.
SALV. These are interesting questions: but I
fear that here, as in the case of all other facts,
if we take up for discussion any one of them,
it will carry in its wake so many other facts and
curious consequences that time will not remain
to-day for the discussion of all.
SAGR. If these are as full of interest as the fore-
going, I would gladly spend as many days as
there remain hours between now and night-
fall; and I dare say that Simplicio would not be
wearied by these discussions.
SIMP. Certainly not; especially when the
questions pertain to natural science and have
not been treated by other philosophers.
SALV. Now taking up the first question, I can
assert without hesitation that there is no sphere
so large, or composed of material so dense but
that the resistance of the medium, although
very slight, would check its acceleration and
would, in time reduce its motion to uniformity;
a statement which is strongly supported by ex-
periment. For if a falling body, as time goes on,
were to acquire a speed as great as you please,
no such speed, impressed by external forces, can
be so great but that the body will first acquire it
and then, owing to the resisting medium, lose
it. Thus, for instance, if a cannon ball, having
fallen a distance of four cubits through the air
and having acquired a speed of, say, ten units
were to strike the surface of the water, and if
the resistance of the water were not able to
check the momentum of the shot, it would ei-
ther increase in speed or maintain a uniform
motion until the bottom were reached: but
such is not the observed fact; on the contrary,
the water when only a few cubits deep hinders
and diminishes the motion in such a way that
the shot delivers to the bed of the river or lake
a very slight impulse. Clearly then if a short
fall through the water is sufficient to deprive a
cannon ball of its speed, this speed cannot be
regained by a fall of even a thousand cubits.
How could a body acquire, in a fall of a thou-
sand cubits, that which it loses in a fall of four?
But what more is needed ? Do we not observe that
the enormous momentum, delivered to a shot
by a cannon, is so deadened by passing through
a few cubits of water that the ball, so far from
injuring the ship, barely strikes it? Even the
air, although a very yielding medium, can also
diminish the speed of a falling body, as may be
easily understood from similar experiments. For
if a gun be fired downwards from the top of a
very high tower the shot will make a smaller
impression upon the ground than if the gun had
been fired from an elevation of only four or six
cubits; this is clear evidence that the momen-
tum of the ball, fired from the top of the tower,
diminishes continually from the instant it leaves
the barrel until it reaches the ground. There-
THE TWO NEW SCIENCES
171
fore, a fall from ever so great an altitude will
not suffice to give to a body that momentum
which it has once lost through the resistance of
the air, no matter how it was originally ac-
quired. In like manner, the destructive effect
produced upon a wall by a shot fired from a
gun at a distance of twenty cubits cannot be
duplicated by the fall of the same shot from any
altitude however great. My opinion is, there-
fore, that under the circumstances which occur
in nature, the acceleration of any body falling
from rest reaches an end and that the resistance
of the medium finally reduces its speed to a con-
stant value which is thereafter maintained.
SAGR. These experiments are in my opinion
much to the purpose; the only question is
whether an opponent might not make bold to
deny the fact in the case of bodies which are
very large and heavy or to assert that a cannon
ball, falling from the distance of the moon or
from the upper regions of the atmosphere,
would deliver a heavier blow than if just leav-
ing the muzzle of the gun.
SALV. No doubt many objections may be
raised not all of which can be refuted by experi-
ment: however in this particular case the fol-
lowing consideration must be taken into ac-
count, namely, that it is very likely that a heavy
body falling from a height will, on reaching the
ground, have acquired just as much momentum
as was necessary to carry it to that height; as
may be clearly seen in the case of a rather heavy
pendulum which, when pulled aside fifty or six-
ty degrees from the vertical, will acquire pre-
cisely that speed and force which are sufficient
to carry it to an equal elevation, save only that
small portion which it loses through friction on
the air. In order to place a cannon ball at such
a height as might suffice to give it just that
momentum which the powder imparted to it
on leaving the gun, we need only fire it verti-
cally upwards from the same gun; and we can
then observe whether on falling back it delivers
a blow equal to that of the gun fired at close
range; in my opinion it would be much weaker.
The resistance of the air would, therefore, I
think, prevent the muzzle velocity from being
equalled by a natural fall from rest at any height
whatsoever.
We come now to the other questions, relat-
ing to pendulums, a subject which may appear
to many exceedingly arid, especially to those
philosophers who are continually occupied with
the more profound questions of nature. Never-
theless, the problem is one which I do not scorn.
I am encouraged by the example of Aristotle
whom I admire especially because he did not
fail to discuss every subject which he thought
in any degree worthy of consideration.
Impelled by your queries I may give you
some of my ideas concerning certain problems
in music, a splendid subject, upon which so
many eminent men have written: among these
is Aristotle himself who has discussed numer-
ous interesting acoustical questions. According-
ly, if on the basis of some easy and tangible
experiments, I shall explain some striking phe-
nomena in the domain of sound, I trust my ex-
planations will meet your approval.
SAGR. I shall receive them not only grate-
fully but eagerly. For, although I take pleasure
in every kind of musical instrument and have
paid considerable attention to harmony, I have
never been able to fully understand why some
combinations of tones are more pleasing than
others, or why certain combinations not only
fail to please but are even highly offensive. Then
there is the old problem of two stretched strings
in unison; when one of them is sounded, the
other begins to vibrate and to emit its note;
nor do I understand the different ratios of har-
mony and some other details.
SALV. Let us see whether we cannot derive
from the pendulum a satisfactory solution of all
these difficulties. And first, as to the question
whether one and the same pendulum really per-
forms its vibrations, large, medium, and small,
all in exactly the same time, I shall rely upon
what I have already heard from our Academi-
cian. He has clearly shown that the time of de-
scent is the same along all chords, whatever the
arcs which subtend them, as well along an arc of
1 80° (i.e., the whole diameter) as along one of
100°, 60°, 10°, 2°, */2°y or 4'. It is understood, of
course, that these arcs all terminate at the low-
est point of the circle, where it touches the hor-
izontal plane.
If now we consider descent along arcs instead
of their chords then, provided these do not ex-
ceed 90°, experiment shows that they are all
traversed in equal times; but these times are
greater for the chord than for the arc, an effect
which is all the more remarkable because at first
glance one would think just the opposite to be
true. For since the terminal points of the two
motions are the same and since the straight line
included between these two points is the short-
est distance between them, it would seem rea-
sonable that motion along this line should be
executed in the shortest time; but this is not
the case, for the shortest time — and therefore
the most rapid motion — is that employed along
172
GALILEO GALILEI
the arc of which this straight line is the chord.
As to the times of vibration of bodies sus-
pended by threads of different lengths, they
bear to each other the same proportion as the
square roots of the lengths of the thread; or one
might say the lengths are to each other as the
squares of the times; so that if one wishes to
make the vibration- time of one pendulum twice
that of another, he must make its suspension
four times as long. In like manner, if one pendu-
lum has a suspension nine times as long as an-
other, this second pendulum will execute three
vibrations during each one of the first; from
which it follows that the lengths of the suspend-
ing cords bear to each other the [inverse] ratio
of the squares of the number of vibrations per-
formed in the same time.
SAGR. Then, if I understand you correctly, I
can easily measure the length of a string whose
upper end is attached at any height whatever
even if this end were invisible and I could see
only the lower extremity. For if I attach to the
lower end of this string a rather heavy weight
and give it a to-and-fro motion, and if I ask a
friend to count a number of its vibrations, while
I, during the same time-interval, count the
number of vibrations of a pendulum which is
exactly one cubit in length, then knowing the
number of vibrations which each pendulum
makes in the given interval of time one can de-
termine the length of the string. Suppose, for
example, that my friend counts 20 vibrations
of the long cord during the same time in which
I count 240 of my string which is one cubit in
length; taking the squares of the two numbers,
20 and 240, namely 400 and 57600, then, I say,
the long string contains 57600 units of such
length that my pendulum will contain 400 of
them; and since the length of my string is one
cubit, I shall divide 57600 by 400 and thus ob-
tain 144. Accordingly, I shall call the length of
the string 144 cubits.
SALV. Nor will you miss it by as much as a
hand's breadth, especially if you observe a large
number of vibrations.
SAGR. You give me frequent occasion to ad-
mire the wealth and profusion of nature when,
from such common and even trivial phenomena,
you derive facts which are not only striking and
new but which are often far removed from what
we would have imagined. Thousands of times I
have observed vibrations especially in churches
where lamps, suspended by long cords, had been
inadvertently set into motion; but the most
which I could infer from these observations was
that the view of those who think that such vi-
brations are maintained by the medium is high-
ly improbable: for, in that case, the air must
needs have considerable judgment and little
else to do but kill time by pushing to and fro a
pendent weight with perfect regularity. But I
never dreamed of learning that one and the
same body, when suspended from a string a hun-
dred cubits long and pulled aside through an
arc of 90° or even i° or ^°, would employ the
same time in passing through the least as
through the largest of these arcs; and, indeed,
it still strikes me as somewhat unlikely. Now I
am waiting to hear how these same simple
phenomena can furnish solu tions for those acous-
tical problems— solutions which will be at least
partly satisfactory.
SALV. First of all one must observe that each
pendulum has its own time of vibration so defi-
nite and determinate that it is not possible to
make it move with any other period than that
which nature has given it. For let any one take
in his hand the cord to which the weight is at-
tached and try, as much as he pleases, to increase
or diminish the frequency of its vibrations; it
will be time wasted. On the other hand, one
can confer motion upon even a heavy pendulum
which is at rest by simply blowing against it;
by repeating these blasts with a frequency
which is the same as that of the pendulum one
can impart considerable motion. Suppose that
by the first puff we have displaced the pendu-
lum from the vertical by, say, half an inch; then
if, after the pendulum has returned and is about
to begin the second vibration, we add a second
puff, we shall impart additional motion; and so
on with other blasts provided they are applied
at the right instant, and not when the pendulum
is coming toward us, since in this case the blast
would impede rather than aid the motion. Con-
tinuing thus with many impulses we impart to
the pendulum such momentum that a greater
impulse than that of a single blast will be needed
to stop it.
SAGR. Even as a boy, I observed that one man
alone by giving these impulses at the right in-
stant was able to ring a bell so large that when
four, or even six, men seized the rope and tried
to stop it they were lifted from the ground, all
of them together being unable to counterbal-
ance the momentum which a single man, by
properly- timed pulls, had given it.
SALV. Your illustration makes my meaning
clear and is quite as well fitted, as what I have
just said, to explain the wonderful phenomenon
of the strings of the cittern or of the spinet,
namely, the fact that a vibrating string will set
THE TWO NEW SCIENCES
173
another string in motion and cause it to sound
not only when the latter is in unison but even
when it differs from the former by an octave or
a fifth. A string which has been struck begins to
vibrate and continues the motion as long as one
hears the sound; these vibrations cause the im-
mediately surrounding air to vibrate and quiv-
er; then these ripples in the air expand far into
space and strike not only all the strings of the
same instrument but even those of neighboring
instruments. Since that string which is tuned to
unison with the one plucked is capable of vi-
brating with the same frequency, it acquires,
at the first impulse, a slight oscillation; after
receiving two, three, twenty, or more impulses,
delivered at proper intervals, it finally accum-
ulates a vibratory motion equal to that of the
plucked string, as is clearly shown by equality of
amplitude in their vibrations. This undulation
expands through the air and sets into vibration
not only strings, but also any other body which
happens to have the same period as that of the
plucked string. Accordingly if we attach to the
side of an instrument small pieces of bristle or
other flexible bodies, we shall observe that,
when a spinet is sounded, only those pieces re-
spond that have the same period as the string
which has been struck; the remaining pieces do
not vibrate in response to this string, nor do the
former pieces respond to any other tone.
If one bows the base string on a viola rather
smartly and brings near it a goblet of fine, thin
glass having the same tone as that of the string,
this goblet will vibrate and audibly resound.
That the undulations of the medium are widely
dispersed about the sounding body is evinced
by the fact that a glass of water may be made
to emit a tone merely by the friction of the
finger-tip upon the rim of the glass; for in this
water is produced a series of regular waves. The
same phenomenon is observed to better advan-
tage by fixing the base of the goblet upon the
bottom of a rather large vessel of water filled
nearly to the edge of the goblet; for if, as before,
we sound the glass by friction of the finger, we
shall see ripples spreading with the utmost regu-
larity and with high speed to large distances
about the glass. I have often remarked, in thus
sounding a rather large glass nearly full of water,
that at first the waves are spaced with great un-
iformity, and when, as sometimes happens, the
tone of the glass jumps an octave higher I have
noted that at this moment each of the aforesaid
waves divides into two; a phenomenon which
shows clearly that the ratio involved in the oc-
tave is two.
SAGR. More than once have I observed this
same thing, much to my delight and also to my
profit. For a long time I have been perplexed
about these different harmonies, since the ex-
planations hitherto given by those learned in
music impress me as not sufficiently conclusive.
They tell us that the diapason, i.e., the octave,
involves the ratio of two, that the diapente
which we call the fifth involves a ratio of 3 :2,
etc. ; because if the open string of a monochord
be sounded and afterwards a bridge be placed
in the middle and the half length be sounded
one hears the octave; and if the bridge be placed
at y$ the length of the string, then on plucking
first the open string and afterwards ^3 of its
length the fifth is given; for this reason they
say that the octave depends upon the ratio of
two to one and the fifth upon the ratio of three
to two. This explanation does not impress me
as sufficient to establish 2 and 3/2 as the natural
ratios of the octave and the fifth; and my reason
for thinking so is as follows. There are three dif-
ferent ways in which the tone of a string may
be sharpened, namely, by shortening it, by
stretching it, and by making it thinner. If the
tension and size of the string remain constant
one obtains the octave by shortening it to one-
half, i.e., by sounding first the open string and
then one-half of it; but if length and size remain
constant and one attempts to produce the oc-
tave by stretching, he will find that it does not
suffice to double the stretching weight; it must
be quadrupled; so that, if the fundamental note
is produced by a weight of one pound, four will
be required to bring out the octave.
And finally if the length and tension remain
constant, while one changes the size of the
string, he will find that in order to produce the
octave the size must be reduced to 1/4 that
which gave the fundamental. And what I have
said concerning the octave, namely, that its ra-
tio as derived from the tension and size of the
string is the square of that derived from the
length, applies equally well to all other musical
intervals. Thus if one wishes to produce a fifth
by changing the length he finds that the ratio of
the lengths must be sesquialteral, in other words
he sounds first the open string, then two-thirds
of it; but if he wishes to produce this same re-
sult by stretching or thinning the string then it
becomes necessary to square the ratio 3/2 that
is by taking 9/4; accordingly, if the fundamental
requires a weight of 4 pounds, the higher note
will be produced not by 6, but by 9 pounds;
the same is true in regard to size, the string
which gives the fundamental is larger than that
GALILEO GALILEI
which yields the fifth in the ratio of 9 to 4.
In view of these facts, I see no reason why
those wise philosophers should adopt 2 rather
than 4 as the ratio of the octave, or why in the
case of the fifth they should employ the sesqui-
alteral ratio, 3/2, rather than that of 9/4. Since
it is impossible to count the vibrations of a
sounding string on account of its high frequen-
cy, I should still have been in doubt as to
whether a string, emitting the upper octave,
made twice as many vibrations in the same time
as one giving the fundamental, had it not been
for the following fact, namely, that at the in-
stant when the tone jumps to the octave, the
waves which constantly accompany the vibrat-
ing glass divide up into smaller ones which are
precisely half as long as the former.
SALV. This is a beautiful experiment enabling
us to distinguish individually the waves which
are produced by the vibrations of a sonorous
body, which spread through the air, bringing
to the tympanum of the ear a stimulus which
the mind translates into sound. But since these
waves in the water last only so long as the fric-
tion of the finger continues and are, even then,
not constant but are always forming and disap-
pearing, would it not be a fine thing if one had
the ability to produce waves which would per-
sist for a long while, even months and years, so
as to easily measure and count them ?
SAGR. Such an invention would, I assure you,
command my admiration.
SALV. The device is one which I hit upon by
accident; my part consists merely in the obser-
vation of it and in the appreciation of its value
as a confirmation of something to which I had
given profound consideration; and yet the de-
vice is, in itself, rather common. As I was scrap-
ing a brass plate with a sharp iron chisel in or-
der to remove some spots from it and was run-
ning the chisel rather rapidly over it, I once or
twice, during many strokes, heard the plate
emit a rather strong and clear whistling sound;
on looking at the plate more carefully, I noticed
a long row of fine streaks parallel and equidis-
tant from one another. Scraping with the chisel
over and over again, I noticed that it was only
when the plate emitted this hissing noise that
any marks were left upon it; when the scraping
was not accompanied by this sibilant note there
was not the least trace of such marks. Repeat-
ing the trick several times and making the
stroke, now with greater now with less speed,
the whistling followed with a pitch which was
correspondingly higher and lower. I noted also
that the marks made when the tones were
higher were closer together; but when the tones
were deeper, they were farther apart. I also ob-
served that when, during a single stroke, the
speed increased toward the end the sound be-
came sharper and the streaks grew closer to-
gether, but always in such a way as to remain
sharply defined and equidistant. Besides, when-
ever the stroke was accompanied by hissing I
felt the chisel tremble in my grasp and a sort of
shiver run through my hand. In short, we see
and hear in the case of the chisel precisely that
which is seen and heard in the case of a whisper
followed by a loud voice; for, when the breath
is emitted without the production of a tone,
one does not feel either in the throat or mouth
any motion to speak of in comparison with that
which is felt in the larynx and upper part of the
throat when the voice is used, especially when
the tones employed are low and strong.
At times I have also observed among the
strings of the spinet two which were in unison
with two of the tones produced by the afore-
said scraping; and among those which differed
most in pitch I found two which were separated
by an interval of a perfect fifth. Upon measur-
ing the distance between the markings pro-
duced by the two scrapings it was found that
the space which contained 45 of one contained
30 of the other, which is precisely the ratio as-
signed to the fifth.
But now, before proceeding any farther, I
want to call your attention to the fact that, of
the three methods for sharpening a tone, the
one which you refer to as the fineness of the
string should be attributed to its weight. So
long as the material of the string is unchanged,
the size and weight vary in the same ratio. Thus
in the case of gut-strings, we obtain the octave
by making one string 4 times as large as the
other; so also in the case of brass one wire must
have 4 times the size of the other; but if now we
wish to obtain the octave of a gut-string, by
use of brass wire, we must make it, not four
times as large, but four times as heavy as the
gut-string: as regards size, therefore, the metal
string is not four times as big but four times as
heavy. The wire may therefore be even thinner
than the gut, notwithstanding the fact that the
latter gives the higher note. Hence if two spin-
ets are strung, one with gold wire the other
with brass, and if the corresponding strings each
have the same length, diameter, and tension, it
follows that the instrument strung with gold
will have a pitch about one-fifth lower than the
other because gold has a density almost twice
that of brass. And here it is to be noted that it
THE TWO NEW SCIENCES
'75
is the weight rather than the size of a moving
body which offers resistance to change of mo-
tion, contrary to what one might at first glance
think. For it seems reasonable to believe that
a body which is large and light should suffer
greater retardation of motion in thrusting aside
the medium than would one which is thin and
heavy, yet here exactly the opposite is true.
Returning now to the original subject of dis-
cussion, I assert that the ratio of a musical in-
terval is not immediately determined either by
the length, size, or tension of the strings but
rather by the ratio of their frequencies, that is,
by the number of pulses of air waves which
strike the tympanum of the ear, causing it also
to vibrate with the same frequency. This fact
established, we may possibly explain why cer-
tain pairs of notes, differing in pitch produce a
pleasing sensation, others a less pleasant effect,
and still others a disagreeable sensation. Such
an explanation would be tantamount to an ex-
planation of the more or less perfect consonances
and of dissonances. The unpleasant sensation
produced by the latter arises, I think, from the
discordant vibrations of two different tones
which strike the ear out of time. Especially
harsh is the dissonance between notes whose fre-
quencies are incommensurable; such a case oc-
curs when one has two strings in unison and
sounds one of them open, together with a part
of the other which bears the same ratio to its
whole length, as the side of a square bears to
the diagonal; this yields a dissonance similar
to the augmented fourth or diminished fifth.
Agreeable consonances are pairs of tones
which strike the ear with a certain regularity;
this regularity consists in the fact that the puls-
es delivered by the two tones, in the same inter-
val of time, shall be commensurable in number,
so as not to keep the ear drum in perpetual
torment, bending in two different directions in
order to yield to the ever-discordant impulses.
The first and most pleasing consonance is,
therefore, the octave since, for every pulse
given to the tympanum by the lower string,
the sharp string delivers two; accordingly, at
every other vibration of the upper string, both
pulses are delivered simultaneously so that one-
half the entire number of pulses are delivered
in unison. But when two strings are in unison
their vibrations always coincide and the effect
is that of a single string; hence we do not refer
to it as consonance. The fifth is also a pleasing
interval since for every two vibrations of the
lower string the upper one gives three, so that
considering the entire number of pulses from
the upper string one-third of them will strike in
unison, i.c.y between each pair of concordant
vibrations there intervene two single vibra-
tions; and when the interval is a fourth, three
single vibrations intervene. In case the interval
is a second where the ratio is 9/8 it is only every
ninth vibration of the upper string which
reaches the ear simultaneously with one of the
lower; all the others are discordant and produce
a harsh effect upon the recipient ear which in-
terprets them as dissonances.
SIMP. Won't you be good enough to explain
this argument a little more clearly?
SALV. Let AB denote the length of a wave
emitted by the lower string and CD that of a
higher string which is emitting the octave ofAB;
divide AB in the middle at E. If the two strings
begin their motions at A and C, it is clear that
when the sharp vibration has reached the end
Z), the other vibration will have travelled
only as far as E, which, not being a terminal
point, will emit no pulse; but there is a blow de-
livered at D. Accordingly, when the one wave
comes back from D to C, the other passes on
from E to B; hence the two pulses from B and
C strike the drum of the ear simultaneously
Seeing that these vibrations are repeated again
A E B and again in the same
manner, we conclude that
£ P each alternate pulse from
1 ' CD falls in unison with
one from AB. But each of
A E Q B *ke pulsations at the ter-
1 ' ~ minal points, A and By is
Q _ constantly accompanied
1 £: * by one which leaves al-
^lg- 13 ways from C or always
from D. This is clear because if we suppose the
waves to reach A and C at the same instant,
then, while one wave travels from A to 5, the
other will proceed from CtoD and back to C,
so that waves strike at C and B simultaneously;
during the passage of the wave from B back to
A the disturbance at Cgoes to D and again re-
turns to C, so that once more the pulses at A
and C are simultaneous.
Next let the vibrations AB and CD be separa-
ted by an interval of a fifth, that is, by a ratio of
3/2; choose the points E and O such that they
will divide the wave length of the lower string
into three equal parts and imagine the vibra-
tions to start at the same instant from each of
the terminals A and C It is evident that when
the pulse has been delivered at the terminal Z),
the wave in AB has travelled only as far as 0;
the drum of the ear receives, therefore, only the
i76
GALILEO GALILEI
pulse from D. Then during the return of the
one vibration from D to C, the other will pass
from O to B and then back to O, producing an
isolated pulse at 5— a pulse which is out of
time but one which must be taken into con-
sideration.
Now since we have assumed that the first
pulsations started from the terminals A and G
at the same instant, it follows that the second
pulsation, isolated at D, occurred after an in-
terval of time equal to that required for passage
from C to D or, what is the same thing, from A
to O; but the next pulsation, the one at B, is
separated from the preceding by only half this
interval, namely, the time required for passage
from 0 to B. Next while the one vibration
travels from O to A, the other travels from C to
Z), the result of which is that two pulsations oc-
cur simultaneously at A and D. Cycles of this
kind follow one after another, i.e., one solitary
pulse of the lower string interposed between
two solitary pulses of the upper string. Let us
now imagine time to be divided into very small
equal intervals; then if we assume that, during
the first two of these intervals, the disturbances
which occurred simultaneously at A and C have
travelled as far as 0 and D and have produced
a pulse at D; and if we assume that during the
third and fourth intervals one disturbance re-
turns from D to C, producing a pulse at C,
while the other, passing on from O to B and
back to O, produces a pulse at B; and if finally,
during the fifth and sixth intervals, the disturb-
ances travel from O and C to A and D, pro-
ducing a pulse at each of the latter two, then
the sequence in which the pulses strike the ear
will be such that, if we begin to count time
from any instant where two pulses are simul-
taneous, the ear drum will, after the lapse of
two of the said intervals, receive a solitary
pulse; at the end of the third interval, another
solitary pulse; so also at the end of the fourth
interval; and two intervals later, i.e., at the end
of the sixth interval, will be heard two pulses in
unison. Here ends the cycle — the anomaly, so
to speak— which repeats itself over and over
again.
SAGR. I can no longer remain silent; for I
must express to you the great pleasure I have
in hearing such a complete explanation of phe-
nomena with regard to which I have so long
been in darkness. Now I understand why unison
does not differ from a single tone; I understand
why the octave is the principal harmony, but
so like unison as often to be mistaken for it and
also why it occurs with the other harmonies. It
resembles unison because the pulsations of
strings in unison always occur simultaneously,
and those of the lower string of the octave are
always accompanied by those of the upper
string; and among the latter is interposed a soli-
tary pulse at equal intervals and in such a man-
ner as to produce no disturbance; the result is
that such a harmony is rather too much soft-
ened and lacks fire. But the fifth is character-
ized by its displaced beats and by the inter-
position of two solitary beats of the upper
string and one solitary beat of the lower string
between each pair of simultaneous pulses; these
three solitary pulses are separated by intervals
of time equal to half the interval which sepa-
rates each pair of simultaneous beats from the
solitary beats of the upper string. Thus the ef-
fect of the fifth is to produce a tickling of the
ear drum such that its softness is modified with
sprightliness, giving at the same moment the
impression of a gentle kiss and of a bite.
SALV. Seeing that you have derived so much
pleasure from these novelties, I must show you
a method by which the eye may enjoy the same
game as the ear. Suspend three balls of lead, or
other heavy material, by means of strings of dif-
ferent length such that while the longest makes
two vibrations the shortest will make four and
the medium three; this will take place when the
longest string measures 16, either in hand
breadths or in any other unit, the medium 9
and the shortest 4, all measured in the same unit.
Now pull all these pendulums aside from the
perpendicular and release them at the same in-
stant; you will see a curious interplay of the
threads passing each other in various manners
but such that at the completion of every fourth
vibration of the longest pendulum, all three will
arrive simultaneously at the same terminus,
whence they start over again to repeat the same
cycle. This combination of vibrations, when pro-
duced on strings is precisely that which yields
the interval of the octave and the intermediate
fifth. If we employ the same disposition of ap-
paratus but change the lengths of the threads,
always however, in such a way that their vibra-
tions correspond to those of agreeable musical
intervals, we shall see a different crossing of these
threads but always such that, after a definite
interval of time and after a definite number of
vibrations, all the threads, whether three or four,
will reach the same terminus at the same in-
stant, and then begin a repetition of the cycle.
If however the vibrations of two or more
strings are incommensurable so that they
never complete a definite number of vibrations
THE TWO NEW SCIENCES
177
at the same instant, or if commensurable they
return only after a long interval of time and
after a large number of vibrations, then the
eye is confused by the disorderly succession of
crossed threads. In like manner the ear is
pained by an irregular sequence of air waves
which strike the tympanum without any fixed
order.
But, gentlemen, whither have we drifted dur-
ing these many hours lured on by various prob-
lems and unexpected digressions ? The day is al-
ready ended and we have scarcely touched the
subject proposed for discussion. Indeed we have
deviated so far that I remember only with diffi-
culty our early introduction and the little prog-
ress made in the way of hypotheses and princi-
ples for use in later demonstrations.
SAGR. Let us then adjourn for to-day in order
that our minds may find refreshment in sleep and
that we may return tomorrow, if so please you,
and resume the discussion of the main question.
SALV. I shall not fail to be here to-morrow at
the same hour, hoping not only to render you
service but also to enjoy your company.
SECOND DAY
SAGREDO. While Simplicio and I were awaiting
your arrival we were trying to recall that last
consideration which you advanced as a principle
and basis for the results you intended to obtain;
this consideration dealt with the resistance which
all solids offer to fracture and depended upon a
certain cement which held the parts glued to-
gether so that they would yield and separate
only under considerable pull. Later we tried to
find the explanation of this coherence, seeking
it mainly in the vacuum; this was the occasion
of our many digressions which occupied the en-
tire day and led us far afield from the original
question which, as I have already stated, was
the consideration of the resistance that solids
offer to fracture.
SALV. I remember it all very well. Resuming
the thread of our discourse, whatever the nature
of this resistance which solids offer to large trac-
tive forces there can at least be no doubt of its
existence ; and though this resistance is very great
in the case of a direct pull, it is found, as a rule,
to be less in the case of bending forces. Thus, for
example, a rod of steel or of glass will sustain a
longitudinal pull of a thousand pounds while a
weight of fifty pounds would be quite sufficient
to break it if the rod were fastened at right angles
into a vertical wall. It is this second type of re-
sistance which we must consider, seeking to dis-
cover in what proportion it is found in prisms
and cylinders of the same material, whether
alike or unlike in shape, length, and thickness.
In this discussion I shall take for granted the
well-known mechanical principle which has been
shown to govern the behaviour of a bar, which
we call a lever, namely, that the force bears to
the resistance the inverse ratio of the distances
which separate the fulcrum from the force and
resistance respectively.
SIMP. This was demonstrated first of all by
Aristotle, in his Mechanics.
SALV. Yes, I am willing to concede him prior-
ity in point of time; but as regards rigour of dem-
onstration the first place must be given to Arch-
imedes, since upon a single proposition proved
in his book on Equilibrium1 depends not only
1 See Archimedes, Equilibrium of Planes, p. 502-19.
the law of the lever but also those of most other
mechanical devices.
SAGR. Since now this principle is fundamental
to all the demonstrations which you propose to
set forth would it not be advisable to give us a
complete and thorough proof of this proposi-
tion, unless possibly it would take too much time ?
SALV. Yes, that would be quite proper, but it
is better I think to approach our subject in a
manner somewhat different from that employed
by Archimedes, namely, by first assuming mere-
ly that equal weights placed in a balance of equal
arms will produce equilibrium— a principle also
assumed by Archimedes — and then proving that
it is no less true that unequal weights produce
equilibrium when the arms of the steelyard have
lengths inversely proportional to the weights
suspended from them ; in other words, it amounts
to the same thing whether one places equal
weights at equal distances or unequal weights at
distances which bear to each other the inverse
ratio of the weights.
In order to make this matter clear imagine a
prism or solid cylinder, AB, suspended at each
end to the rod ///, and supported by two
threads HA and IB; it is evident that if I attach
a thread, C, at the middle point of the balance
beam HI, the entire prism AB will, according
to the principle assumed, hang in equilibrium
since one-half its weight lies on one side, and the
other half on the other side, of the point of sus-
pension C. Now suppose the prism to be divid-
ed into unequal parts by a plane through the
line D, and let the part DA be the larger and
DB the smaller: this division having been made,
imagine a thread ED, attached at the point E
and supporting the parts AD and DB, in order
that these parts may remain in the same posi-
tion relative to line HI: and since the relative
position of the prism and the beam HI remains
unchanged, there can be no doubt but that the
prism will maintain its former state of equili-
brium. But circumstances would remain the
same if that part of the prism which is now held
up, at the ends, by the threads AH and DE
were supported at the middle by a single thread
GL; and likewise the other part DB would not
THE TWO NEW SCIENCES
179
H
Fig. 14
change position if held by a thread FM placed
at its middle point. Suppose now the threads
HA, ED, and IB to be removed, leaving only
the two GL and FM, then the same equilibrium
will be maintained so long as the suspension is
at C. Now let us consider that we have here
two heavy bodies AD and DB hung at the ends
G and F, of a balance beam GF in equilibrium
about the point C, so that the line CG is the
distance from G to the point of suspension of
the heavy body AD, while CF is the distance
at which the other heavy body, DB, is sup-
ported. It remains now only to show that these
distances bear to each other the inverse ratio of
the weights themselves, that is, the distance GC
is to the distance CF as the prism DB is to the
prism DA— a proposition which we shall prove
as follows: Since the line GE is the half of EH,
and since EF is the half of El, the whole length
GF will be half of the entire line HI, and there-
fore equal to CI\ if now we subtract the com-
mon part CF the remainder GC will be equal
to the remainder Fl, that is, to FE, and if to
each of these we add CE we shall have GE
equal to CF: hence GE:EF=FC:CG. But GE
and EF bear the same ratio
to each other as do their
doubles HE and El, that is,
the same ratio as the prism
AD to DB. Therefore, by
equating ratios we have,
convertendo, the distance
GC is to the distance CF
as the weight BD is to the
weight DA, which is what I desired to prove.
If what precedes is clear, you will not hesi-
tate, I think, to admit that the two prisms AD
and DB are in equilibrium about the point C
since one-half of the whole body AB lies on the
right of the suspension C and the other half on
the left; in other words, this arrangement is
equivalent to two equal weights disposed at
equal distances. I do not see how any one can
doubt, if the two prisms AD and DB were trans-
formed into cubes, spheres, or into any other
figure whatever and if G and F were
retained as points of suspension, that
they would remain in equilibrium a-
bout the point C, for it is only too
evident that change of figure does
not produce change of weight so long
as the mass does not vary. From this
we may derive the general conclusion
that any two heavy bodies are in
equilibrium at distances which are in-
versely proportional to their weights.
This principle established, I desire, before
passing to any other subject, to call your atten-
tion to the fact that these forces, resistances,
moments, figures, etc., may be considered either
in the abstract, dissociated from matter, or in
the concrete, associated with matter. Hence
the properties which belong to figures that are
merely geometrical and non-material must be
modified when we fill these figures with matter
and therefore give them weight. Take, for ex-
ample, the lever BA which, resting upon the
support E, is used to lift a heavy stone D. The
principle just demonstrated makes it clear that
a force applied at the extremity B will just suf-
fice to equilibrate the resistance offered by the
heavy body D, provided this force bears to the
force at D the same ratio as the distance AC
bears to the distance CB\ and this is true so long
as we consider only the moments of the single
force at B and of the resistance at D, treating
the lever as an immaterial body devoid of
weight. But if we take into account the weight
of the lever itself— an instrument which may
be made either of wood or of iron — it is mani-
fest that, when this weight has been added to
B
Fig. 15
the force at B, the ratio will be changed and
must therefore be expressed in different terms.
Hence, before going further let us agree to dis-
tinguish between these two points of view;
when we consider an instrument in the abstract,
i.e., apart from the weight of its own material,
we shall speak of "taking it in an absolute
sense"; but if we fill one of these simple and
absolute figures with matter and thus give it
weight, we shall refer to such a material figure
as a "moment" or "compound force."
i8o
GALILEO GALILEI
SAGR. I must break my resolution about not
leading you off into a digression; for I cannot
concentrate my attention upon what is to fol-
low until a certain doubt is removed from my
mind, namely, you seem to compare the force
at B with the total weight of the stone D, a
part of which — possibly the greater part— rests
upon the horizontal plane: so that . . .
SALV. I understand perfectly: you need go
no further. However, please observe that I have
not mentioned the total weight of the stone;
I spoke only of its force at the point A,
the extremity of the lever BA, which force is
always less than the total weight of the stone,
and varies with its shape and elevation.
SAGR. Good: but there occurs to me another
question about which I am curious. For a com-
plete understanding of this matter, 1 should like
you to show me, if possible, how one can deter-
mine what part of the total weight is supported
by the underlying plane and what part by the
end A of the lever.
SALV. The explanation will not delay us long
and I shall therefore have pleasure in granting
your request. In the accompanying figure, let us
understand that the weight having its center of
gravity at A rests with the end B upon the hori-
zontal plane and with the other end upon the
lever CG. Let N be the fulcrum of a lever to
which the force is applied at G. Let fall the per-
pendiculars, AO and CF, from the center A and
the end C. Then I say, the magnitude of the en-
tire weight bears to the magnitude of the force
at G a ratio compounded of the ratio between
the two distances GN and NC and the ratio be-
Fig. 16
tween FB and BO. Lay off a distance X such
that its ratio to NC is the same as that of BO to
FB; then, since the total weight A is counter-
balanced by the two forces at B and at C, it fol-
lows that the force at B is to that at Cas the dis-
tance FO is to the distance OB. Hence, com-
ponendo, the sum of the forces at B and C, that
is, the total weight A, is to the force at Cas the
line FB is to the line BO, that is, as NC is to X:
but the force applied at C is to the force applied
at G as the distance GN is to the distance NC;
hence it follows, ex aequali in proportione pertur-
bata? that the entire weight A is to the force ap-
plied at G as the distance GN is to X. But the
ratio of GN to X is compounded of the ratio of
GW to WC and of WC to X, that is, of FB to BO;
hence the weight A bears to the equilibrating
force at G a ratio compounded of that of GN to
NCand of FB to BO: which was to be proved.
Let us now return to our original subject;
then, if what has hitherto been said is clear, it
will be easily understood that,
PROPOSITION I
A prism or solid cylinder of glass, steel, wood,
or other breakable material which is capable of
sustaining a very heavy weight when applied
longitudinally is, as previously remarked, easily
broken by the transverse application of a weight
which may be much smaller in proportion as the
length of the cylinder exceeds its thickness.
Let us imagine a solid prism ABCD fastened
into a wall at the end AB, and supporting a
weight £ at the other end; understand also that
the wall is vertical and that the prism or cylin-
der is fastened at right angles to the wail. It is clear
that, if the cylinder breaks, fracture will occur
at the point B where the edge of the mortise
acts as a fulcrum for the lever BC, to which the
force is applied; the thickness of the solid BA is
the other arm of the lever along which is located
the resistance. This resistance opposes the sep-
aration of the part BD, lying outside the wall,
from that portion lying inside. From the pre-
ceding, it follows that the magnitude of the force
applied at C bears to the magnitude of the re-
sistance, found in the thickness of the prism, i.
e., in the attachment of the base BA
to its contiguous parts, the same
'G ratio which the length CB bears to
half the length BA; if now we define
absolute resistance to fracture as that
offered to a longitudinal pull (in
which case the stretching force acts
in the same direction as that
through which the body is moved),
then it follows that the absolute resistance of
the prism BD is to the breaking load placed at
the end of the lever EC in the same ratio as the
length EC is to the half of AB in the case of a
prism, or the semidiameter in the case of a cyl-
inder. This is our first proposition. Observe
that in what has here been said the weight of
the solid BD itself has been left out of consider-
ation, or rather, the prism has been assumed to
be devoid of weight. But if the weight of the
prism is to be taken account of in conjunction
1 See Euclid, v. 20.
THE TWO NEW SCIENCES
181
SALV. Precisely so, and a fact worth
remembering. Now we can readily un-
derstand
PROPOSITION II
How and in what proportion a rod,
or rather a prism, whose width is great-
er than its thickness offers more resis-
Fig. 17
with the weight E, we must add to the weight
E one half that of the prism BD: so that if, for
example, the latter weighs two pounds and the
weight E is ten pounds we must treat the
weight E as if it were eleven pounds.
SIMP. Why not twelve ?
SALV. The weight E, my dear Simplicio, hang-
ing at the extreme end Cacts upon the lever EC
with its full moment often pounds: so also would
the solid BD if suspended at the same point ex-
ert its full moment of two pounds; but, as you
know, this solid isuniformly distributed through-
out its entire length, BC, so that the parts which
lie near the end B are less effective than those
more remote.
Accordingly, if we strike a balance between
the two, the weight of the entire prism may be
considered as concentrated at its center of grav-
ity which lies midway of the lever BC. But a
weight hung at the extremity C exerts a mo-
ment twice as great as it would if suspended from
the middle: therefore, if we consider the mo-
ments of both as located at the end C, we must
add to the weight E one-half that of the prism.
SIMP. I understand perfectly; and moreover,
if I mistake not, the force of the two weights
BD and E, thus disposed, would exert the same
moment as would the entire weight BD together
with twice the weight E suspended at the mid-
dle of the lever BC,
Fig. 18
tance to fracture when the force is applied in
the direction of its breadth than in the direction
of its thickness.
For the sake of clearness, take a ruler ad whose
width is acand whose thickness, cb, is much less
than its width. The question now is why will
the ruler, if stood on edge, as in the first figure,
withstand a great weight T, while, when laid
flat, as in the second figure, it will not support
the weight X which is less than T. The answer is
evident when we remember that in the one case
the fulcrum is at the line be, and in the other case
at ca , while the distance at which the force is ap-
plied is the same in both cases, namely, the length
bd but in the first case the distance of the re-
sistance from the fulcrum — half the line ca— is
greater than in the other case where it is only
half of be. Therefore the weight Tis greater than
X in the same ratio as half the width ca is greater
than half the thickness be, since the former acts
as a lever arm for ca, and the latter for cb, against
the same resistance, namely, the strength of all
the fibres in the cross-section ab. We conclude,
therefore, that any given ruler, or prism, whose
width exceeds its thickness, will offer greater re-
sistance to fracture when standing on edge than
182
GALILEO GALILEI
when lying flat, and this in the ratio of the width
to the thickness.
PROPOSITION III
Considering now the case of a prism or cyl-
inder growing longer in a horizontal direction,
we must find out in what ratio the moment of
its own weight increases in comparison with its
resistance to fracture. This moment I find in-
creases in proportion to the square of the length.
In order to prove this let AD be a prism or cyl-
inder lying horizontal with its end A firmly fixed
in a wall. Let the length of the prism be increased
by the addition of the portion BE. It is clear
that merely changing the length of the lever
from AB to AC will, if we disregard its weight,
increase the moment of the force tending to
produce fracture at A in the ratio of CA to BA.
But, besides this, the weight of the solid portion
BE, added to the weight of the solid AB in-
creases the moment of the total weight in the
ratio of the weight of the prism AE to that of
the prism AB, which is the same as the ratio of
the length AC to AB.
It follows, therefore, that, when the length
and weight are simultaneously increased in any
given proportion, the moment, which is the
product of these two, is increased in a ratio which
is the square of the preceding proportion. The
conclusion is then that the bending moments
due to the weight of prisms and cylinders which
have the same thickness but different lengths,
Fig. 19
bear to each other a ratio which is the square of
the ratio of their lengths, or, what is the same
thing, the ratio of the squares of their lengths.
We shall next show in what ratio the resist-
ance to fracture, in prisms and cylinders, in-
creases with increase of thickness while the
length remains unchanged. Here I say that
PROPOSITION IV
In prisms and cylinders of equal length, but of un-
equal thicknesses , the resistance to fracture increases
in the same ratio as the cube of the diameter of the
thickness, i. e., of the base.
Let A and B be two cylinders of equal lengths
DG, FH; let their bases be circular but unequal,
having the diameters CD and EF. Then I say
that the resistance to fracture offered by the
cylinder B is to that offered by A as the cube of
the diameter FE is to the cube of the diameter
DC. For, if we consider the resistance to frac-
ture by longitudinal pull as dependent upon the
bases, i.e., upon the circles EF and DC, no one
can doubt that the strength of the cylinder B is
greater than that of A in the same proportion in
which the area of the circle EF exceeds that of
CD; because it is precisely in this ratio that the
number of fibres binding the parts of the solid
together in the one cylinder exceeds that in the
other cylinder.
But in the case of a force acting transversely
it must be remembered that we are employing
two levers in which the forces are applied at
distances DG, FH, and the ful-
crums are located at the points
D and F; but the resistances are
applied at distances which are
equal to the radii of the circles
DC and EF, since the fibres dis-
tributed over these entire cross-
sections act as if concentrated at
the centres. Remembering this
and remembering also that the
arms, DG and FH, through
which the forces G and //act
are equal, we can understand
that the resistance, located at the
centre of the base EF, acting
against the force at H, is more
effective than the resistance at
the centre of the base CD op-
posing the force G, in the ratio
of the radius FE to the radius
DC. Accordingly, the resistance
to fracture offered by the cylin-
der B is greater than that of the
cylinder A in a ratio which is
THE TWO NEW SCIENCES
183
Fig. 20
compounded of that of the area of the circles
EF and DC and that of their radii, i.e., of their
diameters; but the areas of circles are as the
squares of their diameters. Therefore the ratio
of the resistances, being the product of the two
preceding ratios, is the same as that of the cubes
of the diameters. This is what I set out to prove.
Also since the volume of a cube varies as the
third power of its edge we may say that the re-
sistance [strength] of a cylinder whose length
remains constant varies as the third power of
its diameter.
From the preceding we are able to conclude
that -
COROLLARY
The resistance of a prism or cylinder of con-
stant length varies in the sesquialteral ratio of
its volume.
This is evident because the volume of a prism
or cylinder of constant altitude varies directly
as the area of its base, />., as the square of a
side or diameter of this base; but, as just demon-
strated, the resistance varies as the cube of this
same side or diameter. Hence the resistance
varies in the sesquialteral ratio of the volume —
consequently also of the weight — of the solid
itself.
SIMP. Before proceeding further I should like
to have one of my difficulties removed. Up to
this point you have not taken into considera-
tion a certain other kind of resistance which, it
appears to me, diminishes as the solid grows
longer, and this is quite as true in the case of
bending as in pulling; it is precisely thus that
in the case of a rope we observe that a very long
one is less able to support a large weight than a
short one. Whence, I believe, a short rod of
wood or iron will support a greater weight than
if it were long, provided the force be always ap-
plied longitudinally and not transversely, and
provided also that we take into account the
weight of the rope itself which increases with
its length.
SALV, I fear, Simplicio, if I correctly catch
your meaning, that in this particular you are
making the same mistake as many others; that
is if you mean to say that a long rope, one of
perhaps 40 cubits, cannot hold up so great a
weight as a shorter length, say one or two cu-
bits, of the same rope.
SIMP. That is what I meant, and as far as I
see the proposition is highly probable.
SALV. On the contrary, I consider it not
merely improbable but false; and I think I can
easily convince you of your error. Let AB rep-
resent the rope, fastened at the upper end A : at
the lower end attach a weight C whose force is
just sufficient to break the rope. Now, Simpli-
cio, point out the exact place where you think
the break ought to occur.
SIMP. Let us say D.
SALV. And why at Z>?
SIMP. Because at this point the rope is not
strong enough to support, say, 100 poundsy
made up of the portion of the rope DB and the
stone C.
SALV. Accordingly, whenever the rope is
stretched with the weight of 100 pounds at D
it will break there.
SIMP. I think so.
SALV. But tell me, if instead of attaching the
weight at the end of the rope, 5,
one fastens it at a point nearer D,
say, at E: or if, instead of fixing
the upper end of the rope at A,
one fastens it at some point F,
just above D, will not the rope,
at the point D, be subject to the
same pull of 100 pounds?
SIMP. It would, provided you
include with the stone C the por-
tion of rope EB.
SALV. Let us therefore suppose
that the rope is stretched at the
point D with a weight of 100
pounds, then according to your
own admission it will break; but
FE is only a small portion ofAB;
how can you therefore maintain
that the long rope is weaker than
the short one ? Give up then this
erroneous view which you share
with many very intelligent peo-
ple, and let us proceed.
Now having demonstrated that, in the case
of prisms and cylinders of constant thickness,
the moment of force tending to produce frac-
ture varies as the square of the length; and hav-
ing likewise shown that, when the length is con-
stant and the thickness varies, the resistance to
Fig. 21
1 84
GALILEO GALILEI
fracture varies as the cube of the side, or di-
ameter, of the base, let us pass to the investiga-
tion of the case of solids which simultaneously
vary in both length and thickness. Here I ob-
serve that, .. _.
PROPOSITION V
Prisms and cylinders which differ in both length
and thickness offer resistances to fracture which
are directly proportional to the cubes of the di-
ameters of their bases and inversely proportional
to their lengths.
Let ABC and DEF be two such cylinders;
then the resistance of the cylinder AC bears to
the resistance of the cylinder DFa ratio which
is the product of the cube of the diameter AB
divided by the cube of the diameter DE, and of
A
let us next consider the case of prisms and cyl-
inders which are similar. Concerning these we
shall show that,
PROPOSITION VI
In the case of similar cylinders and prisms, the
moments [stretching forces] which result from
multiplying together their weight and length [i.e.
from the moments produced by their own weight
and length], which latter acts as a lever-arm, bear
to each other a ratio which is the sesquialteral of
the ratio between the resistances of their bases.
In order to prove this let us indicate the two
similar cylinders by AB and CD: then the mag-
nitude of the force in the cylinder AB, oppos-
ing the resistance of its base B, bears to the
magnitude of the force at CD, opposing the re-
sistance of its base D, a ratio which is the ses-
quialteral of the ratio between the resistance of
the base B and the resistance of the base D. And
Fig. 22
the length EF divided by the length BC. Make
EG equal to BC: let 77 be a third proportional
to the lines AB and DE', let I be a fourth pro-
portional, [AB/DE=H/I]: and let 7:5 =
EF:BC.
Now since the resistance of the cylinder AC
is to that of the cylinder DG as the cube of AB
is to the cube of DE, that is, as the length AB
is to the length I ; and since the resistance of the
cylinder DG is to that of the cylinder DF as
the length FE is to EG, that is, as 7 is to S, it fol-
lows that the length AB is to S as the resistance
of the cylinder A C is to that of the cylinder DF.
But the line AB bears to S a ratio which is the
product of AB/ 1 and 7/5. Hence the resistance
of the cylinder AC bears to the resistance of the
cylinder DF a ratio which is the product of
AB/I (that is, Affl /DP) and of 7/5 (that is,
EF/BC) : which is what I meant to prove.
This proposition having been demonstrated,
Fig. 23
since the solids AB and CD, are effective in op-
posing the resistances of their bases B and D,
in proportion to their weights and to the me-
chanical advantages of their lever arms respec-
tively, and since the advantage of the lever
arm AB is equal to the advantage of the lever
arm CD (this is true because in virtue of the
similarity of the cylinders the length AB is to
the radius of the base B as the length CD is to
the radius of the base Z)), it follows that the
total force of the cylinder AB is to the total
force of the cylinder CD as the weight alone of
the cylinder AB is to the weight alone of the
cylinder CD, that is, as the volume of the cyl-
inder AB is to the volume CD: but these are as
the cubes of the diameters of their bases B and
D', and the resistances of the bases, being to each
other as their areas, are to each other conse-
quently as the squares of their diameters. There-
fore, the forces of the cylinders are to each other
in the sesquialteral ratio of the resistance of
their bases,
SIMP. This proposition strikes me as both
new and surprising: at first glance it is very dif-
ferent from anything which I myself should
have guessed: for since these figures are similar
THE TWO NEW SCIENCES
185
in all other respects, I should have certainly
thought that the forces and the resistances of
these cylinders would have borne to each other
the same ratio.
SAGR. This is the proof of the proposition to
which I referred, at the very beginning of our
discussion, as one imperfectly understood
by me.
SALV. For a while, Simplicio, I used to think,
as you do, that the resistances of similar solids
were similar; but a certain casual observation
showed me that similar solids do not exhibit a
strength which is proportiolnal to their size, the
larger ones being less fitted to undergo rough
usage, just as tall men are more apt than small
children to be injured by a fall. And, as we re-
marked at the outset, a large beam or column
falling from a given height will go to pieces
when under the same circumstances a small
scantling or small marble cylinder will not
break. It was this observation which led me to
the investigation of the fact which I am about
to demonstrate to you: it is a very remarkable
thing that, among the infinite variety of solids
which are similar one to another there are no
two of which the forces and the resistances of
these solids are related in the same ratio.
SIMP. You remind me now of a passage in
Aristotle's Questions in Mechanics in which he
tries to explain why it is that a wooden beam be-
comes weaker and can be more easily bent as it
grows longer, notwithstanding the fact that the
shorter beam is thinner and the longer one thick-
er: and, if I remember correctly, he explains it
in terms of the simple lever.
SALV. Very true: but, since this solution
seemed to leave room for doubt, Bishop di
Guevara, whose truly learned commentaries
have greatly enriched and illuminated this work,
indulges in additional clever speculations with
the hope of thus overcoming all difficulties; nev-
ertheless, even he is confused as regards this par-
ticular point, namely ,whether, when the length
and thickness of these solid figures increase in
the same ratio, their strength and resistance to
fracture, as well as to bending, remain constant.
After much thought upon this subject, I have
reached the following result. First I shall show
that,
PROPOSITION VII
Among heavy prisms and cylinders of similar fig-
ure, there is one and only one which under the stress
of its own weight lies just on the limit between
breaking and not breaking: so that every larger one
is unable to carry the load of its own weight and
breads; while every smaller one is able to withstand
some additional force tending to breal^ it.
Let AB be a heavy prism, the longest possible
that will just sustain its own weight, so that if it
be lengthened the least bit it will break. Then,
I say, this prism is unique among all similar
prisms— infinite in number— in occupying that
boundary line between breaking and not break-
ing; so that every larger one will break under its
own weight, and every smaller one will not break,
but will be able to withstand some force in addi-
tion to its own weight.
Let the prism CE be similar to, but larger
than, AB: then, I say, it will not remain intact
but will break under its own weight. Lay off the
portion CD, equal in length to AB. And, since,
the resistance of CD is to that of AB as the cube
of the thickness of CD is to the cube of the
thickness of AB, that is, as the prism CE is to
the similar prism AB, it follows that the weight
of CE is the utmost load which a prism of the
length CD can sustain; but the length of CE is
greater; therefore the prism CE will break. Now
Fig. 24
take another prism FG which is smaller than
AB. Let FH equal AB, then it can be shown in a
similar manner that the resistance [bending
strength] of FG is to that of AB as the prism FG
is to the prism AB provided the distance AB
that is FH, is equal to the distance FG; but AB
is greater than FG, and therefore the moment
of the prism FG applied at G is not sufficient to
break the prism FG.
SAGR. The demonstration is short and clear;
while the proposition which, at first glance, ap-
peared improbable is now seen to be both true
and inevitable. In order therefore to bring this
prism into that limiting condition which sepa-
rates breaking from not breaking, it would be
necessary to change the ratio between thickness
and length either by increasing the thickness or
by diminishing the length. An investigation of
this limiting state will, I believe, demand equal
ingenuity.
SALV. Nay, even more; for the question is
more difficult; this I know because I spent no
small amount of time in its discovery which I
now wish to share with you.
1 86
GALILEO GALILEI
PROPOSITION VIII
Given a cylinder or prism of the greatest length con-
sistent with its not breaking under its own weight',
and having given a greater length, to find the diam-
eter of another cylinder or prism of this greater length
which shall be the only and largest one capable of
withstanding its own weight.
Let EC be the largest cylinder capable of sus-
taining its own weight; and let DE be a length
greater than AC: the problem is to find the di-
ameter of the cylinder which, having the length
DE, shall be the largest one just able to with-
stand its own weight. Let / be a third propor-
tional to the lengths DE and AC\ let the diam-
eter FD be to the diameter BA as DE is to /;
draw the cylinder FE; then, among all cylinders
having the same proportions, this is the largest
and only one just capable of sustaining its own
weight.
Let M be a third proportional to DE and /:
also let 0 be a fourth proportional to DE, /, and
M ; lay off FG equal to AC. Now since the di-
ameter FD is to the diameter AB as the length
DE is to /, and since O is a fourth proportional
toDE,/and M, it followsthat FD3:E?3 = DE:O.
But the resistance [bending strength] of the cyl-
Fig. 25
inder DG is to the resistance of the cylinder EG
as the cube of FD is to the cube of BA: hence
the resistance of the cylinder DG is to that of
cylinder BCas the length DEis to 0. And since
the moment of the cylinder EC is held in equil-
ibrium by its resistance, we shall accomplish our
end (which is to prove that the moment of the
cylinder FE is equal to the resistance located at
FD), if we show that the moment of the cyl-
inder FE is to the moment of the cylinder #Cas
the resistance DF is to the resistance BA, that
is, as the cube of FD is to the cube of BA, or as
the length DE is to O. The moment of the cyl-
inder FE is to the moment of the cylinder
as the square of DE is to the square of AC, that
is, as the length DE is to /; but the moment of
the cylinder DG is to the moment of the cyl-
inder BC, as the square of DF is to the square of
BA, that is, as the square of DE is to the square
of /, or as the square of / is to the square of M,
or, as / is to O. Therefore by equating ratios, it
results that the moment of the cylinder FE is to
the moment of the cylinder BC as the length
DE is to 0, that is, as the cube of DF is to the
cube of BA, or as the resistance of the base DF
is to the resistance of the base BA1, which was to
be proven. *
SAGR. This demonstration, Salviati, is rather
long and difficult to keep in mind from a single
hearing. Will you not, therefore, be good
enough to repeat it?
SALV. As you like; but I would suggest in-
stead a more direct and a shorter proof: this
will, however, necessitate a different figure.
SAGR. The favor will be that much greater:
nevertheless, I hope you will oblige me by put-
ting into written form the argument just given
so that I may study it at my leisure.
SALV. I shall gladly do so. Let A denote a cyl-
inder of diameter DC and the largest capable of
sustaining its own weight: the problem is to
determine a larger cylinder which shall be at
once the maximum and the unique one capable
of sustaining its own weight.
Let E be such a cylinder, similar to A, having
the assigned length, and having a diameter KL.
Let MN be a third proportional to the two
D
Fig. 26
lengths DC and KL: let M N also be the diame-
ter of another cylinder, X, having the same
length as E: then, I say, X is the cylinder sought.
Now since the resistance of the base DC is to
the resistance of the base KL as the square of
DC is to the square of KL, that is, as the square
of KL is to the square ofMN, or, as the cylinder
E is to the cylinder X, that is, as the moment E
is to the moment X; and since also the resist-
THE TWO NEW SCIENCES
187
ance of the base KL is to the resistance of the
base MN as the cube of KL is to the cube of
MN, that is, as the cube of DC is to the cube of
KL, or, as the cylinder A is to the cylinder E,
that is, as the moment of A is to the moment
of E\ hence it follows, ex xquali in proportione
perturbata, that the moment of A is to the mo-
ment of X as the resistance of the base DC is
to the resistance of the base MN\ therefore
moment and resistance are related to each other
in prism X precisely as they are in prism A.
Let us now generalize the problem; then it
will read as follows:
Given a cylinder AC in which moment and resist-
ance are related in any manner whatsoever; let
DE be the length of another cylinder; then deter-
mine what its thickness must be in order that the
relation between its moment and resistance shall
be identical with that of the cylinder AC.
Using Fig. 25 in the same manner as above,
we may say that, since the moment of the cyl-
inder FE is to the moment of the portion DG
as the square of ED is to the square of FG, that
is, as the length DE is to /; and since the mo-
ment of the cylinder FG is to the moment of
the cylinder AC as the square of FD is to the
square of AB, or, as the square of ED is to the
square of/, or, as the square of / is to the square
of M, that is, as the length I is to O; it follows,
ex xquali, that the moment of the cylinder FE
is to the moment of the cylinder AC as the
length DE is to O, that is, as the cube of DE is
to the cube of /, or, as the cube of FD is to the
cube of AB, that is, as the resistance of the
base FD is to the resistance of the base AB\
which was to be proven.
From what has already been demonstrated,
you can plainly see the impossibility of increas-
ing the size of structures to vast dimensions
either in art or in nature; likewise the impossi-
bility of building ships, palaces, or temples of
enormous size in such a way that their oars,
yards, beams, iron-bolts, and, in short, all their
other parts will hold together; nor can nature
produce trees of extraordinary size because the
branches would break down under their own
weight; so also it would be impossible to build
up the bony structures of men, horses, or other
animals so as to hold together and perform
their normal functions if these animals were to
be increased enormously in height; for this in-
crease in height can be accomplished only by
employing a material which is harder and
stronger than usual, or by enlarging the size of
the bones, thus changing their shape until the
form and appearance of the animals suggest a
monstrosity. This is perhaps what our wise
Poet had in mind, when he says, in describing a
huge giant:
Impossible it is to reckon his height
So beyond measure is his size.1
To illustrate briefly, I have sketched a bone
whose natural length has been increased three
times and whose thickness has been multiplied
until, for a correspondingly large animal, it
would perform the same function which the
small bone performs for its small animal. From
the figures here shown you can see how out of
proportion the enlarged bone appears. Clearly
then if one wishes to maintain in a great giant
the same proportion of limb as that found in an
ordinary man he must either find a harder and
stronger material for making the bones, or he
must admit a diminution of strength in com-
parison with men of medium stature; for if his
height be increased inordinately he will fall
and be crushed under his own weight. Where-
as, if the size of a body be diminished, the
strength of that body is not diminished in the
same proportion; indeed the smaller the body
the greater its relative strength. Thus a small
dog could probably carry on his back two or
three dogs of his own size; but I believe that a
horse could not carry even one of his own size.
SIMP. This may be so; but I am led to doubt
it on account of the enormous size reached by
certain fish, such as the whale which, I under-
stand, is ten times as large as an elephant; yet
they all support themselves.
SALV. Your question, Simplicio, suggests an-
other principle, one which had hitherto escaped
my attention and which enables giants and other
animals of vast size to support themselves and
to move about as well as smaller animals do.
This result may be secured either by increasing
the strength of the bones and other parts in-
tended to carry not only their weight but also
the superincumbent load; or, keeping the pro-
1 ARIOSTO, Orlando Furtoso, xvii. 30.
1 88
GALILEO GALILEI
portions of the bony structure constant, the
skeleton will hold together in the same manner
or even more easily, provided one diminishes, in
the proper proportion, the weight of the bony
material, of the flesh, and of any thing else which
the skeleton has to carry. It is this second prin-
ciple which is employed by nature in the struc-
ture offish, making their bones and muscles not
merely light but entirely devoid of weight.
SIMP. The trend of your argument, Sal via ti,
is evident. Since fish live in water which on ac-
count of its density or, as others would say,
heaviness diminishes the weight of bodies im-
mersed in it, you mean to say that, for this rea-
son, the bodies of fish will be devoid of weight
and will be supported without injury to their
bones. But this is not all; for although the re-
mainder of the body of the fish may be without
weight, there can be no question but that their
bones have weight. Take the case of a whale's
rib, having the dimensions of a beam; who can
deny its great weight or its tendency to go to
the bottom when placed in water? One would,
therefore, hardly expect these great masses to
sustain themselves.
SALV. A very shrewd objection! And now, in
reply, tell me whether you have ever seen fish
stand motionless at will under water, neither
descending to the bottom nor rising to the top,
without the exertion of force by swimming ?
SIMP. This is a well-known phenomenon.
SALV. The fact then that fish are able to re-
main motionless under water is a conclusive rea-
son for thinking that the material of their bodies
has the same specific gravity as that of water;
accordingly, if in their make-up there are cer-
tain parts which are heavier than water there
must be others which are lighter, for otherwise
they would not produce equilibrium.
Hence, if the bones are heavier, it is necessary
that the muscles or other constituents of the
body should be lighter in order that their buoy-
ancy may counterbalance the weight of the
bones. In aquatic animals therefore, circum-
stances are just reversed from what they are
with land animals inasmuch as, in the latter, the
bones sustain not only their own weight but also
that of the flesh, while in the former it is the
flesh which supports not only its own weight
but also that of the bones. We must therefore
cease to wonder why these enormously large
animals inhabit the water rather than the land,
that is to say, the air.
SIMP. I am convinced and I only wish to add
that what we call land animals ought really
to be called air animals, seeing that they live in
the air, are surrounded by air, and breathe air,
SAGR. I have enjoyed Simplicio's discussion
including both the question raised and its an-
swer. Moreover, I can easily understand that
one of these giant fish, if pulled ashore, would
not perhaps sustain itself for any great length of
time, but would be crushed under its own mass
as soon as the connections between the bones
gave way.
SALV. I am inclined to your opinion; and, in-
deed, I almost think that the same thing would
happen in the case of a very big ship which floats
on the sea without going to pieces under its load
of merchandise and armament, but which on
dry land and in air would probably fall apart.
But let us proceed and show how:
Given a prism or cylinder, also its own weight and
the maximum load which it can carry, it is then
possible to find a maximum length beyond which
the cylinder cannot be prolonged without breaking
under its own weight.
Let AC indicate both the prism and its own
weight; also let D represent the maximum load
which the prism can carry at the end C without
fracture; it is required to find the maximum to
which the length of the said prism can be in-
creased without breaking. Draw AH of such a
length that the weight of the prism AC is to the
sum of AC and twice the weight D as the length
CA is to AH\ and let AG be a mean proportion-
al between CA and AH\ then, I say, AG is the
length sought. Since the moment of the weight
D attached at the point C is equal to the mo-
ment of a weight twice as large as D placed at
the middle point AC, through which the weight
Ai
IG
-H
Fig. 28
of the prism ^Cacts, it follows that the moment
of the resistance of the prism /4C located at A is
equivalent to twice the weight D plus the weight
of AC, both acting through the middle point of
AC. And since we have agreed that the moment
of the weights thus located, namely, twice D
plus AC, bears to the moment of AC the same
ratio which the length HA bears to CA and
since AGisa mean proportional between these
two lengths, it follows that the moment of twice
Dplus AC is to the moment of A C as the square
THE TWO NEW SCIENCES
189
of GA is to the square of CA. But the moment
arising from the weight of the prism GA is to
the moment of A C as the square of GA is to the
square of CA ; thence AG is the maximum length
sought, that is, the length up to which the prism
AC may be prolonged and still support itself,
but beyond which it will break.
Hitherto we have considered the moments
and resistances of prisms and solid cylinders
fixed at one end with a weight applied at the
other end; three cases were discussed, namely,
that in which the applied force was the only
one acting, that in which the weight of the
prism itself is also taken into consideration, and
that in which the weight of the prism alone is
taken into consideration. Let us now consider
these same prisms and cylinders when sup-
ported at both ends or at a single point placed
somewhere between the ends. In the first place,
I remark that a cylinder carrying only its own
weight and having the maximum length, be-
yond which it will break, will, when supported
either in the middle or at both ends, have
twice the length of one which is mortised into
a wall and supported only at one end. This is
very evident because, if we denote the cylinder
by ABC and if we assume that one-half of it,
ABj is the greatest possible length capable of
supporting its own weight with one end fixed
at B, then, for the same reason, if the cylinder
is carried on the point G, the first half will be
counterbalanced by the other half EC. So also
in the case of the cylinder DEF, if its length be
Fig. 29
such that it will support only one-half this
length when the end D is held fixed, or the
other half when the end F is fixed, then it is
evident that when supports, such as H and /,
are placed under the ends D and F respectively
the moment of any additional force or weight
placed at E will produce fracture at this point.
A more intricate and difficult problem is the
following: neglect the weight of a solid such as
the preceding and find whether the same force
or weight which produces fracture when ap-
plied at the middle of a cylinder, supported at
both ends, will also break the cylinder when ap-
plied at some other point nearer one end than
the other.
Thus, for example, if one wished to break a
stick by holding it with one hand at each end
and applying his knee at the middle, would the
same force be required to break it in the same
manner if the knee were applied, not at the
middle, but at some point nearer to one end ?
SAGR. This problem, I believe, has been
touched upon by Aristotle in his Questions in
Mechanics.
SALV. His inquiry however is not quite the
same; for he seeks merely to discover why it is
that a stick may be more easily broken by tak-
ing hold, one hand at each end of the stick, that
is, far removed from the knee, than if the hands
were closer together. He gives a general ex-
planation, referring it to the lengthened lever
arms which are secured by placing the hands at
the ends of the stick. Our inquiry calls for
something more: what we want to know is
whether, when the hands are retained at the
ends of the stick, the same force is required to
break it wherever the knee be placed.
SAGR. At first glance this would appear to be
so, because the two lever arms exert, in a cer-
tain way, the same moment, seeing that as one
grows shorter the other grows correspondingly
longer.
SALV. Now you see how readily one falls into
error and what caution and circum-
spection are required to avoid it.
What you have just said appears at
first glance highly probable, but on
closer examination it proves to be
quite far from true; as will be seen
from the fact that whether the knee
— the fulcrum of the two levers —
be placed in the middle or not
makes such a difference that, if frac-
ture is to be produced at any other
point than the middle, the break-
ing force at the middle, even when
multiplied four, ten, a hundred, or a thousand
times would not suffice. To begin with we shall
offer some general considerations and then pass
to the determination of the ratio in which the
breaking force must change in order to produce
fracture at one point rather than another.
Let AB denote a wooden cylinder which is to
be broken in the middle, over the supporting
point C, and let DE represent an identical cyl-
inder which is to be broken just over the sup-
190
GALILEO GALILEI
porting point F which is not in the middle.
First of all it is clear that, since the distances
AC and CB are equal, the forces applied at the
extremities B and A must also be equal. Sec-
ondly since the distance DP is less than the dis-
tance AC the moment of any force acting at D
is less than the moment of the same force at A>
that is, applied at the distance CA\ and the mo-
ments are less in the ratio of the length DP to
AC\ consequently it is necessary to increase the
force at D in order to overcome, or even to
balance, the resistance at F', but in comparison
with the length AC the distance DP can be
diminished indefinitely: in order therefore to
counterbalance the resistance at P it will be
necessary to increase indefinitely the force ap-
plied at D. On the other hand, in proportion
as we increase the distance FE over that of CB,
we must diminish the force at E in order to
counterbalance the resistance at T7; but the dis-
tance FE, measured in terms of CB, cannot be
increased indefinitely by sliding the fulcrum F
toward the end Z); indeed, it cannot even be
made double the length CB. Therefore the
force required at E to balance the resistance at
F will always be more than half that required
at B. It is clear then that, as the fulcrum F ap-
proaches the end D, we must of necessity in-
definitely increase the sum of the forces applied
at E and D in order to balance, or overcome,
the resistance at F.
SAGR. What shall we say, Simplicio? Must
we not confess that geometry is the most pow-
erful of all instruments for sharpening the wit
and training the mind to think correctly ? Was
not Plato perfectly right when he wished that
his pupils should be first of all well grounded in
mathematics ? As for myself, I quite understood
the property of the lever and how, by increas-
ing or diminishing its length, one can increase
or diminish the moment of force and of resist-
ance; and yet, in the solution of the present
problem I was not slightly, but greatly, de-
ceived.
SIMP. Indeed I begin to understand that
while logic is an excellent guide in discourse, it
does not, as regards stimulation to discovery,
compare with the power of sharp distinction
which belongs to geometry.
SAGR. Logic, it appears to me, teaches us how
to test the conclusiveness of any argument or
demonstration already discovered and com-
pleted; but I do not believe that it teaches
us to discover correct arguments and demon-
strations. But it would be better if Salviati
were to show us in just what proportion the
forces must be increased in order to produce
fracture as the fulcrum is moved from one
point to another along one and the same wood-
en rod.
SALV. The ratio which you desire is deter-
mined as follows:
If upon a cylinder one mar^s two points at which
fracture is to be produced, then the resistances at
these two points will bear to each other the in-
verse ratio of the rectangles formed by the dis-
tances from the respective points to the ends of the
cylinder.
Let A and B denote the least forces which
will bring about fracture of the cylinder at C;
likewise E and F the smallest forces which will
break it at D. Then, I say, that the sum of the
forces A and B is to the sum of the forces E and
F as the area of the rectangle AD.DB is to the
area of the rectangle AC.CB. Because the sum
of the forces A and B bears to the sum of the
forces E and F a ratio which is the product of
the three following ratios, namely, (A-\-B)/By
B/F, and F/(F+E) ; but the length BA is to the
length CA as the sum of the forces A and B is
Fig. 31
to the force E\ and, as the length DB is to the
length CB, so is the force B to the force F\ also
as the length AD is to AB, so is the force F to
the sum of the forces F and E.
Hence it follows that the sum of the forces A
and B bears to the sum of the forces E and F a
ratio which is the product of the three follow-
ing ratios, namely, BA/CA, ED I EC, and AD I
AB. But DA/CA is the product of DA/BA and
BA/CA. Therefore the sum of the forces A and
B bears to the sum of the forces E and F a ratio
which is the product of DA:CA and DB:CB.
THE TWO NEW SCIENCES
But the rectangle AD.DB bears to the rec-
tangle AC. CB a ratio which is the product of
DA/CA and DB/CB. Accordingly, the sum of
the forces A and B is to the sum of the forces E
and F as the rectangle AD. DB is to the rec-
tangle AC. CB, that is, the resistance to frac-
ture at C is to the resistance to fracture at D as
the rectangle AD.DB is to the rectangle
AC. CB. Q. E. D.
Another rather interesting problem may be
solved as a consequence of this theorem,
namely,
Given the maximum weight which a cylinder or
prism can support at its middle-point where the
resistance is a minimum, and given also a larger
weight, find that point in the cylinder for which this
larger weight is the maximum load that can be
supported.
Let that one of the given weights which is
larger than the maximum weight supported at
the middle of the cvlinder AB bear to this max-
imum weight the same ratio which the length
E bears to the length F. The problem is to find
that point in the cylinder at which this larger
weight becomes the maximum that can be sup-
ported. Let G be a mean proportional between
the lengths E and F. Draw AD and S so that
they bear to each other the same ratio as E to
G; accordingly S will be less than AD.
Let AD be the diameter of a semicircle AHD,
in which take AH equal to 5; join the points H
and D and lay off DR equal to HD. Then, L
say, R is the point sought, namely, the point at
which the given weight, greater than the max-
imum supported at the middle of the cylinder
D, would become the maximum load.
On AB as diameter draw the semicircle
ANB: erect the perpendicular /Wand join the
points N and D. Now since the sum of the
squares on NR and RD is equal to the square of
ND, that is, to the square of AD, or to the sum
of the squares of AH and HD] and, since the
square of HD is equal to the square of DR, it
follows that the square of NR, that is, the rec-
tangle AR.RB, is equal to the square of AH,
also therefore to the square of 5; but the square
of S is to the square of AD as the length F is to
the length E, that is, as the maximum weight
supported at D is to the larger of the two given
weights. Hence the latter will be the maximum
load which can be carried at the point R-, which
is the solution sought.
SAGR. Now I understand thoroughly; and I
am thinking that, since the prism AB grows
constantly stronger and more resistant to the
pressure of its load at points which are more
and more removed from the middle, we could
in the case of large heavy beams cut away a
considerable portion near the ends which would
notably lessen the weight, and which, in the
beam work of large rooms, would prove to be
of great utility and convenience.
It would be a fine thing if one could discover
the proper shape to give a solid in order to
make it equally resistant at every point, in
which case a load placed at the middle would
not produce fracture more easily than if placed
at any other point.
SALV. I was just on the point of mentioning
an interesting and remarkable fact connected
with this very question. My meaning will be
clearer if I draw a figure. Let DB represent a
prism; then, as we have already shown, its re-
sistance to fracture at the end AD, owing to a
load placed at the end B, will be less than the
resistance at CI in the ratio of the length CB to
AB. Now imagine this same prism to be cut
through diagonally along the line FB so that
the opposite faces will be triangular; the side
facing us will be FAB. Such a solid will have
properties different from those of the prism;
for, if the load remain at B, the resistance
against fracture [bending strength] at C will be
less than that at A in the ratio of the length CB
to the length AB. This is easily proved: for if
CNO represents a cross-section parallel to AFD,
then the length FA bears to the length CN, in
D L
the triangle FAB, the same ratio which the
length AB bears to the length CB. Therefore,
if we imagine A and C to be the points at which
the fulcrum is placed, the lever arms in the two
192
GALILEO GALILEI
cases BA, AF and BC, CN will be proportional.
Hence the moment of any force applied at B
and acting through the arm BA, against a re-
sistance placed at a distance AF wUl be equal
to that of the same force at B acting through
the arm BC against the same resistance located
at a distance CN. But now, if the force still be
applied at B, the resistance to be overcome
when the fulcrum is at G, acting through the
arm CN, is less than the resistance with the ful-
crum at A in the same proportion as the rec-
tangular cross-section CO is less than the rec-
tangular cross-section AD, that is, as the length
CN if less than AF, or CB than BA.
Consequently the resistance to fracture at
C, offered by the portion OBC, is less than the
resistance to fracture at A, offered by the en-
tire block DAB, in the same proportion as
the length CB is smaller than the length AB.
By this diagonal saw-cut we have now re-
moved from the beam, or prism DB, a portion,
i.e., a half, and have left the wedge, or triangu-
lar prism, FBA. We thus have two solids pos-
sessing opposite properties; one body grows
stronger as it is shortened while the other grows
weaker. This being so it would seem not merely
reasonable, but inevitable, that there exists a
line of section such that, when the superfluous
material has been removed, there will remain
a solid of such figure that it will offer the same
resistance at all points.
SIMP. Evidently one must, in passing from
greater to less, encounter equality.
SAGR. But now the question is what path the
saw should follow in making the cut.
SIMP. It seems to me that this ought not to
be a difficult task: for if by sawing the prism
along the diagonal line and removing half of the
material, the remainder acquires a property
just the opposite to that of the entire prism, so
that at every point where the latter gains
strength the former becomes weaker, then it
seems to me that by taking a middle path, i.e.,
by removing half the former half, or one-quar-
ter of the whole, the strength of the remaining
figure will be constant at all those points where,
in the two previous figures, the gain in one was
equal to the loss in the other.
SALV. You have missed the mark, Simplicio.
For, as I shall presently show you, the amount
which you can remove from the prism without
weakening it is not a quarter but a third. It now
remains, as suggested by Sagredo, to discover the
path along which the saw must travel: this, as I
shall prove, must be a parabola. But it is first
necessary to demonstrate the following lemma:
If the fulcrums are so placed under two levers or
balances that the arms through which the forces
act are to each other in the same ratio as the squares
of the arms through which the resistances act, and
if these resistances are to each other in the same
ratio as the arms, through which they act, then the
forces will be equal.
Let AB and CD represent two levers whose
lengths are divided by their fulcrums in such a
£
B
Fig. 34
way as to make the distance EB bear to the
distance FD a ratio which is equal to the square
of the ratio between the distances EA and FC.
Let the resistances located at A and C be to
each other as EA is to FC. Then, I say, the
forces which must be applied at B and D in
order to hold in equilibrium the resistances at
A and C are equal. Let EG be a mean propor-
tional between EB and FD. Then we shall have
BE:EG = EG:FD = AE:CF. But this last ratio
is precisely that which we have assumed to
exist between the resistances at A and C. And
since EG:FD = AE:CF, it follows, permutando,
that EG:AE=FD:CF. Seeing that the dis-
tances DC and GA are divided in the same
ratio by the points JF and E, it follows that the
same force which, when applied at D, will
equilibrate the resistance at C, would if applied
at G equilibrate at A a resistance equal to that
found at C.
But one datum of the problem is that the
resistance at A is to the resistance at C as the
distance AE is to the distance CF, or as BE is to
EG. Therefore the force applied at G, or rather
at D, will, when applied at B, just balance the
resistance located at A. Q. E. D.
This being clear draw the parabola FNB in
the face FB of the prism DB. Let the prism be
sawed along this parabola whose vertex is at B.
The portion of the solid which remains will be
included between the base AD, the rectangular
plane AG, the straight line BG and the surface
DGBF, whose curvature is identical with that
of the parabola FNB. This solid will have, I say,
the same strength at every point. Let the solid
be cut by a plane CO parallel to the plane AD.
Imagine the points A and C to be the fulcrums
of two levers of which one will have the arms
BA and AF; the other BC and CN. Then since
in the parabola FBA, we have BAiBC^UF2:
CN2, it is clear that the arm BA of one lever is
THE TWO NEW SCIENCES
'93
35
to the arm BC of the other lever as the square
of the arm AF is to the square of the other arm
CN. Since the resistance to be balanced by the
lever BA is to the resistance to be balanced by
the lever BC in the same ratio as the rectangle
DA is to the rectangle OC, that is as the length
AF is to the length CN, which two lengths are
the other arms of the levers, it follows, by the
lemma just demonstrated, that the same force
which, when applied at BG will equilibrate the
resistance at DA, will also balance the resist-
ance at CO. The same is true for any other sec-
tion. Therefore this parabolic solid is equally
strong throughout.
It can now be shown that, if the prism be
sawed along the line of the parabola FNB, one-
third part of it will be removed; because the
rectangle FB and the surface FNBA bounded
by the parabola are the bases of two solids in-
cluded between two parallel planes, i.e., be-
tween the rectangles FB and DG\ consequently
the volumes of these two solids bear to each
other the same ratio as their bases. But the area
of the rectangle is one and a half times as large
as the area FNBA under the parabola; hence by
cutting the prism along the parabola we remove
one-third of the volume. It is thus seen how one
can diminish the weight of a beam by as much
as thirty-three per cent without diminishing its
strength; a fact of no small utility in the con-
struction of large vessels, and especially in sup-
porting the decks, since in such structures
lightness is of prime importance.
SAGR. The advantages derived from this fact
are so numerous that it would be both weari-
some and impossible to mention them all; but
leaving this matter to one side, I should like to
learn just how it happens that diminution of
weight is possible in the ratio above stated. I
can readily understand that, when a section is
made along the diagonal, one-half the weight is
removed; but, as for the parabolic section re-
moving one-third of the prism, this I can only
accept on the word of Salviati who is always
reliable; however, I prefer first-hand knowledge
to the word of another.
SALV. You would like then a demonstration
of the fact that the excess of the volume of a
prism over the volume of what we have called
the parabolic solid is one-third of the entire
prism. This I have already given you on a pre-
vious occasion; however I shall now try to re-
call the demonstration in which I remember
having used a certain lemma from Archimedes'
book On Spirals,1 namely, Given any number
of lines, differing in length one from another by
a common difference which is equal to the
shortest of these lines; and given also an equal
number of lines each of which has the same
length as the longest of the first-mentioned
series; then the sum of the squares of the lines
of this second group will be less thaf! three
times the sum of the squares of the lines in the
first group. But the sum of the squares of the
second group will be greater than three times
the sum of the squares of all excepting the
longest of the first group.
Assuming this, inscribe in the rectangle ACBP
the parabola AB. We have now to prove that
the mixed triangle BAP whose sides are BPand
PA, and whose base is the parabola BA, is a
third part of the entire rectangle CP. If this is
not true it will be either greater or less than a
third. Suppose it to be less by an area which is
represented by X. By drawing lines parallel to
the sides BP and CA, we can divide the rec-
tangle CPinto equal parts; and if the process be
continued we shall finally reach a division into
parts so small that each of them will be smaller
^— ^_
T
r
O
N
M
L
K
A
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S
H
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n
F
X
Q
£
s
G
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Fig. 36
than the area X\ let the rectangle OB represent
one of these parts and, through the points
where the other parallels cut the parabola, draw
lines parallel to AP. Let us now describe about
our "mixed triangle" a figure made up of rec-
tangles such as BO, IN, HM, FL, EK, and GA\
this figure will also be less than a third part of
the rectangle CP because the excess of this fig-
ure above the area of the "mixed triangle" is
much smaller than the rectangle BO which we
have already made smaller than X.
1 See Archimedes, On Spirals, p. 482*
194
GALILEO GALILEI
SAGR. More slowly, please; for I do not see
how the excess of this figure described about
the "mixed triangle" is much smaller than the
rectangle BO.
SALV. Does not the rectangle BO have an
area which is equal to the sum of the areas of
all the little rectangles through which the parab-
ola passes ? I mean the rectangles BI, IHt HF,
FE, EG, and GA of which only a part lies out-
side the "mixed triangle." Have we not taken
the rectangle BO smaller than the area X?
Therefore if, as our opponent might say, the
triangle plus X is equal to a third part of this
rectangle CP, the circumscribed figure, which
adds to the triangle an area less than X, will
still remain smaller than a third part of the
rectangle, CP. But this cannot be, because this
circumscribed figure is larger than a third of
the area. Hence it is not true that our "mixed
triangle" is less rhan a third of the rectangle.
SAGR. You have cleared up my difficulty;
but it still remains to be shown that the cir-
cumscribed figure is larger than a third part of
the rectangle CP, a task which will not, I be-
lieve, prove so easy.
SALV. There is nothing very difficult about
it. Since in the parabola D£*:ZG2 = D/4:/4Z =
rectangle KE\ rectangle AG, seeing that the
altitudes of these two rectangles, AK and \ KL,
are equal, it follows that ED2:ZG2 = LA*iAK*=z
rectangle KE: rectangle KZ. In precisely the
same manner it may be shown that the other
rectangles LF, MH, NI, OB, stand to one an-
other in the same ratio as the squares of the
lines MA, NA, OA, PA.
Let us now consider the circumscribed fig-
ure, composed of areas which bear to each other
the same ratio as the squares of a series of lines
whose common difference in length is equal to
the shortest one in the series; note also that the
rectangle CP is made up of an equal number of
areas each equal to the largest and each equal
to the rectangle OB. Consequently, according
to the lemma of Archimedes, the circumscribed
figure is larger than a third part of the rec-
tangle CP; but it was also smaller, which is im-
possible. Hence the "mixed triangle" is not less
than a third part of the rectangle CP.
Likewise, I say, it cannot be greater. For, let
us suppose that it is greater than a third part of
the rectangle CP and let the area X represent
the excess of the triangle over the third part of
the rectangle CP; subdivide the rectangle into
equal rectangles and continue the process until
one of these subdivisions is smaller than the
area X. Let BO represent such a rectangle
smaller than X. Using the above figure, we have
in the "mixed triangle" an inscribed figure,
made up of the rectangles VO, TN, SM, RL,
and QK, which will not be less than a third
part of the large rectangle CP.
For the "mixed triangle" exceeds the in-
scribed figure by a quantity less than that by
which it exceeds the third part of the rectangle
CP; to see that this is true we have only to re-
member that the excess of the triangle over the
third part of the rectangle CP is equal to the
area X, which is less than the rectangle BO,
which in turn is much less than the excess of the
triangle over the inscribed figure. For the rec-
tangle BO is made up of the small rectangles
AG, GE, EF, FH, HI, and /£; and the excess of
the triangle over the inscribed figure is less than
half the sum of these little rectangles. Thus
since the triangle exceeds the third part of the
rectangle CP by an amount X, which is more
than that by which it exceeds the inscribed fig-
ure, the latter will also exceed the third part of
the rectangle, CP. But, by the lemma which we
have assumed, it is smaller. For the rectangle
CP, being the sum of the largest rectangles,
bears to the component rectangles of the in-
scribed figure the same ratio which the sum of
all the squares of the lines equal to the longest
bears to the squares of the lines which have a
common difference, after the square of the
longest has been subtracted.
Therefore, as in the case of squares, the sum
total of the largest rectangles, i.e., the rectangle
CP, is greater'than three times the sum total of
those having a common difference minus the
largest; but these last make up the inscribed
figure. Hence the "mixed triangle" is neither
greater nor less than the third part of rectangle
CP; it is therefore equal to it.
SAGR. A fine, clever demonstration; and all
the more so because it gives us the quadrature
of the parabola, proving it to be four-thirds of
the inscribed triangle, a fact which Archimedes
demonstrates by means of two different, but
admirable, series of many propositions. This
same theorem has also been recently estab-
lished by Luca Valerio, the Archimedes of our
age; his demonstration is to be found in his
book dealing with the centres of gravity of
solids.
SALV. A book which, indeed, is not to be
placed second to any produced by the most
eminent geometers either of the present or of
the past; a book which, as soon as it fell into the
hands of our Academician, led him to abandon
his own researches along these lines; for he saw
THE TWO NEW SCIENCES
how happily everything had been treated and
demonstrated by Valerio.
SAGR. When I was informed of this event by
the Academician himself, I begged of him to
show the demonstrations which he had discov-
ered before seeing Valerie's book; but in this I
did not succeed.
SALV. I have a copy of them and will show
them to you; for you will enjoy the diversity of
method employed by these two authors in
reaching and proving the same conclusions; you
will also find that some of these conclusions are
explained in different ways, although both are
in fact equally correct.
SAGR. I shall be much pleased to see them
and will consider it a great favor if you will
bring them to our regular meeting. But in the
meantime, considering the strength of a solid
formed from a prism by means of a parabolic
section, would it not, in view of the fact that
this result promises to be both interesting and
useful in many mechanical operations, be a fine
thing if you were to give some quick and easy
rule by which a mechanician might draw a parab-
ola upon a plane surface ?
SALV. There are many ways of tracing these
curves; 1 will mention merely the two which
are the quickest of all. One of these is really re-
markable; because by it I can trace thirty or
forty parabolic curves with no less neatness and
precision, and in a shorter time than another
man can, by the aid of a compass, neatly draw
four or six circles of different sizes upon paper.
1 take a perfectly round brass ball about the
size of a walnut and project it along the surface
of a metallic mirror held in a nearly upright
position, so that the ball in its motion will press
slightly upon the mirror and trace out a fine
sharp parabolic line; this parabola will grow
longer and narrower as the angle of elevation
increases. The above experiment furnishes clear
and tangible evidence that the path of a pro-
jectile is a parabola; a fact first observed by our
friend and demonstrated by him in his book on
motion which we shall take up at our next
meeting. In the execution of this method, it is
advisable to slightly heat and moisten the ball
by rolling in the hand in order that its trace
upon the mirror may be more distinct.
The other method of drawing the desired
curve upon the face of the prism is the follow-
ing: Drive two nails into a wall at a convenient
height and at the same level; make the distance
between these nails twice the width of the rec-
tangle upon which it is desired to trace the
semiparabola. Over these two nails hang a light
chain of such a length that the depth of its sag
is equal to the length of the prism. This chain
will assume the form of a parabola,1 so that if
this form be marked by points on the wall we
shall have described a complete parabola which
can be divided into two equal parts by drawing
a vertical line through a point midway between
the two nails. The transfer of this curve to the
two opposing faces of the prism is a matter of
no difficulty; any ordinary mechanic will know
how to do it.
By use of the geometrical lines drawn upon
our friend's compass, one may easily lay off
those points which will locate this same curve
upon the same face of the prism.
Hitherto we have demonstrated numerous
conclusions pertaining to the resistance which
solids offer to fracture. As a starting point for
this science, we assumed that the resistance
offered by the solid to a straight-away pull was
known; from this base one might proceed to the
discovery of many other results and their dem-
onstrations; of these results the number to be
found in nature is infinite. But, in order to
bring our daily conference to an end, I wish to
discuss the strength of hollow solids, which are
employed in art— and still oftener in nature —
in a thousand operations for the purpose of
greatly increasing strength without adding to
weight; examples of these are seen in the bones
of birds and in many kinds of reeds which are
light and highly resistant both to bending and
breaking. For if a stem of straw which carries
a head of wheat heavier than the entire stalk
were made up of the same amount of material
in solid form it would offer less resistance to
bending and breaking. This is an experience
which has been verified and confirmed in prac-
tice, where it is found that a hollow lance or a
tube of wood or metal is much stronger than
would be a solid one of the same length and
weight, one which would necessarily be thinner;
men have discovered, therefore, that in order
to make lances strong as well as light they must
make them hollow. We shall now show that:
In the case of two cylinders, one hollow the other
solid but having equal volumes and equal lengths,
their resistances are to each other in the ratio of
their diameters.
Let AE denote a hollow cylinder and IN a solid
one of the same weight and length; then, I say,
that the resistance against fracture exhibited by
the tube AE bears to that of the solid cylinder
IN the same ratio as the diameter AB to the
1 It is now known that this curve is not a parabola but
a catenary. TRANS.
196
GALILEO GALILEI
diameter /£,. This is very evident; for since the
tube and the solid cylinder IN have the same
WlWlhUtlliiillU
N
Fig- 37
volume and length, the area of the circular base
IL will be equal to that of the annulus AB
which is the base of the tube AE. (By annulus
is here meant the area which lies between two
concentric circles of different radii.) Hence their
resistances to a straight-away pull are equal;
but in producing fracture by a transverse pull
we employ, in the case of the cylinder IN, the
length LN as one lever arm, the point L as a
fulcrum, and the diameter LI, or its half, as the
opposing lever arm: while in the case of the
tube, the length BE which plays the part of the
first lever arm is equal to LN, the opposing
lever arm beyond the fulcrum, B, is the diam-
eter AB, or its half. Manifestly then the re-
sistance of the tube exceeds that of the solid
cylinder in the proportion in which the diam-
eter AB exceeds the diameter IL which is the
desired result. Thus the strength of a hollow
tube exceeds that of a solid cylinder in the ra-
tio of their diameters whenever the two are
made of the same material and have the same
weight and length.
It may be well next to investigate the general
case of tubes and solid cylinders of constant
length, but with the weight and the hollow por-
tion variable. First we shall show that:
Given a hollow tube, a solid cylinder may be de-
termined which will be equal to it.
The method is very simple. Let AB denote
the external and CD the internal diameter of
the tube. In the larger circle lay off the line AE
equal in length to the diameter CD\ join the
points E and B. Now since the angle at E in-
scribed in a semicircle, AEB, is a right-angle,
the area of the circle whose diameter is AB is
equal to the sum of the areas of the two circles
whose respective diameters are AE and EB.
But AE is the diameter of the hollow portion
of the tube. Therefore the area of the circle
whose diameter is EB is the same as the area of
the annulus ACBD. Hence a solid cylinder of
circular base having a diameter EB will have
the same volume as the walls of the tube of
equal length.
By use of this theorem, it is easy: To find the
ratio between the resistance of any tube and that of
any cylinder of equal length. Let ABE denote a
tube and RSM a cylinder of equal length: it
is required to find the ratio between their re-
sistances. Using the preceding proposition, de-
termine a cylinder ILN which shall have the
R
Fig. 38
Fig- 39
same volume and length as the tube. Draw a
line F of such a length that it will be related to
IL and RS (diameters of the bases of the cylin-
ders IN and RM), as follows: V:RS = RS:IL.
Then, I say, the resistance of the tube AE is to
that of the cylinder RM as the length of the line
AB is to the length V. For, since the tube AE
is equal both in volume and length, to the
cylinder IN, the resistance of the tube will bear
to the resistance of the cylinder the same ratio
as the line AB to IL; but the resistance of the
cylinder IN is to that of the cylinder RM as the
cube of IL is to the cube of RS, that is, as the
length IL is to length V: therefore, ex aequali,
the resistance of the tube AE bears to the re-
sistance of the cylinder RM the same ratio as
the length AB to V. Q. E. D.
THIRD DAY
CHANGE OF POSITION
MY purpose is to set forth a very new science
dealing with a very ancient subject. There is,
in nature, perhaps nothing older than motion,
concerning which the books written by philoso-
phers are neither few nor small; nevertheless, I
have discovered by experiment some properties
of it which are worth knowing and which have
not hitherto been either observed or demon-
strated. Some superficial observations have been
made, as, for instance, that the free motion of a
heavy falling body is continuously accelerated;
but to just what extent this acceleration occurs
has not yet been announced; for so far as I
know, no one has yet pointed out that the dis-
tances traversed, during equal intervals of time,
by a body falling from rest, stand to one another
in the same ratio as the odd numbers beginning
with unity.
It has been observed that missiles and pro-
jectiles describe a curved path of some sort;
however, no one has pointed out the fact that
this path is a parabola. But this and other facts,
not few in number or less worth knowing, I
have succeeded in proving; and what I consider
more important, there have been opened up to
this vast and most excellent science, of which my
work is merely the beginning, ways and means
by which other minds more acute than mine will
explore its remote corners.
This discussion is divided into three parts; the
first part deals with motion which is steady or
uniform; the second treats of motion as we find
it accelerated in nature; the third deals with the
so-called violent motions and with projectiles.
UNIFORM MOTION
In dealing with steady or uniform motion,
we need a single definition which I give as
follows: _.
DEFINITION
By steady or uniform motion, I mean one in
which the distances traversed by the moving
particle during any equal intervals of time, are
themselves equal.
CAUTION
We must add to the old definition (which de-
fined steady motion simply as one in which
equal distances are traversed in equal times) the
word "any," meaning by this, all equal inter-
vals of time; for it may happen that the moving
body will traverse equal distances during some
equal intervals of time and yet the distances tra-
versed during some small portion of these time-
intervals may not be equal, even though the
time-intervals be equal.
From the above definition, four axioms fol-
low, namely: A T
7 AXIOM I
In the case of one and the same uniform mo-
tion, the distance traversed during a longer in-
terval of time is greater than the distance tra-
versed during a shorter interval of time.
AXIOM II
In the case of one and the same uniform mo-
tion, the time required to traverse a greater
distance is longer than the time required for a
less distance. A TTT
AXIOM III
In one and the same interval of time, the dis-
tance traversed at a greater speed is larger than
the distance traversed at a less speed.
AXIOM IV
The speed required to traverse a longer dis-
tance is greater than that required to traverse
a shorter distance during the same time-interval.
THEOREM I, PROPOSITION I
If a moving panicky carried uniformly at a con-
stant speed, traverses two distances the time-inter-
vals required are to each other in the ratio of these
distances.
Let a particle move uniformly with constant
speed through two distances AB, BC, and let
the time required to traverse AB be represented
by DE\ the time required to traverse BC, by
EF\ then I say that the distance AB is to the
distance BC as the time DE is to the time EF.
Let the distances and times be extended on
197
I, I
GALILEO GALILEI
, . . , , , ID fE IF .
I i IK
G.
i I i i i i i [ [ i
i i i i TA IB Ic
i i i I j I 1
Fig. 40
both sides towards G, H and /, K; let AG be di-
vided into any number whatever of spaces each
equal to AB, and in like manner lay off in Dl
exactly the same number of time-intervals each
equal to DE. Again lay off in CH any number
whatever of distances each equal to BC\ and in
FK exactly the same number of time-intervals
each equal to EF; then will the distance BG and
the time El be equal and arbitrary multiples of
the distance BA and the time ED; and likewise
the distance HB and the time KE are equal and
arbitrary multiples of the distance CB and the
time FE.
And since DE is the time required to traverse
AB, the whole time El will be required for the
whole distance BG, and when the motion is uni-
form there will be in El as many time-intervals
each equal to DE as there are distances in BG
each equal to BA; and likewise it follows that
KE represents the time required to traverse HB.
Since, however, the motion is uniform, it fol-
lows that if the distance GB is equal to the dis-
tance BH, then must also the time IE be equal
to the time EK; and if GB is greater than BH,
then also IE will be greater than EK; and if less,
less.1 There are then four quantities, the first
AB, the second BC, the third DE, and the
fourth EF; the time IE and the distance GB
are arbitrary multiples of the first and the third,
namely of the distance AB and the time DE.
But it has been proved that both of these lat-
ter quantities are either equal to, greater than,
or less than the time EK and the space BH,
which are arbitrary multiples of the second and
the fourth. Therefore the first is to the second,
namely the distance AB is to the distance BC,
as the third is to the fourth, namely the time
DE is to the time EF. Q. E. D.
THEOREM II, PROPOSITION II
If a moving particle traverses two distances in equal
intervals of time, these distances will bear to each
other the same ratio as the speeds. And conversely
if the distances are as the speeds then the times are
equal.
Referring to Fig. 40, let AB and BC represent
the two distances traversed in equal time-inter-
vals, the distance AB for instance with the
velocity DE, and the distance BC with the ve-
!Scc Euclid, V. 5.
locity EF. Then, I say, the distance AB is to the
distance #Cas the velocity DEis to the velocity
EF. For if equal multiples of both distances and
speeds be taken, as above, namely, GB and
IE of AB and DE respectively, and in like man-
ner HB and KEofBCand EF, then one may in-
fer, in the same manner as above, that the
multiples GB and IE are either less than, equal
to, or greater than equal multiples of BH and
EK. Hence the theorem is established.
THEOREM III, PROPOSITION III
In the case of unequal speeds, the time-intervals
required to traverse a given space are to each
other inversely as the speeds.
Let the larger of the two unequal speeds be
indicated by A', the smaller, by B; and let the
motion corresponding to both traverse the given
space CD. Then, I say, the time required to trav-
A" 1
Fig. 41
erse the distance CD at speed A is to the time
required to traverse the same distance at speed
B, as the speed B is to the speed A. For let CD
be to CEas A is to B; then, from the preceding,
it follows that the time required to complete
the distance CD at speed A is the same as the
time necessary to complete CE at speed B', but
the time needed to traverse the distance CE at
speed B is to the time required to traverse the
distance CD at the same speed as CE is to CD;
therefore, the time in which CD is covered at
speed A is to the time in which CD is covered
at speed B as CE is to CD, that is, as speed B is
to speed A. Q. E. D.
THEOREM IV, PROPOSITION IV
If two particles are carried with uniform motion^
but each with a different speed, the distances covered
by them during unequal intervals of time bear to
each other the compound ratio of the speeds and
time intervals.
Let the two particles which are carried with
uniform motion be E and F and let the ratio of
THE TWO NEW SCIENCES
199
the speed of the body £ be to that of the body
F as A is to B; but let the ratio of the time con-
sumed by the motion of E be to the time con-
sumed by the motion of F as C is to D. Then,
I say, that the distance covered by E, with
speed A in time C, bears to the space traversed
by F with speed B in time D a ratio which is the
product of the ratio of the speed A to the speed
B by the ratio of the time C to the time D. For
if G is the distance traversed by E at speed A
E
Fig. 42
during the time-interval C, and if G is to I as
the speed A is to the speed B; and if also the
time-interval C is to the time-interval D as 7 is
to L, then it follows that / is the distance trav-
ersed by F in the same time that G is traversed
by E since G is to / in the same ratio as the speed
A to the speed B. And since / is to L in the same
ratio as the time-intervals C and D, if 7 is the
distance traversed by F during the interval C,
then L will be the distance traversed by F dur-
ing the interval D at the speed B.
But the ratio of G to L is the product of the
ratios G to I and / to L, that is, of the ratios
of the speed A to the speed B and of y,
the time-interval C to the time-in- ^
terval D. Q. E. D. S'
THEOREM V, PROPOSITION V
TO
If two particles are moved at a uniform D ^,
rate, but with unequal speeds, through
unequal distances, then the ratio of the
time-intervals occupied will be the product of the
ratio of the distances by the inverse ratio of the speeds.
Let the two moving particles be denoted by
O
EH
B
Fig- 43
A and B, and let the speed of A be to the speed
of B in the ratio of V to T; in like manner let
the distances traversed be in the ratio of 5 to R\
then, I say, that the ratio of the time-interval
during which the motion of A occurs to the
time-interval occupied by the motion of B is
the product of the ratio of the speed T to the
speed V by the ratio of the distance S to the
distance R.
Let C be the time-interval occupied by the
motion of A, and let the time-interval C bear
to a time-interval E the same ratio as the speed
T to the speed V.
And since C is the time-interval during which
A, with speed V, traverses the distance 5, and
since T, the speed of B, is to the speed V, as
the time-interval C is to the time-interval E,
then E will be the time required by the particle
B to traverse the distance 5. If now we let the
time-interval £ be to the time-interval G as the
distance S is to the distance R, then it follows
that G is the time required by B to traverse the
space R. Since the ratio of C to G is the product
of the ratios C to E and £ to G (while also the
ratio of C to £ is the inverse ratio of the speeds
of A and B respectively, i.e., the ratio of T to
V) ; and since the ratio of £ to G is the same as
that of the distances S and R respectively, the
proposition is proved.
THEOREM VI, PROPOSITION VI
If two particles are carried at a uniform rate, the
ratio of their speeds will be the product of the
ratio of the distances traversed by the inverse ratio
of the time-intervals occupied.
Let A and B be the two particles which move
at a uniform rate; and let the respective dis-
Fig. 44
tances traversed by them have the ratio of V
to T, but let the time-intervals be as S to R.
Then, I say, the speed of A will bear to the speed
of B a ratio which is the product of the ratio
of the distance V to the distance T and the
... -, time- in terval R to the time-interval 5.
Let Cbe the speed at which A traverses
the distance V during the time-interval 5;
and let the speed C bear the same ratio to
another speed E as F bears to T; then £
will be the speed at which B traverses the
distance T during the time-interval 5. If now
the speed £ is to another speed G as the time-
interval R is to the time-interval 5, then G
will be the speed at which the particle B tra-
verses the distance T during the time-inter-
val R. Thus we have the speed C at which
200
the particle A covers the distance V during the
time 5 and also the speed Gat which the par-
ticle B traverses the distance T during the time
R. The ratio of C to G is the product of the ratio
C to E and E to G; the ratio of G to E is by
definition the same as the ratio of the distance
V to distance T; and the ratio of E to G is the
same as the ratio of R to S. Hence follows the
proposition.
SALV. The preceding is what our Author has
written concerning uniform motion. We pass
now to a new and more discriminating con-
sideration of naturally accelerated motion, such
as that generally experienced by heavy falling
bodies; following is the title and introduction.
NATURALLY ACCELERATED MOTION
The properties belonging to uniform motion
have been discussed in the preceding section ; but
accelerated motion remains to be considered.
And first of all it seems desirable to find and
explain a definition best fitting natural phe-
nomena. For anyone may invent an arbitrary
type of motion and discuss its properties; thus,
for instance, some have imagined helices and
conchoids as described by certain motions which
are not met with in nature, and have very com-
mendably established the properties which these
curves possess in virtue of their definitions; but
we have decided to consider the phenomena of
bodies falling with an acceleration such as ac-
tually occurs in nature and to make this defini-
tion of accelerated motion exhibit the essential
features of observed accelerated motions. And
this, at last, after repeated efforts we trust we
have succeeded in doing. In this belief we are
confirmed mainly by the consideration that ex-
perimental results are seen to agree with and ex-
actly correspond with those properties which
have been, one after another, demonstrated by
us. Finally, in the investigation of naturally
accelerated motion we were led, by hand as it
were, in following the habit and custom of na-
ture herself, in all her various other processes,
to employ only those means which are most
common, simple and easy.
For I think no one believes that swimming or
flying can be accomplished in a manner simpler
or easier than that instinctively employed by
fishes and birds.
When, therefore, I observe a stone initially at
rest falling from an elevated position and con-
tinually acquiring new increments of speed, why
should I not believe that such increases take
place in a manner which is exceedingly simple
GALILEO GALILEI
and rather obvious to everybody ? If now we ex-
amine the matter carefully we find no addition
or increment more simple than that which re-
peats itself always in the same manner. This we
readily understand when we consider the inti-
mate relationship between time and motion; for
just as uniformity of motion is defined by and
conceived through equal times and equal spaces
(thus we call a motion uniform when equal dis-
tances are traversed during equal time-inter-
vals), soalso we may, in asimilar manner, through
equal time-intervals, conceive additions of
speed as taking place without complication;
thus we may picture to our mind a motion as
uniformly and continuously accelerated when,
during any equal intervals of time whatever,
equal increments of speed are given to it. Thus,
if any equal intervals of time whatever have
elapsed, counting from the time at which the
moving body left its position of rest and began
to descend, the amount of speed acquired during
the first two time-intervals will be double that
acquired during the first time-interval alone; so
the amount added during three of these time-
intervals will be treble; and that in four, quad-
ruple that of the first time-interval. To put the
matter more clearly, if a body were to continue
its motion with the same speed which it had
acquired during the first time-interval and were
to retain this same uniform speed, then its mo-
tion would be twice as slow as that which it
would have if its velocity had been acquired
during two time-intervals.
And thus, it seems, we shall not be far wrong
if we put the increment of speed as proportional
to the increment of time; hence the definition
of motion which we are about to discuss may be
stated as follows: A motion is said to be uni-
formly accelerated, when starting from rest, it
acquires, during equal time-intervals, equal in-
crements of speed.
SAGR. Although I can offer no rational objec-
tion to this or indeed to any other definition,
devised by any author whomsoever, since all
definitions are arbitrary, I may nevertheless
without offense be allowed to doubt whether
such a definition as the above, established in an
abstract manner, corresponds to and describes
that kind of accelerated motion which we meet
in nature in the case of freely falling bodies.
And since the Author apparently maintains that
the motion described in his definition is that of
freely falling bodies, I would like to clear my
mind of certain difficulties in order that I may
later apply myself more earnestly to the propo-
sitions and their demonstrations.
THE TWO NEW SCIENCES
SALV. It is well that you and Simplicio raise
these difficulties. They are, I imagine, the same
which occurred to me when I first saw this trea-
tise, and which were removed either b^ discus-
sion with the Author himself, or by turning the
matter over in my own mind.
SAGR. When I think of a heavy body falling
from rest, that is, starting with zero speed and
gaining speed in proportion to the time from the
beginning of the motion ; such a motion as would,
for instance, in eight beats of the pulse acquire
eight degrees of speed; having at the end of the
fourth beat acquired four degrees; at the end of
the second, two; at the end of the first, one: and
since time is divisible without limit, it follows
from all these considerations that if the earlier
speed of a body is less than its present speed in a
constant ratio, then there is no degree of speed
however small (or, one may say, no degree of
slowness however great) with which we may not
find this body travelling after starting from in-
finite slowness, /.£., from rest. So that if that
speed which it had at the end of the fourth beat
was such that, if kept uniform, the body would
traverse two miles in an hour, and if keeping
the speed which it had at the end of the second
beat, it would traverse one mile an hour, we
must infer that, as the instant of starting is more
and more nearly approached, the body moves
so slowly that, if it kept on moving at this rate,
it would not traverse a mile in an hour, or in a
day, or in a year or in a thousand years; indeed,
it would not traverse a span in an even greater
time; a phenomenon which baffles the imagina-
tion, while our senses show us that a heavy fall-
ing body suddenly acquires great speed.
SALV. This is one of the difficulties which I
also at the beginning, experienced, but which I
shortly afterwards removed; and the removal
was effected by the very experiment which cre-
ates the difficulty for you. You say the experi-
ment appears to show that immediately after a
heavy body starts from rest it acquires a very
considerable speed: and I say that the same ex-
periment makes clear the fact that the initial
motions of a falling body, no matter how heavy,
are very slow and gentle. Place a heavy body
upon a yielding material, and leave it there with-
out any pressure except that owing to its own
weight; it is clear that if one lifts this body a
cubit or two and allows it to fall upon the same
material, it will, with this impulse, exert a new
and greater pressure than that caused by its mere
weight; and this effect is brought about by the
falling body together with the velocity acquired
during the fall, an effect which will be greater
201
and greater according to the height of the fall,
that is according as the velocity of the falling
body becomes greater. From the quality and in-
tensity of the blow we are thus enabled to ac-
curately estimate the speed of a falling body.
But tell me, gentlemen, is it not true that if a
block be allowed to fall upon a stake from a
height of four cubits and drives it into the
earth, say, four finger- breadths, that coming
from a height of two cubits it will drive the
stake a much less distance, and from the height
of one cubit a still less distance; and finally if
the block be lifted only one finger-breadth how
much more will it accomplish than if merely laid
on top of the stake without percussion ? Cer-
tainly very little. If it be lifted only the thick-
ness of a leaf, the effect will be altogether im-
perceptible. And since the effect of the blow de-
pends upon the velocity of this striking body,
can any one doubt the motion is very slow and
the speed more than small whenever the effect
is imperceptible? See now the power of truth;
the same experiment which at first glance seemed
to show one thing, when more carefully exam-
ined, assures us of the contrary.
But without depending upon the above ex-
periment, which is doubtless very conclusive, it
seems to me that it ought not to be difficult to
establish such a fact by reasoning alone. Imagine
a heavy stone held in the air at rest; the support
is removed and the stone set free; then since it
is heavier than the air it begins to fall, and not
with uniform motion but slowly at the begin-
ning and with a continuously accelerated mo-
tion. Now since velocity can be increased and
diminished without limit, what reason is there
to believe that such a moving body starting
with infinite slowness, that is, from rest, imme-
diately acquires a speed of ten degrees rather
than one of four, or of two, or of one, or of a
half, or of a hundredth; or, indeed, of any of the
infinite number of small values? Pray listen. I
hardly think you will refuse to grant that the
gain of speed of the stone falling from rest fol-
lows the same sequence as the diminution and
loss of this same speed when, by some impelling
force, the stone is thrown to its former eleva-
tion: but even if you do not grant this, I do not
see how you can doubt that the ascending stone,
diminishing in speed, must before coming to
rest pass through every possible degree of slow-
ness.
SIMP. But if the number of degrees of greater
and greater slowness is limitless, they will never
be all exhausted, therefore such an ascending
heavy body will never reach rest, but will con-
202
tinue to move without limit always at a slower
rate; but this is not the observed fact.
SALV. This would happen, Simplicio, if the
moving body were to maintain its speed for any
length of time at each degree of velocity; but it
merely passes each point without delaying more
than an instant: and since each time-interval
however small may be divided into an infinite
number of instants, these will always be suffi-
cient to correspond to the infinite degrees of
diminished velocity.
That such a heavy rising body does not re-
main for any length of time at any given degree
of velocity is evident from the following: be-
cause if, some time-interval having been assigned,
the body moves with the same speed in the last
as in the first instant of that time-interval, it
could from this second degree of elevation be in
like manner raised through an equal height, just
as it was transferred from the first elevation to
the second, and by the same reasoning would
pass from the second to the third and would
finally continue in uniform motion forever.
SAGR. From these considerations it appears to
me that we may obtain a proper solution of the
problem discussed by philosophers, namely,
what causes the acceleration in the natural mo-
tion of heavy bodies ? Since, as it seems to me,
the force impressed by the agent projecting the
body upwards diminishes continuously, this
force, so long as it was greater than the contrary
force of gravitation, impelled the body upwards;
when the two are in equilibrium the body ceases
to rise and passes through the state of rest in
which the impressed impetus is not destroyed,
but only its excess over the weight of the body
has been consumed — the excess which caused
the body to rise. Then as the diminution of the
outside impetus continues, and gravitation gains
the upper hand, the fall begins, but slowly at
first on account of the opposing impetus, a large
portion of which still remains in the body; but
as this continues to diminish it also continues to
be more and more overcome by gravity, hence
the continuous acceleration of motion.
SIMP. The idea is clever, yet more subtle than
sound; for even if the argument were conclu-
sive, it would explain only the case in which a
natural motion is preceded by a violent motion,
in which there still remains active a portion of
the external force; but where there is no such
remaining portion and the body starts from an
anteceSent state of rest, the cogency of the whole
argument fails.
SAGR. I believe that you are mistaken and
that this distinction between cases which you
GALILEO GALILEI
make is superfluous or rather nonexistent. But,
tell me, cannot a projectile receive from the
projector either a large or a small force such as
will throw it to a height of a hundred cubits,
and even twenty or four or one ?
SIMP. Undoubtedly, yes.
SAGR. So therefore this impressed force may
exceed the resistance of gravity so slightly as to
raise it only a finger- breadth; and finally the
force of the projector may be just large enough
to exactly balance the resistance of gravity so
that the body is not lifted at all but merely sus-
tained. When one holds a stone in his hand does
he do anything but give it a force impelling it
upwards equal to the power of gravity drawing
it downwards? And do you not continuously
impress this force upon the stone as long as you
hold it in the hand ? Does it perhaps dimmish
with the time during which one holds the stone ?
And what does it matter whether this support
which prevents the stone from falling is fur-
nished by one's hand or by a table or by a rope
from which it hangs? Certainly nothing at all.
You must conclude, therefore, Simplicio, that
it makes no difference whatever whether the
fall of the stone is preceded by a period of rest
which is long, short, or instantaneous provided
only the fall does not take place so long as the
stone is acted upon by a force opposed to its
weight and sufficient to hold it at rest.
SALV. The present does not seem to be the
proper time to investigate the cause of the ac-
celeration of natural motion concerning which
various opinions have been expressed by various
philosophers, some explaining it by attraction
to the centre, others to repulsion between the
very small parts of the body, while still others
attribute it to a certain stress in the surrounding
medium which closes in behind the falling body
and drives it from one of its positions to an-
other. Now, all these fantasies, and others too,
ought to be examined; but it is not really worth-
while. At present it is the purpose of our Author
merely to investigate and to demonstrate some
of the properties of accelerated motion (what-
ever the cause of this acceleration may be)-—
meaning thereby a motion, such that the mo-
mentum of its velocity goes on increasing after
departure from rest, in simple proportionality
to the time, which is the same as saying that in
equal time-intervals the body receives equal in-
crements of velocity; and if we find the proper-
ties which will be demonstrated later are real-
ized in freely falling and accelerated bodies, we
may conclude that the assumed definition in-
cludes such a motion of falling bodies and that
THE TWO NEW SCIENCES
203
their speed goes on increasing as the time and
the duration of the motion.
SAGR. So far as I see at present, the definition
might have been put a little more clearly per-
haps without changing the fundamental idea,
namely, uniformly accelerated motion is such
that its speed increases in proportion to the space
traversed; so that, for example, the speed ac-
quired by a body in falling four cubits would be
double that acquired in falling two cubits and
this latter speed would be double that acquired
in the first cubit. Because there is no doubt but
that a heavy body falling from the height of six
cubits has, and strikes with, a momentum dou-
ble that it had at the end of three cubits, triple
that which it would have if it had fallen from
two, and sextuple that which it would have
had at the end of one.
SALV. It is very comforting to me to have had
such a companion in error; and moreover let me
tell you that your proposition seems so highly
probable that our Author himself admitted,
when I advanced this opinion to him, that he had
for some time shared the same fallacy. But what
most surprised me was to see two propositions
so inherently probable that they commanded
the assent of everyone to whom they were pre-
sented, proven in a few simple words to be not
only false, but impossible.
SIMP. I am one of those who accept the prop-
osition, and believe that a falling body acquires
force in its descent, its velocity increasing in
proportion to the space, and that the momen-
tum of the falling body is doubled when it falls
from a doubled height; these propositions, it ap-
pears to me, ought to be conceded without hesi-
tation or controversy.
SALV. And yet they are as false and impossible
as that motion should be completed instantane-
ously; and here is a very clear demonstration of
it. If the velocities are in proportion to the spaces
traversed, or to be traversed, then these spaces
are traversed in equal intervals of time; if, there-
fore, the velocity with which the falling body
traverses a space of eight feet were double that
with which it covered the first four feet (just as
the one distance is double the other), then the
time-intervals required for these passages would
be equal. But for one and the same body to fall
eight feet and four feet in the same time is pos-
sible only in the case of instantaneous motion;
but observation shows us that the motion of a
falling body occupies time, and less of it in cov-
ering a distance of four feet than of eight feet;
therefore it is not true that its velocity increases
in proportion to the space.
The falsity of the other proposition may be
shown with equal clearness. For if we consider
a single striking body the difference of momen-
tum in its blows can depend only upon differ-
ence of velocity; for if the striking body falling
from a double height were to deliver a blow of
double momentum, it would be necessary for
this body to strike with a doubled velocity; but
with this doubled speed it would traverse a
doubled space in the same time-interval; obser-
vation however shows that the time required for
fall from the greater height is longer.
SAGR. You present these recondite matters
with too much evidence and ease; this great fa-
cility makes them less appreciated than they
would be had they been presented in a more ab-
struse manner. For, in my opinion, people es-
teem more lightly that knowledge which they
acquire with so little labor than that acquired
through long and obscure discussion.
SALV. If those who demonstrate with brevity
and clearness the fallacy of many popular be-
liefs were treated with contempt instead of grat-
itude the injury would be quite bearable; but
on the other hand, it is very unpleasant and an-
noying to see men, who claim to be peers of any-
one in a certain field of study, take for granted
certain conclusions which later are quickly and
easily shown by another to be false. I do not de-
scribe such a feeling as one of envy, which usual-
ly degenerates into hatred and anger against
those who discover such fallacies; I would call it
a strong desire to maintain old errors, rather
than accept newly discovered truths. This de-
sire at times induces them to unite against these
truths, although at heart believing in them,
merely for the purpose of lowering the esteem
in which certain others are held by the unthink-
ing crowd. Indeed, I have heard from our Acad-
emician many such fallacies held as true but
easily refutable; some of these I have in mind.
SAGR. You must not withhold them from us,
but, at the proper time, tell us about them even
though an extra session be necessary. But now,
continuing the thread of our talk, it would seem
that up to the present we have established the
definitionof uniformly accelerated motion which
is expressed as follows:
A motion is said to be equally or uniformly accel-
erated when, starting from rest, its momentum re-
ceives equal increments in equal times.
SALV. This definition established, the Author
makes a single assumption, namely,
The speeds acquired by one and the same body
moving down planes of different inclinations are
equal when the heights of these planes are equal.
204
GALILEO GALILEI
By the height of an inclined plane we mean
the perpendicular let fall from the upper end of
the plane upon the horizontal line drawn through
the lower end of the same plane. Thus, to illus-
trate, let the line AB be horizontal, and let the
planes CA and CD be inclined to it; then the
Author calls the perpendicular CB the "height"
of the planes CA and CD; he supposes that the
speeds acquired by one and the same body, de-
scending along the planes CA and CD to the
terminal points A and D are equal since the
heights of these planes are the same, CB; and
also it must be understood that this speed is that
which would be acquired by the same body fall-
ing from C to B.
SAGR. Your assumption appears to me so rea-
sonable that it ought to be conceded without
question, provided of course there are no
chance or outside resistances, and that the
planes are hard and smooth, and that the figure
of the moving body is perfectly round, so that
Fig- 45
neither plane nor moving body is rough. ~
All resistance and opposition having —
been removed, my reason tells me at
once that a heavy and perfectly round
ball descending along the lines CA,
CD, CB would reach the terminal points
A, D, B, with equal momenta.
SALV. Your words are very plausible; but I
hope by experiment to increase the probability
to an extent which shall be little short of a
rigid demonstration.
Imagine this page to represent a vertical
wall, with a nail driven into it; and from the
nail let there be suspended a lead bullet of one
or two ounces by means of a fine vertical thread,
AB, say from four to six feet long; on this wall
draw a horizontal line DC, at right angles to
the vertical thread AB, which hangs about two
finger- breadths in front of the wall. Now bring
the thread AB with the attached ball into the
position AC and set it free; first it will be ob-
served to descend along the arc CBD, to pass
the point B, and to travel along the arc BD, till
it almost reaches the horizontal CD, a slight
shortage being caused by the resistance of the
air and the string; from this we may rightly in-
fer that the ball in its descent through the arc
CB acquired a momentum on reaching B,
which was just sufficient to carry it through a
similar arc BD to the same height. Having re-
peated this experiment many times, let us now
drive a nail into the wall close to the perpendic-
ular AB, say at E or F, so that it projects out
some five or six finger-breadths in order that
the thread, again carrying the bullet through
the arc CB, may strike upon the nail E when
the bullet reaches B, and thus compel it to
traverse the arc BG, described about E as cen-
tre. From this we can see what can be done by
the same momentum which previously start-
ing at the same point B carried the same body
through the arc BD to the horizontal CD.
Now, gentlemen, you will observe with pleas-
ure that the ball swings to the point G in the
horizontal, and you would see the same thing
happen if the obstacle were placed at some low-
er point, say at F, about which the ball would
Fig. 46
describe the arc BI, the rise of the ball always
terminating exactly on the line CD. But when
the nail is placed so low that the remainder of
the thread below it will not reach to the height
CD (which would happen if the nail were
placed nearer B than to the intersection of AB
with the horizontal CD), then the thread leaps
over the nail and twists itself about it.
This experiment leaves no room for doubt
as to the truth of our supposition; for since the
two arcs CB and DB are equal and similarly
placed, the momentum acquired by the fall
through the arc CB is the same as that gained
by fall through the arc DB: but the momentum
acquired at B, owing to fall through CB, is able
to lift the same body through the arc BD',
therefore, the momentum acquired in the fall
BD is equal to that which lifts the same body
through the same arc from B to D; so, in gen-
THE TWO NEW SCIENCES
205
eral, every momentum acquired by fall through
an arc is equal to that which can lift the same
body through the same arc. But all these mo-
menta which cause a rise through the arcs BD,
BG, and El are equal, since they are produced
by the same momentum, gained by fall through
CB, as experiment shows. Therefore all the mo-
menta gained by fall through the arcs DB, GB,
IB are equal.
SAGR. The argument seems to me so conclu-
sive and the experiment so well adapted to es-
tablish the hypothesis that we may, indeed,
consider it as demonstrated.
SALV. I do not wish, Sagredo, that we trouble
ourselves too much about this matter, since we
are going to apply this principle mainly in mo-
tions which occur on plane surfaces, and not
upon curved, along which acceleration varies
in a manner greatly different from that which
we have assumed for planes.
So that, although the above experiment
shows us that the descent of the moving body
through the arc CB confers upon it momentum
just sufficient to carry it to the same height
through any of the arcs BD, BG, BI, we are not
able, by similar means, to show that the event
would be identical in the case of a perfectly
round ball descending along planes whose in-
clinations are respectively the same as the
chords of these arcs. It seems likely, on the
other hand, that, since these planes form angles
at the point B, they will present an obstacle to the
ball which has descended along the chord CB,
and starts to rise along the chord BD, BG, BI.
In striking these planes some of its momen-
tum will be lost and it will not be able to rise to
the height of the line CD; but this obstacle,
which interferes with the experiment, once re-
moved, it is clear that the momentum (which
gains in strength with descent) will be able to
carry the body to the same height. Let us then,
for the present, take this as a postulate, the ab-
solute truth of which will be established when
we find that the inferences from it correspond
to and agree perfectly with experiment. The
Author having assumed this single principle
passes next to the propositions which he clearly
demonstrates; the first of these is as follows:
THEOREM I, PROPOSITION I
The time in which any space is traversed by a body
starting from rest and uniformly accelerated, is
equal to the time in which that same space would
be traversed by the same body moving at a uniform
speed whose value is the mean of the highest speed
and the speed just before acceleration began.
Let us represent by the line AB the time in
which the space CD is traversed by a body
which starts from rest at Cand is uniformly ac-
celerated; let the final and highest value of the
speed gained during the interval AB be rep-
resented by the line EB drawn at right angles
to AB; draw the line AE, then all lines drawn
from equidistant points on AB and parallel to
BE will represent the in- r
creasing values of the speed,
beginning with the instant
A. Let the point F bisect
the line EB; draw FG par-
allel to BA, and GA parallel
to FB, thus forming a par-
allelogram AGFB which
will be equal in area to the
triangle AEB, since the side
GF bisects the side AE at
the point /; for if the paral-
lel lines in the triangle AEB
are extended to GI, then
the sum of all the parallels
contained in the quadrila-
teral is equal to the sum of
those contained in the tri-
angle AEB\ for those in the
triangle IEF are equal to
those contained in the tri- '
angle GIA, while those included in the trape-
zium AIFB are common. Since each and every
instant of time in the time-interval AB has its
corresponding point on the line AB, from which
points parallels drawn in and limited by the
triangle AEB represent the increasing values of
the growing velocity, and since parallels con-
tained within the rectangle represent the val-
ues of a speed which is not increasing, but con-
stant, it appears, in like manner, that the mo-
menta assumed by the moving body may also
be represented, in the case of the accelerated
motion, by the increasing parallels of the tri-
angle AEB, and, in the case of the uniform mo-
tion, by the parallels of the rectangle GB. For,
what the momenta may lack in the first part of
the accelerated motion (the deficiency of the
momenta being represented by the parallels of
the triangle AGI) is made up by the momenta
represented by the parallels of the triangle IEF.
Hence it is clear that equal spaces will be
traversed in equal times by two bodies, one of
which, starting from rest, moves with a uni-
form acceleration, while the momentum of the
other, moving with uniform speed, is one-half
its maximum momentum under accelerated mo-
tion.
Q. £. D.
206
GALILEO GALILEI
B Jl
Fig. 48
THEOREM II, PROPOSITION II
The spaces described by a body falling from rest
with a uniformly accelerated motion are to each
other as the squares of the time- intervals em-
ployed in traversing these distances.
Let the time beginning with any instant A be
represented by the straight line AB in which
are taken any two time -intervals AD and AE.
Let HI represent the distance through which
the body, starting from rest at H, falls with
uniform acceleration. If HL represents the
space traversed during the time-interval AD,
and HM that covered during the interval AE,
then the space MH stands to the space LH in a
ratio which is the square of the ratio of the
time AE to the time AD', or we may say sim-
ply that the distances HM and HL are related
as the squares of AE and AD.
Draw the line AC making any angle what-
ever with the line AB; and from the points D
and E, draw the parallel lines DO and EP; of
these two lines, DO represents the greatest
velocity attained during the interval AD, while
EP represents the maximum velocity acquired
during the interval AE. But it has just been
proved that so far as distances traversed are
concerned it is precisely the same whether a
body falls from rest with a uniform accelera-
tk>n or whether it falls during an equal time-
interval with a constant speed which is one-
half the maximum speed attained during the
accelerated motion. It follows therefore that
the distances HM and HL are the same as
would be traversed, during the time-intervals
AE and AD, by uniform velocities equal to
one-half those represented by DO and EP re-
spectively. If, therefore, one can show that the
distances HM and HL are in the same ratio as
the squares of the time-intervals AE and AD,
our proposition will be proven.
But in the fourth proposition of the first
book [p. 198 above] it has been shown that the
spaces traversed by two particles in uniform
motion bear to one another a ratio which is
equal to the product of the ratio of the veloci-
ties by the ratio of the times. But in this case
the ratio of the velocities is the same as the ra-
tio of the time-intervals (for the ratio of AE to
AD is the same as that of ]4 EP to J^DO or of
EP to DO). Hence the ratio of the spaces trav-
ersed is the same as the squared ratio of the
time-intervals. Q. E. D.
Evidently then the ratio of the distances is
the square of the ratio of the final velocities,
that is, of the lines EP and DO, since these are
to each other as AE to AD.
COROLLARY I
Hence it is clear that if we take any equal in-
tervals of time whatever, counting from the be-
ginning of the motion, such as AD, DE, EF,
FG, in which the spaces HL, LM, MN, NI are
traversed, these spaces will bear to one another
the same ratio as the series of odd numbers, i,
3, 5, 7; for this is the ratio of the differences of
the squares of the lines, differences which ex-
ceed one another by equal amounts, this ex-
cess being equal to the smallest line: or we
may say of the differences of the squares of the
natural numbers beginning with unity.
While, therefore, during equal intervals of
time the velocities increase as the natural num-
bers, the increments in the distances traversed
during these equal time-intervals are to one an-
other as the odd numbers beginning with unity.
SAGR. Please suspend the discussion for a mo-
ment since there just occurs to me an idea which
I want to illustrate by means of a diagram in or-
der that it may be clearer both to you and to
me.
Let the line Al represent the lapse of time
measured from the initial instant A', through A
draw the straight line AF making any angle
whatever; join the terminal points / and F\
divide the time Al in half at C; draw CB par-
THE TWO NEW SCIENCES
207
D ;
N
H
O
49
allel to IF. Let us consider CB as the maximum
value of the velocity which increases from zero
at the beginning, in simple proportionality to
the intercepts on the triangle ABC of lines
drawn parallel to BC; or what is the same
thing, let us suppose the velocity to increase in
proportion to the time; then I admit without
question, in view of the preceding argument,
that the space described by a body falling in
the aforesaid manner will be equal to the space
traversed by the same body during the same
length of time travelling with a uniform speed
equal to EC, the half of EC. Further let us ima-
gine that the body has fallen with accelerated
motion so that, at the instant C, it has the
velocity BC. It is clear that if the body con-
tinued to descend with the same speed BC,
without acceleration, it would in the next time-
interval CI traverse double the distance cov-
ered during the interval AC, with the uniform
speed EC which is half of BC', but since the
falling body acquires equal increments of speed
during equal increments of time, it follows that
the velocity BC> during the next time-interval
CI will be increased by an amount represented
by the parallels of the triangle BFG which is
equal to the triangle ABC. If, then, one adds to
the velocity GI half of the velocity FG, the
highest speed acquired by the accelerated mo-
tion and determined by the parallels of the
triangle BFG, he will have the uniform velocity
with which the same space would have been
described in the time C7; and since this speed
IN is three times as great as EC it follows that
the space described during the interval CI is
three times as great as that described during
the interval AC. Let us imagine the motion ex-
tended over another equal time-interval 7O,
and the triangle extended to APO\ it is then
evident that if the motion continues during
the interval 7O, at the constant rate IF ac-
quired by acceleration during the time Al, the
space traversed during the interval 10 will be
four times that traversed during the first inter-
val AC, because the speed IF is four times the
speed EC. But if we enlarge our triangle so as to
include FPQ which is equal to ABC, still assum-
ing the acceleration to be constant, we shall
add to the uniform speed an increment RQ,
equal to EC', then the value of the equivalent
uniform speed during the time-interval 70 will
be five times that during the first time-interval
AC\ therefore the space traversed will be quin-
tuple that during the first interval AC. It is
thus evident by simple computation that a
moving body starting from rest and acquiring
velocity at a rate proportional to the time, will,
during equal intervals of time, traverse dis-
tances which are related to each other as the
odd numbers beginning with unity, i, 3, 5; or
considering the total space traversed, that cov-
ered in double time will be quadruple that cov-
ered during unit time; in triple time, the space
is nine times as great as in unit time. And in
general the spaces traversed are in the duplicate
ratio of the times, i.e., in the ratio of the squares
of the times.
SIMP. In truth, I find more pleasure in this
simple and clear argument of Sagredo than in
the Author's demonstration which to me ap-
pears rather obscure; so that I am convinced
that matters are as described, once having ac-
cepted the definition of uniformly accelerated
motion. But as to whether this acceleration is
that which one meets in nature in the case of
falling bodies, I am still doubtful; and it seems
to me, not only for my own sake but also for all
those who think as I do, that this would be the
proper moment to introduce one of those ex-
periments— and there are many of them, I un-
derstand—which illustrate in several ways the
conclusions reached.
SALV. The request which you, as a man of
science, make, is a very reasonable one; for this
is the custom — and properly so — in those sci-
ences where mathematical demonstrations are
applied to natural phenomena, as is seen in the
case of perspective, astronomy, mechanics, mu-
sic, and others where the principles, once es-
tablished by well-chosen experiments, become
208
GALILEO GALILEI
the foundations of the entire superstructure. I
hope therefore it will not appear to be a waste
of time if we discuss at considerable length this
first and most fundamental question upon
which hinge numerous consequences of which
we have in this book only a small number,
placed there by the Author, who has done so
much to open a pathway hitherto closed to
minds of speculative turn. So far as experiments
go they have not been neglected by the Author;
and often, in his company, I have attempted in
the following manner to assure myself that the
acceleration actually experienced by falling
bodies is that above described.
A piece of wooden moulding or scantling,
about 12 cubits long, half a cubit wide, and
three finger-breadths thick, was taken; on its
edge was cut a channel a little more than one
finger in breadth; having made this groove very
straight, smooth, and polished, and having
lined it with parchment, also as smooth and
polished as possible, we rolled along it a hard,
smooth, and very round bronze ball. Having
placed this board in a sloping position, by lift-
ing one end some one or two cubits above the
other, we rolled the ball, as I was just saying,
along the channel, noting, in a manner present-
ly to be described, the time required to make
the descent. We repeated this experiment more
than once in order to measure the time with an
accuracy such that the deviation between two
observations never exceeded one-tenth of a
pulse-beat. Having performed this operation
and having assured ourselves of its reliability,
we now rolled the ball only one-quarter the
length of the channel; and having measured
the time of its descent, we found it precisely
one-half of the former. Next we tried other dis-
tances, comparing the time for the whole
length with that for the half, or with that for
two-thirds, or three-fourths, or indeed for any
fraction; in such experiments, repeated a full
hundred times, we always found that the spaces
traversed were to each other as the squares of
the times, and this was true for all inclinations
of the plane, i.e., of the channel, along which
we rolled the ball. We also observed that the
times of descent, for various inclinations of the
plane, bore to one another precisely that ratio
which, as we shall see later, the Author had
predicted and demonstrated for them.
For the measurement of time, we employed
a large vessel of water placed in an elevated
position; to the bottom of this vessel was sold-
ered a pipe of small diameter giving a thin jet
of water, which we collected in a small glass
during the time of each descent, whether for
the whole length of the channel or for a part of
its length; the water thus collected was
weighed, after each descent, on a very accurate
balance; the differences and ratios of these
weights gave us the differences and ratios of the
times, and this with such accuracy that al-
though the operation was repeated many,
many times, there was no appreciable discrep-
ancy in the results.
SIMP. I would like to have been present at
these experiments; but feeling confidence in
the care with which you performed them, and
in the fidelity with which you relate them, I am
satisfied and accept them as true and valid.
SALV. Then we can proceed without dis-
cussion.
COROLLARY II
Secondly, it follows that, starting from any
initial point, if we take any two distances,
traversed in any time -intervals whatsoever,
these time-intervals bear to one another the
same ratio as one of the distances to the mean
proportional of the two distances.
For if we take two distances ST and 5 Y 0
measured from the initial point S, the
mean proportional of which is SX, the
time of fall through ST is to the time of
fall through SY as ST is to SX\ or one
may say the time of fall through SY is to
the time of fall through STas SYis to SX.
Now since it has been shown that the
spaces traversed are in the same ratio as the
squares of the times; and since, moreover,
the ratio of the space SY to the space ST
is the square of the ratio SY to SX, it fol-
lows that the ratio of the times of fall
through SY and ST is the ratio of the re-
spective distances SYand SX.
SCHOLIUM
The above corollary has been proven for the
case of vertical fall; but it holds also for planes
inclined at any angle; for it is to be assumed
that along these planes the velocity increases in
the same ratio, that is, in proportion to the
time, or, if you prefer, as the series of natural
numbers.
[The dialogue which intervenes between this
Scholium and the following theorem was elaborated
by Viviani, at the suggestion of Galileo. TRANS.]
SALV. Here, Sagredo, I should like, if it be not too
tedious to Simplicio, to interrupt for a moment the
present discussion in order to make some additions
Y
Fig.
5°
THE TWO NEW SCIENCES
209
on the basis of what has already been proved and of
what mechanical principles we have already learned
from our Academician. This addition I make for the
better establishment on logical and experimental
grounds, of the principle which we have above con-
sidered; and what is more important, for the pur-
pose of deriving it geometrically, after first demon-
strating a single lemma which is fundamental in the
science of motion.
SAGR. If the advance which you propose to make
is such as will confirm and fully establish these scien-
ces of motion, I will gladly devote to it any length
of time. Indeed, I shall not only be glad to have you
proceed, but I beg of you at once to satisfy the curi-
osity which you have awakened in me concerning
your proposition; and I think that Simphcio is of
the same mind.
SIMP. Quite right.
SALV. Since then I have your permission, let us
first of all consider this notable fact, that the mo-
menta or speeds of one and the same moving body
vary with the inclination of the plane.
The speed reaches a maximum along a vertical di-
rection, and for other directions diminishes as the
plane diverges from the vertical. Therefore the im-
petus, ability, energy, or, one might say, the momen-
tum of descent of the moving body is diminished by
the plane upon which it is supported and along
which it rolls.
For the sake of greater clearness erect the line AB
perpendicular to the horizontal AC', next draw AD,
AE, AF, etc., at different inclinations to the hori-
zontal. Then I say that all the momentum of the
falling body is along the vertical and is a maximum
when it falls in that direction; the momentum is less
along DA and still less along EA, and even less yet
along the more inclined plane FA. Finally on the
C
Fig. 51
horizontal plane the momentum vanishes altogether;
the body finds itself in a condition of indifference as
to motion or rest; has no inherent tendency to move
in any direction, and offers no resistance to being
set in motion. For just as a heavy body or system of
bodies cannot of itself move upwards, or recede
from the common centre toward which all heavy
things tend, so it is impossible for any body of its
own accord to assume any motion other than one
which carries it nearer to the aforesaid common
centre. Hence, along the horizontal, by which we
understand a surface, every point of which is equi-
distant from this same common centre, the body
will have no momentum whatever.
This change of momentum being clear, it is here
necessary for me to explain something which our
Academician wrote when in Padua, embodying it
in a treatise on mechanics prepared solely for the
use of his students, and proving it at length and con-
clusively when considering the origin and nature of
that marvellous machine, the screw. What he
proved is the manner in which the momentum varies
with the inclination of the plane, as for instance that
of the plane FA, one end of which is elevated
through a vertical distance PC. This direction FC is
that along which the momentum of a heavy body
becomes a maximum; let us discover what ratio this
momentum bears to that of the same body moving
along the inclined plane FA. This ratio, I say, is the
inverse of that of the aforesaid lengths. Such is the
lemma preceding the theorem which I hope to
demonstrate a little later.
It is clear that the impelling force acting on a
body in descent is equal to the resistance or least
force sufficient to hold it at rest. In order to measure
this force and resistance I propose to use the weight
of another body. Let us place upon the plane FA a
body G connected to the weight H by means of a
cord passing over the point F; then the body H will
ascend or descend, along the perpendicular, the
same distance which the body G ascends or descends
along the inclined plane FA\ but this distance will
not be equal to the rise or fall of G along the verti-
cal in which direction alone G, as other bodies, ex-
erts its force. This is clear. For if we consider the
motion of the body G, from A to F, in the triangle
AFC to be made up of a horizontal component AC
and a vertical component CF, and remember that
this body experiences no resistance to motion along
the horizontal (because by such a motion the body
neither gams nor loses distance from the common
centre of heavy things), it follows that resistance is
met only in consequence of the body rising through
the vertical distance CF. Since then the body G in
moving from A to F offers resistance only in so far
as it rises through the vertical distance CF, while the
other body H must fall vertically through the en-
tire distance FA, and since this ratio is maintained
whether the motion be large or small, the two bodies
being inextensibly connected, we are able to assert
positively that, in case of equilibrium (bodies at
rest) the momenta, the velocities, or their tend-
ency to motion i.e., the spaces which would be trav-
ersed by them in equal times, must be in the in-
verse ratio to their weights. This is what has been
demonstrated in every case of mechanical motion.
So that, in order to hold the weight G at rest, one
must give H a weight smaller in the same ratio as
the distance CF is smaller than FA. If we do this,
FA:FC=s weight G: weight H', then equilibrium will
occur, that is, the weights H and G will have the
same impelling forces, and the two bodies will come
to rest.
210
GALILEO GALILEI
And since we arc agreed that the impetus, energy,
momentum or tendency to motion of a moving
body is as great as the force or least resistance suffici-
ent to stop it, and since we have found that the
weight H is capable of preventing motion in the
weight G, it follows that the less weight H whose en-
tire force is along the perpendicular, FC, will be an
exact measure of the component of force which the
larger weight G exerts along the plane FA. But the
measure 01 the total force on the body G is its own
weight, since to prevent its fall it is only necessary
to balance it with an equal weight, provided this
second weight be free to move vertically; therefore
the component of the force on G along the inclined
plane FA will bear to the maximum and total force
on this same bodv G along the perpendicular FC
the same ratio as me weight H to the weight G. This
ratio is, by construction, the same which the height
FC, of the inclined plane bears to the length FA. We
have here the lemma which I proposed to demon-
strate and which, as you will see, has been assumed
by our Author in the second part of the sixth propo-
sition of the present treatise.
SAGR. From what you have shown thus far, it ap-
pears to me that one might infer, arguing ex aequali
con la proportion perturbata, that the tendencies of
one and the same body to move along planes differ-
ently inclined, but having the same vertical height,
as FA and F/, are to each other inversely as the
lengths of the planes.
SALV. Perfectly right. This point established, I
pass to the demonstration of the following theorem:
If a body falls freely along smooth planes inclined
at any angle whatsoever, but of the same height, the
speeds with which it reaches the bottom are the same.
First we must recall the fact that on a plane of any
inclination whatever a body starting from rest gains
speed or momentum in direct proportion to the
time, in agreement with the definition of naturally
accelerated motion given by the Author. Hence, as
he has shown in the preceding proposition, the dis-
tances traversed are proportional to the squares of
the times and therefore to the squares of the speeds.
The speed relations are here the same as in the mo-
tion first studied, since in each case the gain of speed
is proportional to the time.
Let AB be an inclined plane whose height above
the level EC is AC. As we have seen above the force
impelling a body to fall along the vertical AC is to
r
Fig. 52
the force which drives the same body along the in-
clined plane AB as AB is to AC. On the incline AB,
lay off AD a third proportional to AB and AC\ then
the force producing motion along AC is to that
along AB (i.e., along AD) as the length AC is to
the length AD. And therefore the body will trav-
erse the space AD, along the incline AB, in the
same time which it would occupy in falling the ver-
tical distance AC, (since the forces are in the same
ratio as these distances) ; also the speed at Cis to the
speed at D as the distance AC is to the distance AD.
But, according to the definition of accelerated mo-
tion, the speed at B is to the speed of the same body
at D as the time required to traverse AB is to the
time required for AD\ and, according to the last
corollary of the second proposition, the time of pass-
ing through the distance AB bears to the time of
passing through AD the same ratio as the distance
AC (a mean proportional between AB and AD) to
AD. Accordingly the two speeds at B and C each
bear to the speed at D the same ratio, namely, that
of the distances AC and AD; hence they are equal.
This is the theorem which I set out to prove.
From the above we are better able to demon-
strate the following third proposition of the Author
in which he employs the following principle, name-
ly, the time required to traverse an inclined plane
is to that required to fall through the vertical
height of the plane in the same ratio as the length
of the plane to its height.
For, according to the second corollary of the sec-
ond proposition, if BA represents the time required
to pass over the distance BA, the time required to
pass the distance AD will be a mean proportional
between these two distances and will be represented
by the line AC] but if AC represents the time need-
ed to traverse AD it will also represent the time re-
quired to fall through the distance AC, since the
distances AC and AD are traversed in equal times;
consequently, if AB represents the time required
for AB then AC will represent the time required
for AC. Hence the times required to traverse A Band
AC are to each other as the distances AB and AC.
In like manner, it can be shown that the time re-
quired to fall through AC is to the time required for
any other incline AE as the length AC is to the
length AE', therefore, ex aequali, the time of fall
along the incline AB is to that along AE as the dis-
tance AB is to the distance AE, etc.
One might by application of this same theorem,
as Sagredo will readily see, immediately demon-
strate the sixth proposition of the Author; but let
us here end this digression which Sagredo has per-
haps found rather tedious, though I consider it quite
important for the theory of motion.
SAGR. On the contrary, it has given me great satis-
faction, and indeed I find it necessary for a complete
grasp of this principle.
SALV. I will now resume the reading of the text.
THEOREM III, PROPOSITION III
If one and the same body, starting from rest, falls
along an inclined plane and also along a vertical,
each having the same height, the times of descent
THE TWO NEW SCIENCES
will be to each other as the lengths of the inclined
plane and the vertical.
Let AC be the inclined plane and AB the per-
pendicular, each having the same vertical height
above the horizontal, namely, BA; then, I say,
the time of descent of one and the same body
along the plane AC bears a ratio to the time of
fall along the perpendicular AB, which is the
same as the ratio of the length AC to the length
AB. Let DG, El and LF be any lines parallel
A
M
Fig- 53
to the horizontal CB', then it follows from what
has preceded that a body starting from A will
acquire the same speed at the point G as at D,
since in each case the vertical fall is the same; in
like manner the speeds at 7 and E will be the
same; so also those at L and F. And in general
the speeds at the two extremities of any parallel
drawn from any point on AB to the correspond-
ing point on AC will be equal.
Thus the two distances AC and AB are trav-
ersed at the same speed. But it has already been
proved that if two distances are traversed by a
body moving with equal speeds, then the ratio
of the times of descent will be the ratio of the
distances themselves; therefore, the time of de-
scent along AC is to that along AB as the length
of the plane AC is to the vertical distance AB.
Q. E. D.
SAGR. It seems to me that the above could
have been proved clearly and briefly on the
basis of a proposition already demonstrated,
namely, that the distance traversed in the case
of accelerated motion along AC or AB is the
same as that covered by a uniform speed whose
value is one-half the maximum speed, CB; the
two distances AC and AB having been trav-
ersed at the same uniform speed it is evident,
from Proposition I, that the times of descent
will be to each other as the distances.
COROLLARY
Hence we may infer that the times of descent
along planes having different inclinations, but
the same vertical height stand to one another
21
in the same ratio as the lengths of the plane:
For consider any plane AM extending from .
to the horizontal CB; then it may be demor
strated in the same manner that the time of d(
scent along AM is to the time along AB as th
distance AM is to AB\ but since the time alon
AB is to that along AC as the length AB is t
the length AC, it follows, ex xquali, that 2
AM is to AC so is the time along AM to th
time along AC.
THEOREM IV, PROPOSITION IV
The times of descent along f lanes of the saw
length but of different inclinations are to each othi
in the inverse ratio of the square roots of the
heights.
From a single point B draw the planes B*
and BC, having the same length but differer
inclinations; let AEand CD be horizontal line
drawn to meet the perpendicular BD', and k
BE represent the height of the plane AB, an
BD the height of BC\ also let BI be a mean prc
portional to BD and BE; then the ratio of Bl
Fig- 54
to BI is equal to the square root of the ratio (
BD to BE. Now, I say, the ratio of the times (
descent along BA and EC is the ratio of BD t
BI; so that the time of descent along BA is r<
lated to the height of the other plane BC, name!
BD as the time along BC is related to the heigfr
BI. Now it must be proved that the time of d<
scent along BA is to that along BCas the lengt
BD is to the length BI.
Draw IS parallel to DC; and since it has bee
shown that the time of fall along BA is to ths
along the vertical BE as BA is to BE; and als
that the time along BE is to that along BD '<
BE is to BI; and likewise that the time alon
BD is to that along BC as BD is to BC, or as I
to BS; it follows, ex aequali, that the time alon
BA is to that along BC as BA to BS, or BC t
BS. However, BC is to BS as BD is to BI; henc
follows our proposition.
212
GALILEO GALILEI
55
THEOREM V, PROPOSITION V
The times of descent along planes of different
length, slope and height bear to one another a ratio
which is equal to the product of the ratio of the
lengths by the square root of the inverse ratio of
their heights.
Draw the planes AB and AC, having differ-
ent inclinations, lengths, and heights. My theo-
A rem then is that the ratio
of the time of descent
along AG to that along
AB is equal to the product
of the ratio of AC to AB
by the square root of the
inverse ratio of their
heights.
For let AD be a per-
pendicular to which are
drawn the horizontal lines
EG and CD; also let AL
be a mean proportional to
JD the heights AGztid AD;
from the point L draw a
horizontal line meeting AC in F; accordingly
AF will be a mean proportional between AC
and AE. Now since the time of descent along
AC is to that along AE as the length AF is to
AE; and since the time along AE is to that along
ABzs AE is to AB, it is clear that the time along
AC is to that along AB as AF is to AB.
Thus it remains to be shown that the ratio of
AF to AB is equal to the product of the ratio of
AC to AB by the ratio of AG to AL, which is
the inverse ratio of the square roots of the
heights DA and GA. Now it is evident that, if
we consider the line AC in connection with AF
and AB, the ratio of AF to AG is the same as
that of AL to AD, or AG to AL which is the
square root of the ratio of the heights AG and
AD; but the ratio of AC to AB is the ratio of
the lengths themselves. Hence follows the
theorem.
THEOREM VI, PROPOSITION VI
If from the highest or lowest point in a vertical
circle there be drawn any inclined planes meeting
the circumference the times of descent along these
chords are each equal to the other.
On the horizontal line GH construct a ver-
tical circle. From its lowest point— the point of
tangency with the horizontal — draw the diam-
eter FA and from the highest point, A, draw
inclined planes to B and C, any points what-
ever on the circumference; then the times of
descent along these are equal. Draw BD and CE
B
H
perpendicular to the diameter; make Ala mean
proportional between the heights of the planes,
AE and AD; and since the rectangles FA.AE
and FA . AD art respectively equal to the squares
of AC and AB, while the rectangle FA.AE is to
the rectangle FA . AD as AE is to AD, it follows
that the square of AC is to the square of AB as
the length AE is to the length AD. But since
the length AE is to AD as the square of Al is to
the square of AD, it follows that the squares on
the lines AC and AB are to each other as the
squares on the lines Al and AD, and hence also
the length AC is to the length AB as Al is to
AD. But it has previously been demonstrated
that the ratio of the time of descent along AC
to that along AB is equal to the product of the
two ratios AC to AB and AD to Al; but this
last ratio is the same as that of AE to AC. There-
fore, the ratio of the time of descent along AC
to that along AE is the product of the two ra-
tios, AC to AE and AE to AC. The ratio of
these times is therefore unity. Hence follows
our proposition.
By use of the principles of mechanics one
may obtain the same result, namely, that a fall-
ing body will require equal times to traverse
the distances CA and DA, indicated in the fol-
lowing figure. Lay off BA equal to DA, and let
fall the perpendiculars BE and DF; it follows
from the principles of mechanics that the com-
ponent of the momentum acting along the in-
clined plane ABC is to the total momentum as
BE is to BA', in like manner the momentum
along the plane AD is to its total momentum as
DF is to DA, or to BA. Therefore the momen-
tum of this same weight along the plane DA is
to that along the plane ABC as the length DF
is to the length BE; for this reason, this same
weight will in equal times according to the sec-
ond proposition of the first book, traverse spaces
TOE TWO NEW SCIENCES
213
along the planes CA and DA which are to each
other as the lengths BE and DP. But it can be
shown that CA is to DA as BE is to DF. Hence
the falling body will traverse the two paths CA
and DA in equal times.
Moreover the fact that CA is to DA as BE
is to DF may be demonstrated as follows: Join
Cand D; through D, draw the line DGL paral-
lel to AFand cutting the line AC in. /; through
B draw the line BH, also parallel to AF. Then
the angle ADI will be equal to the angle DC A,
since they subtend equal arcs LA and DA, and
since the angle DAC is common, the sides of
the triangles, CAD and DAI, about the com-
mon angle will be proportional to each other;
accordingly as CA is to DA so is DA to I A, that
is as BA is to IA, or as HA is to GA, that is as
BE is to DF. Q. E. D.
The same proposition may be more easily
demonstrated as follows: On the horizontal line
AB draw a circle whose diameter DC is vertical.
From the upper end of this diameter draw any
inclined plane, DF, extending to meet the cir-
Fig. 58
cumference; then, I say, a body will occupy the
same time in falling along the plane DFas along
the diameter DC. For draw FG parallel to AB
and perpendicular to DC; join FC; and since
the time of fell along DC is to that along DG as
the mean proportional between CD and GD is
to GD itself; and since also DF is a mean pro-
portional between DC and DG, the angle DFC
inscribed in a semicircle being a right-angle,
and FG being perpendicular to DC, it follows
that the time of fall along DC is to that along
DG as the length FD is to GD. But it has al-
ready been demonstrated that the time of de-
scent along DF is to that along DG as the length
DF is to DG; hence the times of descent along
DF and DC each bear to the time of fell along
DG the same ratio; consequently they are equal.
In like manner it may be shown that if one
draws the chord CE from the lower end of the
diameter, also the line EH parallel to the hori-
zon, and joins the points E and D, the time of
descent along EC, will be the same as that along
the diameter, DC.
COROLLARY I
From this it follows that the times of descent
along all chords drawn through either C or D
are equal one to another.
COROLLARY II
It also follows that, if from any one point
there be drawn a vertical line and an inclined
one along which the time of descent is the
same, the inclined line will be a chord of a semi-
circle of which the vertical line is the diameter.
COROLLARY III
Moreover, the times of descent along inclined
planes will be equal when the vertical heights
of equal lengths of these planes are to each
other as the lengths of the planes themselves;
thus it is clear that the times of descent along
CA and DA, in the figure just before the last,
are equal, provided the vertical height of AB
(AB being equal to AD), namely, BE, is to the
vertical height DF as CA is to DA.
SAGR. Please allow me to interrupt the lec-
ture for a moment in order that I may clear up
an idea which just occurs to me; one which, if
it involve no fallacy, suggests at least a freakish
and interesting circumstance, such as often
occurs in nature and in the realm of necessary
consequences.
214
GALILEO GALILEI
If, from any point fixed in a horizontal plane,
straight lines be drawn extending indefinitely
in all directions, and if we imagine a point to
move along each of these lines with constant
speed, all starting from the fixed point at the
same instant and moving with equal speeds,
then it is clear that all of these moving points
will lie upon the circumference of a circle which
grows larger and larger, always having the afore-
said fixed point as its centre; this circle spreads
out in precisely the same manner as the little
waves do in the case of a pebble allowed to drop
into quiet water, where the impact of the stone
starts the motion in all directions, while the
point of impact remains the centre of these
ever-expanding circular waves. But imagine a
vertical plane from the highest point of which
are drawn lines inclined at every angle and ex-
tending indefinitely; imagine also that heavy
particles descend along these lines each with a
naturally accelerated motion and each with a
speed appropriate to the inclination of its line.
If these moving particles are always visible,
what will be the locus of their positions at any
instant? Now the answer to this question sur-
prises me, for I am led by the preceding theo-
rems to believe that these particles will always
lie upon the circumference of a single circle,
ever increasing in size as the particles recede
farther and farther from the point at which
their motion began. To be more definite, let A
be the fixed point from which are drawn the
lines AF and AH inclined at any angle whatso-
ever. On the perpendicular AB take any two
points Cand D about which, as centres, circles
are described passing through the point A,
and cutting the inclined lines at the points F,
//, B, E, G, /. From the preceding theorems it
59
is clear that, if particles start, at the same in-
stant, from A and descend along these lines,
when one is at E another will be at G and an-
other at /; at a later instant they will be found
simultaneously at F, Hand J5; these, and indeed
an infinite number of other particles travelling
along an infinite number of different slopes will
at successive instants always lie upon a single
ever-expanding circle. The two kinds of motion
occurring in nature give rise therefore to two
infinite series of circles, at once resembling and
differing from each other; the one takes its rise
in the centre of an infinite number of concen-
tric circles; the other has its origin in the con-
tact, at their highest points, of an infinite num-
ber of eccentric circles; the former are pro-
duced by motions which are equal and uniform;
the latter by motions which are neither uni-
form nor equal among themselves, but which
vary from one to another according to the slope.
Further, if from the two points chosen as
origins of motion, we draw lines not only along
horizontal and vertical planes but in all direc-
tions then just as in the former cases, beginning
at a single point ever-expanding circles are pro-
duced, so in the latter case an infinite number
of spheres are produced about a single point, or
rather a single sphere which expands in size
without limit: and this in two ways, one with
the origin at the centre, the other on the sur-
face of the spheres.
SALV. The idea is really beautiful and worthy
of the clever mind of Sagredo.
SIMP. As for me, I understand in a general
way how the two kinds of natural motions give
rise to the circles and spheres; and yet as to the
production of circles by accelerated motion and
its proof, I am not entirely clear; but the fact that
one can take the origin of motion either at the in-
most centre or at the very top of the sphere leads
one to think that there may be some great mys-
tery hidden in these true and wonderful results,
a mystery related to the creation of the universe
(which is said to be spherical in shape), and re-
lated also to the seat of the first cause.
SALV. I have no hesitation in agreeing with
you. But profound considerations of this kind
belong to a higher science than ours. We must
be satisfied to belong to that class of less worthy
workmen who procure from the quarry the
marble out of which, later, the gifted sculptor
produces those masterpieces which lay hidden
in this rough and shapeless exterior. Now, if
you please, let us proceed.
THEOREM VII, PROPOSITION VII
If the heights of two inclined planes are to each
other in the same ratio as the squares of their
lengths, bodies starting from rest will traverse these
planes in equal times.
THE TWO NEW SCIENCES
215
Take two planes of different lengths and dif-
ferent inclinations, AE and AB, whose heights
are AF and AD: let AF be to AD as the square
Fig. 60
of AE is to the square ofAB', then, I say, that a
body, starting from rest at A, will traverse the
planes AE and AE in equal times. From the
vertical line, draw the horizontal parallel lines
EF and DB, the latter cutting AE at G. Since
FA : DA=EA* : BA\ and since FA : DA=
EA : GA, it follows that EA : GA= EA2 : BA*.
Hence BA is a mean proportional between EA
and GA. Now since the time of descent along
AB bears to the time along AG the same ratio
which AB bears to AG and since also the time
of descent along AG is to the time along AE as
AG is to a mean proportional between AG and
AE, that is, to ABy it follows, ex aequali, that
the time along AE is to the time along AE as
AE is to itself. Therefore the times are equal.
Q. E. D.
THEOREM VIII, PROPOSITION VIII
The times of descent along all inclined planes
which intersect one and the same vertical circle,
either at its highest or lowest point, are equal to the
time of fall along the vertical diameter; for those
planes which fall short of this diameter the times
are shorter; for planes which cut this diameter, the
times are longer.
Let AB be the vertical diameter of a circle
which touches the horizontal plane. It has al-
ready been proven that the times of descent
along planes drawn from either end, A or B, to
the circumference are equal. In order to show
that the time of descent along the plane DF
which falls short of the diameter is shorter, we
may draw the plane DB which is both longer
and less steeply inclined than DF; whence it
follows that the time along DF is less than that
along DB and consequently along AB. In like
manner, it is shown that the time of descent
along CO which cuts the diameter is greater:
for it is both longer and less steeply inclined
than CB. Hence follows the theorem.
THEOREM IX, PROPOSITION IX
If from any point on a horizontal line two planes,
inclined at any angle, are drawn, and if they are
cut by a line which maizes with them angles alter-
nately equal to the angles between these planes and
the horizontal, then the times required to traverse
those portions of the plane cut off by the aforesaid
line are equal.
Through the point C on the horizontal line
X, draw two planes CD and CE inclined at any
angle whatever: at any point in the line CD lay
off the angle CDF equal to the angle XCE; let
the line DF cut CE at F so that the angles CDF
and CFD are alternately equal to XCE and
LCD; then, I say, the times of descent over CD
Fig. 61
Fig. 62
and GF are equal. Now since the angle CDF
is equal to the angle XCE by construction, it
is evident that the angle CFD must be equal
to the angle DCL. For if the common angle
DCF be subtracted from the three angles of
the triangle CDF, together equal to two right
angles, (to which are also equal all the angles
2l6
GALILEO GALILEI
which can be described about the point C on
the lower side of the line LX) there remain in
the triangle two angles, CDF and CFD, equal
to the two angles XCE and LCD; but, by hy-
pothesis, the angles CDF and XCE are equal;
hence the remaining angle CFD is equal to the
remainder DCL. Take CE equal to CD; from
the points D and E draw DA and EB perpen-
dicular to the horizontal line XL', and from the
point C draw CG perpendicular to DP. Now
since the angle CDG is equal to the angle ECB
and since DGC and CBE are right angles, it
follows that the triangles CDG and CBE are
equiangular; consequently DC : CG = CE : EB.
But DC is equal to CE, and therefore CG is
equal to EB. Since also the angles at Cand at
A, in the triangle DAC, are equal to the angles
at F and G in the triangle CGF, we have
CD : DA = FC : CG and, permutando, DC :
CF=DA : CG^DA : BE. Thus the ratio of
the heights of the equal planes CD and CE is
the same as the ratio of the lengths DC and
CF. Therefore, by Corollary I of Prop. VI,
the times of descent along these planes will be
equal. Q. E. D.
An alternative proof is the following: Draw
FS perpendicular to the horizontal line AS.
Then, since the triangle CSF is similar to the
triangle DGC, we have SF:FC=GC: CD;
and since the triangle CFG is similar to the tri-
angle DC A, we have FC : CG= CD : DA.
Hence, ex aequali, SF : CG= CG : DA. There-
fore CG is a mean proportional between SF
and DA, while DA : SF=DA2 : CG2. Again
since the triangle A CD is similar to the tri-
angle CGF, we have DA : DC= GC : CF and,
permutando, DA : CG=DC : CF: also DA2 :
CG2=DC* : CF2. But it has been shown that
DA2 : CG2=DA : SF. Therefore DC2 : CF2=
DA : FS. Hence from the above Prop. VII,
since the heights DA and FS of the planes CD
and CF are to each other as the squares of the
lengths of the planes, it follows that the times
of descent along these planes will be equal.
THEOREM X, PROPOSITION X
The times of descent along inclined planes of the
same height, but of different slope, are to each
other as the lengths of these planes; and this is true
whether the motion starts from rest or whether it
is preceded by a fall from a constant height.
Let the paths of descent be along ABC and
ABD to the horizontal plane DC so that the
falls along BD and BC are preceded by the fall
along AB; then, I say, that the time of descent
along BD is to the time of descent along J3Cas
the length BD is to BC. Draw the horizontal
line ^Fand extend DB until it cuts this line at
F; let FE be a mean proportional between DF
and F£; draw EO parallel to DC\ then AO
will be a mean proportional between CA and
AB. If now we represent the time of fall along
AB by the length AB, then the time of descent
along FB will be represented by the distance
FB-, so also the time of fall through the entire
distance AC will be represented by the mean
proportional AO : and for the entire distance
FD by FE. Hence the time of fall along the re-
mainder, BC, will be represented by BO, and
Fig. 64
that along the remainder, BD, by BE; but
since BE : BO=BD : BC, it follows, if we al-
low the bodies to fall first along AB and FB, or,
what is the same thing, along the common
stretch AB, that the times of descent along BD
and BC will be to each other as the lengths BD
and BC.
But we have previously proven that the time
of descent, from rest at B, along BD is to the
time along BC in the ratio which the length
BD bears to BC. Hence the times of descent
along different planes of constant height are to
each other as the lengths of these planes, wheth-
er the motion starts from rest or is preceded by
a fall from a constant height. Q. E. D.
THE TWO NEW SCIENCES
217
THEOREM XI, PROPOSITION XI
If a plane be divided into any two pans and if mo-
tion along it starts from rest, then the time of de-
scent along the first part is to the time of descent
along the remainder as the length of this first part
is to the excess of a mean proportional between this
first pan and the entire length over this first part.
Let the fall take place, from rest at A,
through the entire distance AB which is divid-
ed at any point C; also let AF be a mean
proportional between the entire length BA
and the first part AC; then CF will denote
the excess of the mean proportional FA
over the first part AC. Now, I say, the time
of descent along AC will be to the time of
subsequent fall through CB as the length
AC is to CF. This is evident, because the
time along AC is to the time along the en-
tire distance AB as AC is to the mean pro-
portional AF. Therefore, dividendo, the
time along AC will be to the time along the
remainder CB as AC is to CF. If we agree
65 to represent the time along AC by the
length AC then the time along CB will be rep-
resented by CF. Q. E. D.
In case the motion is not along the straight
line ACB but along the broken line ACD to the
C
B
Fig. 66
horizontal line BD, and if from F we draw the
horizontal line FE, it may in like manner be
proved that the time along AC is to the time
along the inclined line CD as AC is to CE. For
the time along AC is to the time along CB as
AC is to CF; but it has already been shown
that the time along CB, after the fall through
the distance AC, is to the time along CD, after
descent through the same distance AC, as CB
is to CD, or, as CF is to CE; therefore, ex
aequali, the time along AC will be to the time
along CD as the length AC is to the length CE.
THEOREM XII, PROPOSITION XII
If a vertical plane and any inclined plane are lim-
ited by two horizontals, and if we ta%c mean pro-
ponionals between the lengths of these planes and
those portions of them which lie between their
point of intersection and the upper horizontal,
then the time of fall along the perpendicular bears
to the time required to traverse the upper part of
the perpendicular plus the time required to traverse
the lower part of the intersecting plane the same
ratio which the entire length of the vertical bears
to a length which is the sum of the mean pro-
ponional on the vertical plus the excess of the en-
tire length of the inclined plane over its mean pro-
ponional.
Let AF and CD be two horizontal planes
limiting the vertical plane AC and the inclined
plane DF; let the two last-mentioned planes
intersect at B. Let AR be a mean proportional
between the entire vertical AC and its upper
part AB; and let FS be a mean proportional
between FD and its upper part FB. Then, I say,
the time of fall along the entire vertical path
AC bears to the time of fall along its upper
portion AB plus the time of fall along the lower
part of the inclined plane, namely, BD, the
same ratio which the length AC bears to the
mean proportional on the vertical, namely, AR,
plus the length SD which is the excess of the
entire plane DF over its mean proportional FS.
Join the points R and S giving a horizontal
line RS. Now since the time of fall through the
entire distance AC is to the time along the por-
tion AB as CA is to the mean proportional AR
it follows that, if we agree to represent the time
of fall through AC by the distance AC, the
time of fall through the distance AB will be
represented by AR; and the time of descent
through the remainder, BC, will be represented
by RC. But, if the time along AC is taken to be
equal to the length AC, then the time along
FD will be equal to the distance FD; and we
may likewise infer that the time of descent
along BD, when preceded by a fall along FB or
AB, is numerically equal to the distance DS.
2l8
GALILEO GALILEI
Therefore the time required to fall along the
path AC is equal to AR plus RC; while the time
of descent along the broken line ABD will be
equal to AR plus SD. Q. E. D.
The same thing is true if, in place of a verti-
cal plane, one takes any other plane, as for in-
stance JVO; the method of proof is also the
same.
PROBLEM I, PROPOSITION XIII
Given a perpendicular line of limited length, it is
required to find a plane having a vertical height
equal to the given perpendicular and so inclined
that a body, having fallen from rest along the
perpendicular, will ma^e its descent along the
inclined plane in the same time which it occupied
in falling through the given perpendicular.
Let AB denote the given perpendicular: pro-
long this line to C making EC equal to AB, and
draw the horizontal lines CE and AG. It is re-
quired to draw a plane from B to the horizontal
line CE such that after a body starting from
rest at A has fallen through the distance AB, it
will complete its path along this plane in an
equal time. Lay off CD equal to BC, and draw
the line BD. Construct the line BE equal to the
sum of BD and DC', then, I say, BE is the re-
quired plane. Prolong EB till it intersects the
horizontal AG at G. Let GF be a mean propor-
B
E
D
C
Fig. 68
tional between GE and GB; then EF : FZ?=
EG:GF, and^2:752==EG2:GP==EG :
GB. But EG is twice GB', hence the square of
EF is twice the square of FB', so also is the
square of DB twice the square of BC. Conse-
quently EF : FB=DB : BC, and componendo et
permutando, EB : DB+BC=*BF : BC. But EB
= DB+BC; hence BF~BC=BA. If we agree
that the length AB shall represent the time of
fall along the line AB, then GB will represent
the time of descent along GB, and GF the time
along the entire distance GE; therefore RFwill
represent the time of descent along the differ-
ence of these paths, namely, BE, after fall from
G or from A. Q. E. F.
PROBLEM II, PROPOSITION XIV
Given an inclined plane and a perpendicular pass-
ing through it, to find a length on the upper part
of the perpendicular through which a body will
fall from rest in the same time which is required
to traverse the inclined plane after fall through the
vertical distance just determined.
Let AC be the inclined plane and DB the
perpendicular. It is required to find on the ver-
tical AD a length which will be traversed by a
body, falling from rest, in the same time which
is needed by the same body to traverse the
plane AC after the aforesaid fall. Draw the hori-
zontal CB; lay off AE such that BA+2AC :
AC=AC : AE, and lay off AR such that BA :
AC= EA : AR. From R draw RX perpendicu-
lar to DB; then, I say, X is the point sought.
For since BA+2AC : AC=AC : AE, it fol-
lows, dividendo, that BA+AC : AC^CE :
AE. And since BA : AC— EA : AR, we have,
componendo, BA+AC : AC=ER : RA. But
BA + CA : AC=CE : AE, hence CE : EA=
ER : RA= sum of the antecedents: sum of the
consequents= CR : RE. Thus RE is seen to be
C B
Fig. 69
a mean proportional between CR and RA.
Moreover, since it has been assumed that BA :
AC=EA : AR, and since by similar triangles
we have BA : AC=XA : AR, it follows that
EA : AR=XA : AR. Hence EA and XA are
equal. But if we agree that the time of fall
through RA shall be represented by the length
RA, then the time of fall along RC will be rep-
resented by the length RE which is a mean pro-
portional between RA and RC\ likewise AE
will represent the time of descent along AC
after descent along RA or along AX. But the
time of fall through XA is represented by the
length XA, while RA represents the time
through RA. But it has been shown that XA
and AE arc equal. Q. E. F.
THE TWO NEW SCIENCES
219
PROBLEM III, PROPOSITION XV
Given a vertical line and a plane inclined to it, it is
required to find a length on the vertical line below
its point of intersection which will be traversed in
the same time as the inclined plane, each of these
motions having been preceded by a fall through
the given vertical line.
Let AB represent the vertical line and EC
the inclined plane; it is required to find a length
on the perpendicular below its point of inter-
section, which after a fall from A will be trav-
ersed in the same time which is needed for EC
after an identical fall from A. Draw the hori-
zontal AD, intersecting the prolongation of
CE at D\ let DE be a mean proportional be-
tween CD and DB\ lay ofTBF equal to BE\ also
let AG be a third proportional to EA and AF.
Then, I say, EG is the distance which a body,
after falling through AB, will traverse in the
A D
IG
Fig. 70
same time which is needed for the plane EC
after the same preliminary fall. For if we as-
sume that the time of fall along AE is repre-
sented by AE, then the time for DE will be
represented by DE. And since DE is a mean
proportional between BD and DC, this same
DE will represent the time of descent along the
entire distance DC while BE will represent the
time required for the difference of these paths,
namely, BC, provided in each case the fall is
from rest at D or at A. In like manner, we may
infer that BF represents the time of descent
through the distance EG after the same pre-
liminary fall; but BFis equal to BE. Hence the
problem is solved.
THEOREM XIII, PROPOSITION XVI
If a limited inclined plane and a limited vertical
line are drawn from the same point, and if the
time required for a body, starting from rest, to
traverse each of these is the same, then a body fall-
ing from any higher altitude will traverse the in-
clined plane in less time than is required for the
vertical line.
Let EB be the vertical line and CE the in-
clined plane, both starting from the common
point E, and both traversed in equal times by a
body starting from rest at E; extend the vertical
line upwards to any point A, from which falling
bodies are allowed to start. Then, I say, that
after the fall through AE, the inclined plane EC
will be traversed in less time than the perpen-
dicular EB. Join CB, draw the horizontal AD,
and prolong CE backwards until it meets the
latter in D\ let DF be a mean proportional be-
tween CD and DE while AG is made a mean
proportional between EA and AE. Draw FG
and DG\ then since the times of descent along
EC and EB, starting from rest at E, are equal, it
follows, according to Corollary II of Proposi-
A
B
Fig. 71
tion VI that the angle at C is a right angle; but
the angle at A is also a right angle and the angles
at the vertex E are equal; hence the triangles
AED and CEB are equiangular and the sides
about the equal angles are proportional; hence
BE : EC-DE : EA. Consequently the rectan-
gle BE.EA is equal to the rectangle CE.ED;
and since the rectangle CD. DE exceeds the rec-
tangle CE.ED by the square of ED, and
since the rectangle EA. AE exceeds the rectan-
gle BE.EA by the square oiEA, it follows that
220
the excess of the rectangle CD.DE over the
rectangle BA.AE, or what is the same thing,
the excess of the square of FD over the square
of AG, will be equal to the excess of the square
of DE over the square of AE, which excess is
equal to the square of AD. Therefore FZ52=
Ct?2+ZD2= GD*. Hence DF is equal to DG,
and the angle DGF is equal to the angle DFG
while the angle EGF is less than the angle EFG,
and the opposite side EF is less than the oppo-
site side EG. If now we agree to represent the
time of fall through AE by the length AE, then
the time along DE will be represented by DE.
And since AG is a mean proportional between
BA and AE, if follows that AG will represent
the time of fall through the total distance AB,
and the difference EG will represent the time
of fall, from rest at A9 through the difference of
path EB.
In like manner EF represents the time of de-
scent along EC, starting from rest at D or fall-
ing from rest at A. But it has been shown that
EF is less than EG; hence follows the theorem.
COROLLARY
From this and the preceding proposition, it
is clear that the vertical distance covered by a
freely falling body, after a preliminary fall, and
during the time-interval required to traverse an
inclined plane, is greater than the length of the
inclined plane, but less than the distance trav-
ersed on the inclined plane during an equal
time, without any preliminary fall. For since
we have just shown that bodies falling from an
elevated point A will traverse the plane EC in
Fig. 71 in a shorter time than the vertical EB, it
is evident that the distance along EB which will
be traversed during a time equal to that of de-
scent along EC will be less than the whole of
EB. But now in order to show that this vertical
GALILEO GALILEI
distance is greater than the length of the in-
clined plane EC, we reproduce Fig. 70 of the
preceding theorem in which the vertical length
BG is traversed in the same time as BC after a
preliminary fall through AB. That BG is greater
than BC is shown as follows: since BE and FB
are equal while BA is less than BD, it follows
that FB will bear to BA a greater ratio than EB
bears to BD; and, componendo, FA will bear to
BA a greater ratio than ED to DB; but FA :
AB— GF : FB (since AF is a mean proportional
between BA and AG) and in like manner ED :
BD= CE : EB. Hence GB bears to BFa greater
ratio than CB bears to BE] therefore GB is
greater than BC.
PROBLEM IV, PROPOSITION XVII
Given a vertical line and an inclined plane, it is re-
quired to lay off a distance along the given plane
which will be traversed by a body, after fall along
the perpendicular, in the same time-interval which
is needed for this body to fall from rest through the
given perpendicular.
Let AB be the vertical line and BE the in-
clined plane. The problem is to determine on
BE a distance such that a body, after falling
A D
1G
Fig. 7*
Fig- 73
through AB, will traverse it in a time equal to
that required to traverse the perpendicular AB
itself, starting from rest.
Draw the horizontal AD and extend the plane
until it meets this line in D. Lay off FB equal to
BA; and choose the point ZTsuchthatBD ; FD=
DF : DE. Then, I say, the time of descent along
BE, after fall through AB, is equal to the time
of fall, from rest at A, through AB. For, if we
assume that the length AB represents the time
of fall through AB, then the time of fall through
DB will be represented by the time DB; and
since BD : FD=DF : DE, it follows that DF
will represent the time of descent along the en-
tire plane DE while BF represents the time
through the portion BE starting from rest at D;
but the time of descent along BE after the pre-
liminary descent along DB is the same as that
THE TWO NEW SCIENCES
after a preliminary fall through AB. Hence the
time of descent along BE after AB will be BF
which of course is equal to the time of fall through
AB from rest at A. Q. E. F.
PROBLEM V, PROPOSITION XVIII
Given the distance through which a body will fall
vertically from rest during a given time-interval,
and given also a smaller time-interval, it is required
to locate another f equal} vertical distance which the
body will traverse during this given smaller time-
interval.
Let the vertical line be drawn through A, and
on this line lay off the distance AB which is
traversed by a body falling from rest at A, dur-
ing a time which may also be represented by
AB. Draw the horizontal line CBE, and on it
lay off BC to represent the given interval of
Fig- 74
time which is shorter than AB. It is required to
locate, in the perpendicular above mentioned,
a distance which is equal to AB and which will
be described in a time equal to BC. Join the
points A and C; then, since BC<BA, it follows
that the angle ZL4C<angle BCA. Construct the
angle CAE equal to BCA and let E be the point
where AE intersects the horizontal line; draw
ED at right angles to AE, cutting the vertical
at D; lay off DF equal to BA. Then, I say, that
FD is that portion of the vertical which a body
starting from rest at A will traverse during the
assigned time-interval BC. For, if in the right-
angled triangle AED a perpendicular be drawn
from the right-angle at E to the opposite side
AD, then AE will be a mean proportional be-
tween DA and AB while BE will be a mean pro-
portional between BD and BA, or between FA
and AB (seeing that FA is equal to DB); and
since it has been agreed to represent the time of
fall through AB by the distance AB% it follows
221
that AE, or EC, will represent the time of fall
through the entire distance AD, while EB will
represent the time through AF. Consequently
the remainder BC will represent the time of fall
through the remaining distance FD. Q. E. F.
PROBLEM VI, PROPOSITION XIX
Given the distance through which a body falls in a
vertical line from rest and given also the time of fall,
it is required to find the time in which the same
body will, later, traverse an equal distance chosen
anywhere in the same vertical line.
On the vertical line AB, lay off AC equal to
the distance fallen from rest at A, also locate at
random an equal distance DB. Let the time of
A
fall through AC be represented by the length
AC. It is required to find the time necessary to
traverse DB after fall from rest at A. About the
entire length AB describe the semicircle AEB;
from C draw CE perpendicular to AB; join the
points A and E; the line AE will be longer than
EC; lay off EF equal to EC. Then, I say, the dif-
ference FA will represent the time required for
fall through DB. For since AE is a mean pro-
portional between BA and AC and since AC
represents the time of fall through AC, it fol-
lows that AE will represent the time through
the entire distance AB. And since CE is a mean
proportional between DA and AC (seeing that
DA^BC) it follows that CE, that is, EF, will
represent the time of fall through AD. Hence
the difference AF will represent the time of fall
through the difference DB. Q. E. D.
COROLLARY
Hence it is inferred, that if the time of fall
from rest through any given distance is repre-
sented by that distance itself, then the time of
fall, after the given distance has been increased
222
GALILEO GALILEI
"S by a certain amount, will be represented by
the excess of the mean proportional be-
tween the increased distance and the origi-
nal distance over the mean proportional
between the original distance and the in-
crement. Thus, for instance, if we agree
that AB represents the time of fall, from
rest at A, through the distance AB, and that
AS is the increment, the time required to
traverse AB, after fall through SA, will be
B the excess of the mean proportional be-
Fig. tween SB and BA over the mean propor-
76 tional between BA and AS.
PROBLEM VII, PROPOSITION XX
Given any distance whatever and a portion of it
laid off from the point at which motion begins, it is
required to find another portion which lies at the
other end of the distance and which is traversed in
the same time as the first given portion.
Let the given distance be CB and let CD be
that part of it which is laid off from the begin-
-~ ning of motion. It is required to find another
part, at the end B, which is traversed in
the same time as the assigned portion CD.
•D Let BA be a mean proportional between
BC and CD; also let CE be a third pro-
portional to BC and CA. Then, I say, EB
will be the distance which, after fall from
C, will be traversed in the same time as CD
itself. For if we agree that CB shall repre-
sent the time through the entire distance
CB, then BA (which, of course, is a mean
A proportional between BC and CD) will
represent the time along CD; and since CA
is a mean proportional between Z?Cand CE,
it follows that CA will be the time through
p. CE; but the total length CB represents the
^' time through the total distance CB. There-
fore the difference BA will be the time along
the difference of distances, EB, after falling from
C; but this same BA was the time of fall through
CD. Consequently the distances CD and EZ?are
traversed, from rest at A, in equal times. Q. E. F.
THEOREM XIV, PROPOSITION XXI
If, on the path of a body falling vertically from
rest, one lays off a portion which is traversed in any
time you please and whose upper terminus coin-
cides with the point where the motion begins, and if
this fall is followed by a motion deflected along any
inclined plane, then the space traversed along the
inclined plane, during a time-interval equal to that
occupied in the previous vertical fall, will be greater
than twice, and less than three times, the length of
the vertical fall.
Let AB be a vertical line drawn downwards
from the horizontal line AE, and let it repre-
sent the path of a body falling from rest at A;
choose any portion AC of this path. Through C
draw any inclined plane, CG, alone which the
motion is continued after fall througn/^C. Then,
I say, that the distance traversed along this plane
CG, during the time-interval equal to that of
the fall through AC, is more than twice, but less
A E
B
Fig. 78
than three times, this same distance AC. Let us
lay off CF equal to AC, and extend the plane
GC until it meets the horizontal in E; choose G
such that CE : EF=EF : EG. If now we assume
that the time of fall along AC is represented by
the length AC, then CE will represent the time
of descent along CE, while CF, or CA, will rep-
resent the time of descent along CG. It now re-
mains to be shown that the distance CG is more
than twice, and less than three times, the dis-
tance CA itself. Since CE : EF= EF : EG, it
follows that CE : EF= CF : FG; but EC<EF,
therefore CF will be less than FG and GC will
be more than twice FC, or AC. Again since
FE<2EC (for EC is greater than CA, or CF),
we have GF less than twice FC, and also GC less
than three times CF, or CA. Q. E. D.
This proposition may be stated in a more
general form; since what has been proven for
the case of a vertical and inclined plane holds
equally well in the case of motion along a
plane of any inclination followed by motion
along any plane of less steepness, as can be seen
from the adjoining figure. The method of proof
is the same.
PROBLEM VIII, PROPOSITION XXII <
Given two unequal time- intervals, also the distance
through which a body will fall along a vertical line,
from rest, during the shorter of these intervals, it is
required to pass through the highest point of this
vertical line a plane so inclined that the time ofdc-
THE TWO NEW SCIENCES
scent along it will be equal to the longer of the given
intervals.
Let A represent the longer and B the shorter
of the two unequal time-intervals, also let CD
represent the length of the vertical fall, from
223
CE. Extend the plane at O, and lay off CF, FG
and GO equal to RN, NM, and MI respectively.
Then, I say, the time along the inclined plane
CO, after fell through AC, is equal to the time
of fall, from rest at A, through AC. For since
C
Fig- 79
rest, during the time B. It is required to pass
through the point C a plane of such a slope that
it will be traversed in the time A.
Draw from the point C to the horizontal a
line CX of such a length that B : A= CD : CX.
It is clear that CX is the plane along which a
body will descend in the given time A. For it
has been shown that the time of descent along an
inclined plane bears to the time of fall through
its vertical height the same ratio which the length
of the plane bears to its vertical height. There-
fore, the time along CX is to the time along CD
as the length CX is to the length CD, that is, as
the time-interval A is to the time-interval B:
but B is the time required to traverse the verti-
cal distance, CD, starting from rest; therefore A
is the time required for descent along the plane
CX.
PROBLEM IX, PROPOSITION XXIII
Given the time employed by a body in fatting
through a certain distance along a vertical line, it is
required to pass through the lower terminus of this
vertical fall, a plane so inclined that this body will,
after its vertical fall, traverse on this plane, during
a time-interval equal to that of the vertical fall, a
distance equal to any assigned distance, provided
this assigned distance is more than twice and less
than three times the vertical fall.
Let AS be any vertical line, and let AC de-
note both the length of the vertical fall, from
rest at A, and also the time required for this
fall. Let IR be a distance more than twice and
less than three times, AC. It is required to pass
a plane through the point C so inclined that a
body, after fall through AC, will, during the
time AC, traverse a distance equal to IR. Lay
off/Wand WM each equal to AC. Through the
point C, draw a plane CE meeting the horizon-
tal, AE, at such a point that 1M : MN=*AC :
OG : GF=FC : CE, it follows, componendo,
that OF : FG= OF : FC=FE : EC, and since
an antecedent is to its consequent as the sum of
the antecedents is to the sum of the consequents,
I M N R
we have OE : EF= EF : EC. Thus EFis a mean
proportional between OE and EC. Having
agreed to represent the time of fall through AC
by the length AC it follows that EC will repre-
sent the time along EC, and EF the time along
the entire distance EO, while the difference CF
will represent the time along the difference CO;
but CF= CA; therefore the problem is solved.
For the time CA is the time of fall, from rest at
A, through CA while CF (which is equal to CA)
is the time required to traverse CO after descent
along EC or after fall through AC. Q. E. F.
It is to be remarked also, that the same solu-
tion holds if the antecedent motion takes place,
not along a vertical, but along an inclined plane.
This case is illustrated in the following figure
where the antecedent motion is along the in-
clined plane AS underneath the horizontal AE.
The proof is identical with the preceding.
SCHOLIUM
On careful attention, it will be clear that, the
nearer the given line IR approaches to three
times the length AC, the nearer the inclined
224
GALILEO GALILEI
4L
'S
Fig. 8z
plane, CO, along which the second motion takes
place, approaches the perpendicular along which
the space traversed, during the time AC, will
be three times the distance AC. For if 1R be
taken nearly equal to three times AC, then IM
will be almost equal to MN; and since, by con-
struction, IM : MN=AG : CE, it follows that
CE is but little greater than CA: consequently
the point E will lie near the point Ay and the
lines CO and CS, forming a very acute angle,
will almost coincide. But, on the other hand, if
the given line, IR, be only the least bit longer
than twice AC, the line IM will be very short;
from which it follows that AC will be very small
in comparison with CE which is now so long
that it almost coincides with the horizontal line
drawn through C. Hence we can infer that, if,
after descent along the inclined plane AC of the
adjoining figure, the motion is continued along
a horizontal line, such as CT, the distance trav-
ersed by a body, during a time equal to the
time of fall through AC, will be exactly twice
the distance AC. The argument here employed
is the same as the preceding. For it is clear, since
OE : EF^EF : EC, that FC measures the time
of descent along CO. But, if the horizontal line
TC which is twice as long as CA, be divided in-
to two equal parts at V then this line must be
extended indefinitely in the direction of X be-
fore it will intersect the line AE produced; and
accordingly, the ratio of the infinite length TX
to the infinite length VX is the same as the ratio
of the infinite distance VX to the infinite dis-
tance CX.
The same result may be obtained by another
method of approach, namely, by returning to
the same line of argument which was employed
in the proof of the first proposition. Let us con-
sider the triangle ABC, which, by lines drawn
parallel to its base, represents for us a velocity
increasing in proportion to the time; if these
lines are infinite in number, just as the points in
the line AC are infinite or as the number of in-
stants in any interval of time is infinite, they
B
7
Z
z
z
z
z
will form the area of the triangle. Let us now
suppose that the maximum velocity attained —
that represented by the line BC — to be con-
tinued, without acceleration and at constant
value through another interval of time equal to
the first. From these velocities will be built up,
in a similar manner, the area of the parallelo-
gram ADBG, which is twice that of the triangle
ABC; accordingly, the distance traversed with
these velocities during any given interval of
time will be twice that traversed with the veloc-
ities represented by the triangle during an equal
interval of time. But along a
horizontal plane the motion is
uniform since here it experi-
ences neither acceleration nor
retardation; therefore we con-
clude that the distance CD trav-
ersed during a time-interval
equal to AC is twice the dis-
tance AC; for the latter is cov-
ered by a motion, starting
from rest and increasing in
speed in proportion to the par- Fig. 82
allel lines in the triangle, while the former is
traversed by a motion represented by the paral-
lel lines of the parallelogram which, being also
infinite in number, yield an area twice that of
the triangle.
Furthermore, we may remark that any veloc-
ity once imparted to a moving body will be rig-
idly maintained as long as the external causes of
acceleration or retardation are removed, a con-
dition which is found only on horizontal planes;
for in the case of planes which slope downwards
there is already present a cause of acceleration,
while on planes sloping upward there is retarda-
tion; from this it follows that motion along a
horizontal plane is perpetual; for, if the velocity
be uniform, it cannot be diminished or slack-
ened, much less destroyed. Further, although
any velocity which a body may have acquired
through natural fall is permanently maintained
so far as its own nature is concerned, yet it must
be remembered that if, after descent along a
plane inclined downwards, the body is deflected
to a plane inclined upward, there is already ex-
isting in this latter plane a cause of retardation;
for in any such plane this same body is subject
to a natural acceleration downwards. Accord-
ingly, we have here the superposition of two
different states, namely, the velocity acquired
during the preceding fall which if acting alone
would carry the body at a uniform rate to in-
finity, and the velocity which results from a
natural acceleration downwards common to all
THE TWO NEW SCIENCES
225
bodies. It seems altogether reasonable, there-
fore, if we wish to trace the future history of a
body which has descended along some inclined
plane and has been deflected along some plane
inclined upwards, for us to assume that the max-
imum speed acquired during descent is perma-
nently maintained during the ascent. In the
ascent, however, there supervenes a natural in-
clination downwards, namely, a motion which,
starting from rest, is accelerated at the usual
rate. If perhaps this discussion is a little obscure,
the following figure will help to make it clearer.
Let us suppose that the descent has been
made along the downward sloping plane AB,
from which the body is deflected so as to con-
tinue its motion along the upward sloping plane
BC; and first let these planes be of equal length
and placed so as to make equal angles with the
horizontal line GH. Now it is well known that
a body, starting from rest at A, and descending
along AB, acquires a speed which is proportional
C F A
B
Fig. 83
H
to the time, which is a maximum at B, and
which is maintained by the body so long as all
causes of fresh acceleration or retardation are
removed; the acceleration to which I refer is
that to which the body would be subject if its
motion were continued along the plane AB
extended, while the retardation is that which
the body would encounter if its motion were
deflected along the plane BC inclined upwards;
but, upon the horizontal plane GH, the body
would maintain a uniform velocity equal to that
which it had acquired at B after fall from A;
moreover, this velocity is such that, during an
interval of time equal to the time of descent
through AB, the body will traverse a horizontal
distance equal to twice AB. Now let us imagine
this same body to move with the same uniform
speed along the plane BC so that here also dur-
ing a time-interval equal to that of descent
along AB, it will traverse along BC extended a
distance twice AB; but let us suppose that, at
the very instant the body begins its ascent it is
subjected, by its very nature, to the same in-
fluences which surrounded it during its descent
from A along AB, namely, it descends from rest
under the same acceleration as that which was
effective in AB, and it traverses, during an equal
interval of time, the same distance along this
second plane as it did along AB; it is clear that,
by thus superposing upon the body a uniform
motion of ascent and an accelerated motion of
descent, it will be carried along the plane BC
as far as the point C where these two velocities
become equal.
If now we assume any two points D and E,
equally distant from the vertex B, we may then
infer that the descent along ED takes place in
the same time as the ascent along BE. Draw DF
parallel to BC; we know that, after descent
along AD, the body will ascend along DF; or,
if, on reaching D, the body is carried along the
horizontal DE, it will reach E with the same
momentum with which it left D; hence from E
the body will ascend as far as C, proving that
the velocity at E is the same as that at D.
From this we may logically infer that a body
which descends along any inclined plane and
continues its motion along a plane inclined up-
wards will, on account of the momentum ac-
quired, ascend to an equal height above the
horizontal; so that if the descent is along AB
the body will be carried up the plane BC as far
as the horizontal line A CD: and this is true
whether the inclinations of the planes are the
same or different, as in the case of the planes
AB and BD. But by a previous postulate the
speeds acquired by fall along variously inclined
D C A E
Fig. 84
planes having the same vertical height are the
same. If therefore, the planes EB and BD have
the same slope, the descent along EB will be
able to drive the body along BD as far as D;
and since this propulsion comes from the speed
acquired on reaching the point B, it follows
that this speed at B is the same whether the
body has made its descent along AB or EB.
Evidently, then the body will be carried up
BD whether the descent has been made along
AB or along EB. The time of ascent along BD
is however greater than that along BC, just as
the descent along EB occupies more time than
that along AB; moreover it has been demon-
strated that the ratio between the lengths of
these times is the same as that between the
lengths of the planes. We must next discover
226
GALILEO GALILEI
what ratio exists between the distances trav-
ersed in equal times along planes of different
slope, but of the same elevation, that is, along
planes which are included between the same
parallel horizontal lines. This is done as follows:
THEOREM XV, PROPOSITION XXIV
Given two parallel horizontal planes and a vertical
line connecting them; given also an inclined plane
passing through the lower extremity of this vertical
line; then, if a body fall freely along the vertical
line and have its motion reflected along the in-
dined plane, the distance which it will traverse
along this plane, during a time equal to that of the
vertical fall, is greater than once but less than twice
the vertical line.
Let fiCand HG be the two horizontal planes,
connected by the perpendicular AE; also let
EB represent the inclined plane along which
B A C
H
Fig. 85
£
the motion takes place after the body has fallen
along AEand has been reflected from E towards
B. Then, I say, that, during a time equal to that
of fall along AE, the body will ascend the in-
clined plane through a distance which is greater
than AE but less than twice AE. Lay off ED
equal to AE and choose F so that EB : BD=
BD : BF. First we shall show that F is the point
to which the moving body will be carried after
reflection from E towards B during a time equal
to that of fall along AE; and next we shall show
that the distance EF is greater than EA but less
than twice that quantity.
Let us agree to represent the time of fall along
AE by the length AE, then the time of descent
along BE, or what is the same thing, ascent
along EB will be represented by the distance EB.
Now, since DB is a mean proportional be-
tween EB and BF, and since BE is the time of
descent for the entire distance BE, it follows
that BD will be the time of descent through
BF, while the remainder DE will be the time of
descent along the remainder FE. But the time
of descent along the fall from rest at B is the
same as the time of ascent from E to F after re-
flection from E with the speed acquired during
fall either through AE or BE. Therefore, DE
represents the time occupied by the body in
passing from E to F, after fall from A to E and
after reflection along EB. But by construction
ED is equal to AE. This concludes the first part
of our demonstration.
Now since the whole of EB is to the whole of
BD as the portion DB is to the portion BF, we
have the whole of EB is to the whole of BD as
the remainder ED is to the remainder DF; but
EB>BD and hence ED>DF, and EF is less
than twice DE or AE. Q. E. D.
The same is true when the initial motion oc-
curs, not along a perpendicular, but upon an
inclined plane : the proof is also the same pro-
vided the upward sloping plane is less steep,
i.e., longer, than the downward sloping plane.
THEOREM XVI, PROPOSITION XXV
If descent along any inclined plane is followed by
motion along a horizontal plane, the time of de-
scent along the inclined plane bears to the time
required to traverse any assigned length of the hori-
zontal plane the same ratio which twice the length
of the inclined plane bears to the given horizontal
length.
Let CB be any horizontal line and AB an in-
clined plane; after descent along AB let the mo-
tion continue through the assigned horizontal
Fig. 86
distance BD. Then, I say, the time of descent
along AB bears to the time spent in traversing
BD the same ratio which twice AB bears to BD.
For, lay off BC equal to twice AB then it fol-
lows, from a previous proposition, that the time
of descent along AB is equal to the time re-
quired to traverse BC; but the time along BC is
to the time along DB as the length CB is to the
length BD. Hence the time of descent along
AB is to the time along BD as twice the dis-
tance AB is to the distance BD. Q. E. D.
PROBLEM X, PROPOSITION XXVI
Given a vertical height joining two horizontal par-
allel lines; given also a distance greater than once
and less than twice this vertical height, it is required
to pass through the foot of the given perpendicular
an inclined plane such that, after fall through the
given vertical height, a body whose motion is de-
flected along the plane will traverse the assigned
distance in a time equal to the time of vertical fall.
Let AB be the vertical distance separating
THE TWO NEW SCIENCES
227
two parallel, horizontal lines AO and BC; also
let FE be greater than once and less than twice
BA. The problem is to pass a plane through J5,
extending to the upper horizontal line, and
such that a body, after having fallen from A to
5, will, if its motion be deflected along the in-
clined plane* traverse a distance equal to EFin
a time equal to that of fall along AB. Lay off
ED equal to AB; then the remainder DF will
be less than AB since the entire length EF is
less than twice this quantity; also lay off DI
equal to DF, and choose the point X such that
El : /£>= DF : FX; from B, draw the plane BO
equal in length to EX. Then, I say, that the
plane BO is the one along which, after fall
through AB, a body will traverse the assigned
distance FE in a time equal to the time of fall
through AB. Lay off BR and RS equal to ED
and DF respectively; then since El : ID—DF :
FX, we have, componendo, ED : DI— DX :
XF= ED : DF= EX : XD= BO : OR= RO : OS.
0 A
B
D
I E
part of AC lay off CE equal to AB. Choose F
such that CA : AE= CA : CA - AB= CE : EF.
Then, I say, that FC is that distance which will,
after fall from A be traversed during a time-
X F
Fig. 87
If we represent the time of fall along AB by the
length AB, then OB will represent the time of
descent along OB, and RO will stand for the
time along OS, while the remainder BR will
represent the time required for a body starting
from rest at O to traverse the remaining dis-
tance SB. But the time of descent along SB
starting from rest at 0 is equal to the time of
ascent from B to S after fall through AB. Hence
BO is that plane, passing through B, along which
a body, after fall through AB, will traverse the
distance BS, equal to the assigned distance EF,
in the time-interval BR or BA. Q. E. F.
THEOREM XVII, PROPOSITION XXVII
If a body descends along two inclined planes of
different lengths but of the same vertical height, the
distance which it will traverse, in the lower part of
the longer plane, during a time- interval equal to
that of descent over the shorter plane, is equal to
the length of the shorter plane plus a portion of it
to which the shorter plane bears the same ratio
which the longer plane bears to the excess of the
longer over the shorter plane.
Let AC be the longer plane, AB, the shorter,
and AD the common elevation; on the lower
interval equal to that required for descent along
AB. For since CA : AE= CE : EF, it follows
that the remainder EA: the remainder AF—
CA : AE. Therefore AE is a mean proportional
between AC and AF. Accordingly, if the length
AB is employed to measure the time of fall
along AB, then the distance AC will measure
the time of descent through AC; but the time
of descent through AF is measured by the
length AE, and that through FC by EC. Now
EC= AB; and hence follows the proposition.
PROBLEM XI, PROPOSITION XXVIII
Let AG be any horizontal line touching a
circle; let AB be the diameter passing through
the point of contact; and let AE and EB repre-
sent any two chords. The problem is to deter-
mine what ratio the time of fall through AB
A G
Fig. 89
bears to the time of descent over both AE and
EB. Extend BE till it meets the tangent at G,
and draw AF so as to bisect the angle BAE.
Then, I say, the time through AB is to the sum
of the times along AE and EB as the length AE
is to the sum of the lengths AE and EF. For
since the angle FAB is equal to the angle FAE,
while the angle EAG is equal to the angle ABF
it follows that the entire angle GAP is equal to
the sum of the angles FAB and ABF. But the
228
GALILEO GALILEI
angle GFA is also equal to the sum of these two
angles. Hence the length GF is equal to the
length GA; and since the rectangle BG.GE is
equal to the square of GA, it will also be equal
to the square of GF, or BG : GF= GF : GE. If
now we agree to represent the time of descent
along AE by the length AE, then the length
GE will represent the time of descent along
GE, while GF will stand for the time of descent
through the entire distance GB; so also EF will
denote the time through EB after fall from G
or from A along AE. Consequently the time
along AE, or AB, is to the time along AE and
EB as the length AE is to AE+EF. Q. E. D.
A shorter method is to lay off GF equal to
GA, thus making GF a mean proportional be-
tween BG and GE. The rest of the proof is as
above.
THEOREM XVIII, PROPOSITION XXIX
Given a limited horizontal line, at one end of
which is erected a limited vertical line whose length
is equal to one-half the given horizontal line; then
a body, falling through this given height and hav-
ing its motion deflected into a horizontal direction,
will traverse the given horizontal distance and ver-
tical line in less time than it will any other vertical
distance plus the given horizontal distance.
B
A
N
fi
Fig. 90
Let BC be the given distance in a horizontal
plane; at the end B erect a perpendicular, on
which lay off BA equal to half BC. Then, I say,
that the time required fora body, starting from
rest at A, to traverse the two distances, AB and
BC, is the least of all possible times in which
this same distance BC together with a vertical
portion, whether greater or less than AB, can
be traversed.
Lay off EB greater than AB, as in the first
figure, and less than AB, as in the second. It
must be shown that the time required to trav-
erse the distance EB plus BC is greater than
that required for AB plus BC. Let us agree that
the length AB shall represent the time along
AB, then the time occupied in traversing the
horizontal portion BC will also be AB, seeing
that BC= 2AB; consequently the time required
for both AB and BC will be twice AB. Choose
the point O such that EB : BO^BO : BA,
then BO will represent the time of fall through
EB. Again lay off the horizontal distance BD
equal to twice BE; whence it is clear that BO
represents the time along BD after fall through
EB. Select a point N such that DB : BC^EB :
BA~ OB : BN. Now since the horizontal mo-
tion is uniform and since OB is the time occu-
pied in traversing BD, after fall from E, it fol-
lows that NB will be the time along BC after
fall through the same height EB. Hence it is
clear that OB plus BN represents the time of
traversing EB plus BC; and, since twice BA is
the time along AB plus BC, it remains to be
shown that OB+BN>2BA.
But since EB : BO=BO : BA, it follows that
EB : BA^TJB* :T£P. Moreover since EB :
BA= OB : BN it follows that OB : BN=-W5Z :
B^2. But OB : BN=(OB : BA) (BA : BN),
and therefore AB : BN= OB : BA, that is, BA
is a mean proportional between BO and BN.
Consequently OB+BN>2BA. Q. E. D.
THEOREM XIX, PROPOSITION XXX
A perpendicular is let fall from any point in a
horizontal line; it is required to pass through
any other point in this same horizontal line a
plane which shall cut the perpendicular and
along which a body will descend to the perpen-
dicular in the shortest possible time. Such a
plane will cut from the perpendicular a portion
equal to the distance of the assumed point in
the horizontal from the upper end of the per-
pendicular.
Let AC be any horizontal line and B any
point in it from which is dropped the verti-
cal line BD. Choose any point C in the hori-
zontal line and lay off, on the vertical, the dis-
tance BE equal to BC; join Cand E. Then, I say,
that of all inclined planes that can be passed
through C, cutting the perpendicular, CEis that
one along which the descent to the perpendicu-
lar is accomplished in the shortest time. For,
draw the plane CF cutting the vertical above E,
and the plane CG cutting the vertical below E;
and draw IK, a parallel vertical line, touching at
C a circle described with BCas radius. Let EK be
drawn parallel to CF, and extended to meet the
tangent, after cutting the circle at L. Now it is
clear that the time of fall along LE is equal to
the time along CE; but the time along KE is
N
A
+O
E
THE TWO NEW SCIENCES
229
greater than along LE; therefore the time along
KE is greater than along CE. But the time
along KE is equal to the time along CF, since
they have the same length and the same slope;
and, in like manner, it follows that the planes
CG and IE, having the same length and the
same slope, will be traversed in equal times.
Also, since HE<IE, the time along HE will be
less than the time along IE. Therefore, also the
time along CE (equal to the time along HE),
will be shorter than the time along IE.
Q. E. D.
THEOREM XX, PROPOSITION XXXI
If a straight line is inclined at any angle to the
horizontal and if, from any assigned point in the
horizontal, a plane of quickest descent is to be
drawn to the inclined line, that plane will be the
one which bisects the angle contained between two
lines drawn from the given point, one perpendicu-
lar to the horizontal line, the other perpendicular
to the inclined line.
Let CD be a line inclined at any angle to the
horizontal AB; and from any assigned point A
in the horizontal draw AC perpendicular to
AB, and AE perpendicular to CD; draw FA so
as to bisect the angle CAE. Then, I say, that of
all the planes which can be drawn through the
point A, cutting the line CD at any points
whatsoever AF is the one of quickest descent.
Draw FG parallel to AE; the alternate angles
GFA and FAE will be equal; also the angle
EAF is equal to the angle FAG. Therefore the
sides G-Fand GA of the triangle FGA are equal.
Accordingly, if we describe a circle about G as
B
Fig. 92
centre, with GA as radius, this circle will pass
through the point F, and will touch the hori-
zontal at the point A and the inclined line at F;
for GFC is a right angle, since GF and AE are
parallel. It is clear therefore that all lines drawn
from A to the inclined line, with the single ex-
ception of FA, will extend beyond the circum-
ference of the circle, thus requiring more time
to traverse any of them than is needed for FA.
T Q. E. D.
LEMMA
If two circles one lying within the other are in con-
tact, and if any straight line be drawn tangent to
the inner circle, cutting the outer circle, and if three
lines be drawn from the point at which the circles
are in contact to three points on the tangential
straight line, namely, the point oftangency on the
inner circle and the two points where the straight
line extended cuts the outer circle, then these three
lines will contain equal angles at the point of
contact.
Let the two circles touch each other at the
point A, the centre of the smaller being at B,
the centre of the larger at C. Draw the straight
line FG touching the inner circle at H, and cut-
ting the outer at the points F and G; also draw
the three lines AF, AH, and AG. Then, I say,
the angles contained by these lines, FAH and
GAH, are equal. Prolong AH to the circum-
ference at 7; from the centres of the circles,
draw BH and CI; join the centres B and C and
extend the line until it reaches the point of con-
tact at A and cuts the circles at the points O
and N. But now the lines BH and CI are paral-
lel, because the angles /CTVand HBO are equal,
each being twice the angle IAN. And since BH,
drawn from the centre to the point of contact
230
GALILEO GALILEI
Fig. 93
is perpendicular to FG, it follows that CI will
also be perpendicular to FG and that the arc
Fl is equal to the arc IG; consequently the
angle FAl is equal to the angle IAG. Q. E. D.
THEOREM XXI, PROPOSITION XXXII
If in a horizontal line any two points are chosen,
and if through one of these points a line be drawn in-
clined towards the other, and if from this other point
a straight line is drawn to the inclined line in such
a direction that it cuts off from the inclined line a
portion equal to the distance between the two
chosen points on the horizontal line, then the time
of descent along the line so drawn is less than
along any other straight line drawn from the same
point to the same inclined line. Along other lines
which make equal angles on opposite sides of this
line, the times of descent are the same.
Let A and B be any two points on a horizon-
tal line: through B draw an inclined straight
line EC, and from B lay off a distance BD equal
to BA; join the points A and D. Then, I say,
the time of descent along AD is less than along
any other line drawn from A to the inclined
line BC. From the point A draw AE perpendic-
ular to BA; and from the point D draw DE
perpendicular to BD, intersecting AE at E.
Since in the isosceles triangle ABD, we have
the angles BAD and EDA equal, their com-
plements DAE and EDA are equal. Hence if,
with E as centre and EA as radius, we describe
a circle it will pass through D and will touch
the lines BA and BD at the points A and D.
Now since A is the end of the vertical line AE,
the descent along AD will occupy less time
than along any other line drawn from the ex-
tremity A to the line BCand extending beyond
the circumference of the circle; which con-
cludes the first part of the proposition.
If however, we prolong the perpendicular line
AE, and choose any point F upon it, about
which as centre, we describe a circle of radius
FA, this circle AGC, will cut the tangent line
in the points G and C. Draw the lines AG and
AC which will according to the preceding lem-
ma, deviate by equal angles from the median
line AD. The time of descent along either of
these lines is the same, since they start from the
highest point A, and terminate on the circum-
ference of the circle AGC.
PROBLEM XII, PROPOSITION XXXIII
Given a limited vertical line and an inclined plane
of equal height, having a common upper ter-
minal; it is required to find a point on the vertical
line, extended upwards, from which a body will
fall and, when deflected along the inclined plane,
will traverse it in the same time-interval which is
required for fall, from rest, through the given
vertical height.
Fig. 94
Fig. 95
Let AE be the given limited vertical line
and AC an inclined plane having the same al-
titude. It is required to find on the vertical EA,
THE TWO NEW SCIENCES
extended above A, a point from which a falling
body will traverse the distance AC in the same
time which is spent in falling, from rest at A,
through the given vertical line AB. Draw the
line DCE at right angles to AC, and lay off CD
equal to AB; also join the points A and D;
then the angle ADC will be greater than the
angle CAD, since the side CA is greater than
either AB or CD. Make the angle DAE equal
to the angle ADE, and draw EF perpendicular
to AE; then EF will cut the inclined plane, ex-
tended both ways, at F. Lay off Al and AG
each equal to CF; through G draw the hori-
zontal line GH. Then, I say, H is the point
sought.
For, if we agree to let the length AB rep-
resent the time of fall along the vertical AB,
then ^Cwill likewise represent the time of de-
scent from rest at A, along AC; and since, in
the right-angled triangle AEF, the line EC has
been drawn from the right angle at E perpendic-
ular to the base AF, it follows that AE will be a
mean proportional between FA and AC, while
CE will be a mean proportional between AC
and CF, that is between CA and AL Now, since
AC represents the time of descent from A along
AC, it follows that AE will be the time along
the entire distance AF, and EC the time along
AL But since in the isosceles triangle A ED the
side EA is equal to the side ED it follows that
ED will represent the time of fall along AF,
while ZiCis the time of fall along AL Therefore
CD, that is AB, will represent the time of fall,
from rest at A, along IF; which is the same as
saying that AB is the time of fall, from G or
from H, along AC. Q. E. F.
PROBLEM XIII, PROPOSITION XXXIV
Given a limited inclined plane and a vertical line
having their highest point in common, it is re-
quired to find a point in the vertical line extended
such that a body will fall from it and then traverse
the inclined plane in the same time which is re-
quired to traverse the inclined plane alone, starting
from rest at the top of said plane.
Let AC and AB be an inclined plane and a
vertical line respectively, having a common
highest point at A. It is required to find a point
in the vertical line, above A, such that a body,
falling from it and afterwards having its motion
directed along AB, will traverse both the as-
signed part of the vertical line and the plane AB
in the same time which is required for the plane
AB alone, starting from rest at A. Draw BC a
horizontal line and lay off AN equal to AG;
choose the point L so that AB : BN— AL : LC>
Fig. 96
and lay off Al equal to AL; choose the point E
such that CE, laid off on the vertical AC pro-
duced, will be a third proportional to AC and
BL Then, I say, CE is the distance sought; so
that, if the vertical line is extended above A
and if a portion AX is laid off equal to CE, then
a body falling from X will traverse both the dis-
tances, XA and AB, in the same time as that re-
quired, when starting from A, to traverse AB
alone.
Draw XR parallel to SCand intersecting BA
produced in R; next draw ED parallel to BC
and meeting BA produced in D; on AD as
diameter describe a semicircle; from B draw BF
perpendicular to AD, and prolong it till it
meets the circumference of the circle; evidently
FB is a mean proportional between AB and BD,
while FA is a mean proportional between DA
and AB. Take BS equal to BI and FH equal to
FB. Now since AB : BD=AC : CE and since
BF is a mean proportional between AB and BD,
while BI is a mean proportional between AC
and CE, it follows that BA : AC=- FB : BS,
and since BA : AC=BA : BN=FB : BS we
shall have, convertendo, BF : F5= AB : BN= AL:
LC. Consequently the rectangle formed by FB
and CL is equal to the rectangle whose sides are
ALand SF; moreover, this rectangle AL.SF'is
the excess of the rectangle AL.FB, or ALBF,
over the rectangle ALBS, or AI.IB. But the
rectangle FB.LC is the excess of the rectangle
AC. BF over the rectangle AL.BF; and more-
over the rectangle AC.BF is equal to the rec-
tangle AB.BI since BA : AC=FB : BI\ hence
the excess of the rectangle AB . BI over the rec-
tangle ALBF, or ALFH, is equal to the ex-
cess of the rectangle ALFH over the rectangle
AL1B; therefore twice the rectangle ALFH is
equal to the sum of the rectangles AB.BI and
ALIB, or 2ALFH=2AI.IB+BP. Add ~AP to
232
each side, then
2AI.FH+AP. A
in add BF2 to each side,
2AI. FH+^+FH2. But AP= 2AHJ1F+
~AH2+TTP2\ and hence 2AI.FH+AI2 +
~FH2 = 2AH.HF + AJP + HF2. Subtracting
HF2 from each side we have 2<4/.F//+/4/2=
Since now FH is a factor
common to both rectangles, it fol-
lows that AH is equal to AI; for if
AH were either greater or smaller
than AI, then the two rectangles
AH-HF plus the square of HA
would be either larger or smaller than
the two rectangles AI.FH plus the
square of I A, a result which is con-
trary to what we have just demon-
strated.
If now we agree to represent the
time of descent along AB by the
length AB, then the time through
AC will likewise be measured by AC;
and IB, which is a mean proportional
between AC and CE, will represent
the time through CE, or XA, from
rest at X. Now, since AF is a mean
proportional between DA and AB
or between RB and AB, and since
BF, which is equal to FH, is a mean propor-
tional between AB and BD, that is between AB
and AR, it follows, from a preceding proposition
[XIX, corollary], that the difference AH repre-
sents the time of descent along AB either from
rest at R or after fall from X, while the time of
descent along AB, from rest at A, is measured by
the length AB. But as has just been shown, the
time of fall through XA is measured by IB,
while the time of descent along AB, after fall,
through RA or through XA, is IA. Therefore
the time of descent through XA plus AB is
measured by the length AB, which, of course,
also measures the time of descent, from rest at
Ay along AB alone. Q. E. F.
PROBLEM XIV, PROPOSITION XXXV
Given an inclined plane and a limited vertical
line, it is required to find a distance on the in-
clined plane which a body, starting from rest, will
traverse in the same time as that needed to traverse
both the vertical and the inclined plane.
Let AB be the vertical line and BC the in-
clined plane. It is required to lay off on BC a
distance which a body, starting from rest, will
traverse in a time equal to that which is oc-
cupied by fall through the vertical AB and by
descent of the plane. Draw the horizontal line
GALILEO GALILEI
AD, which intersects at E the prolongation of
the inclined plane CB; lay off BF equal to BA,
and about E as centre, with EF as radius de-
scribe the circle FIG. Prolong FE until it inter-
sects the circumference at G. Choose a point H
such that GB : BF=BH : HF. Draw the line
HI tangent to the circle at /. At B draw the
line BK perpendicular to FC, cutting the line
Fig. 97
EIL at L; also draw LM perpendicular to EL
and cutting BC at M. Then, I say, BM is the
distance which a body, starting from rest at B,
will traverse in the same time which is required
to descend from rest at A through both dis-
tances AB and BM. Lay off £7V equal to EL;
then since GB : BF=BH : HF, we shall have,
permutando, GB : BH= BF : HF, and, dividen-
do, GH : BH=BH : HF. Consequently the
rectangle GH.HF is equal to the square on
BH; but this same rectangle is also equal to the
square on HI; therefore BH is equal to HI.
Since, in the quadrilateral ILBH, the sides HB
and HI are equal and since the angles at B and /
are right angles, it follows that the sides BL and
LI are also equal: but EI=EF; therefore the
total length LE, or NE, is equal to the sum of
LB and EF. If we subtract the common part
EF, the remainder FN will be equal to LB:
but, by construction, FB=BA and, therefore,
LB=AB-{-BN. If again we agree to represent
the time of fall through AB by the length AB,
then the time of descent along EB will be meas-
ured by EB; moreover, since EN is a mean pro-
portional between ME and EB, it will represent
the time of descent along the whole distance
EM; therefore the difference of these distances,
BM, will be traversed, after fall from EB, or
THE TWO NEW SCIENCES
B A
233
Fig. 98
AB, in a time which is represented by BN. But
having already assumed the distance AB as a
measure of the time of fall through AB, the
time of descent along AB and BM is measured
by AB-}-BN. Since EB measures the time of
fall, from rest at E, along EB, the time from
rest at B along BM will be the mean propor-
tional between BE and BM, namely, BL. The
time therefore for the path AB+BM, starting
from rest at A is AB+BN; but the time for BM
alone, starting from rest at B, is BL; and since
it has already been shown that BL=AB-\-BN,
the proposition follows.
Another and shorter proof is the following:
Let BC be the inclined plane and BA the ver-
tical; at B draw a perpendicular to EC, extend-
ing it both ways; lay off BH equal to the excess
of BE over BA; make the angle HEL equal to
the angle BHE; prolong EL until it cuts BK in
L; at L draw LM perpendicular to EL and ex-
tend it till it meets BC in M; then, I say, BM is
the portion of BC sought. For, since the angle
MLE is a right angle, BL will be a mean pro-
portional between MB and BE, while LE is a
mean proportional between ME and BE; lay
off EN equal to LE; then NE=EL=LH, and
HB=NE-BL. But also HB=NE-(NB+BA);
therefore BN-\-BA=BL. If now we assume the
length EB as a measure of the time of descent
along EB, the time of descent, from rest at B,
along BM will be represented by BL; but, if the
descent along BM is from rest at E or at A,
then the time of descent will be measured by
BN; and AB will measure the time along AB.
Therefore the time required to traverse AB
and BM, namely, the sum of the distances AB
and BN, is equal to the time of descent, from
rest at B, along BM alone. Q. E. F.
LEMMA
Let DC be drawn perpendicular to the di-
ameter BA; from the extremity B draw the
G
Fig. 99
line BED at random; draw the line FB. Then,
I say, FB is a mean proportional between DB
and BE. Join the points E and F. Through
B, draw the tangent BG which will be paral-
lel to CD. Now, since the angle DBG is equal
to the angle FDB, and since the alternate
angle of GBD is equal to EFB, it follows that
the triangles FDB and FEB are similar and
hence BD : BF^FB : BE.
LEMMA
Let AC be a line which is longer than DF>
and let the ratio of AB to BC be greater than
that of DE to EF. Then, I say, AB is greater
A B C
E G_
Fig. 100
than DE. For, if AB bears to BC a ratio greater
than that of DE to EF, then DE will bear to
some length shorter than EF, the same ratio
which AB bears to BC. Call this length EG;
then since AB : BC= DE : EG, it follows, com-
ponendo et convertendo, that CA : AB=GD :
DE. But since CA is greater than GD, it fol-
lows that BA is greater than DE.
LEMMA
Let ACIB be the quadrant of a circle; from
B draw BE parallel to AC; about any point in
the line BE describe a circle BOES, touching
AB at B and intersecting the circumference of
the quadrant at /, Join the points C and B;
draw the line C/, prolonging it to S. Then, I
say, the line CI is always less than CO. Draw
the line AI touching the circle BOE. Then, if
the line DI be drawn, it will be equal to DB;
GALILEO GALILEI
A
\
\
Fig. 101
but, since DB touches the quadrant, Dl will I say, the time of descent along the two chords
also be tangent to it and will be at right angles DB and EC is shorter than along DC alone, or
to Al; thus Al touches the circle BOB at /. along J?C alone, starting from rest at B. Through
And since the angle AlC is greater than the M D A
angle ABC, subtending as it does a larger arc,
it follows that the angle SIN is also greater
than the angle ABC. Wherefore the arc IBS is
greater than the arc J50, and the line CS, being
nearer the centre is longer than CB. Conse-
quently CO is greater than 67, since SC : CB=
OC : CL
This result would be all the more marked if,
as in the second figure, the arc B1C were less
than a quadrant. For the perpendicular DB
would then cut the circle CIB; and so also would
Dl which is equal to BD; the angle DIA would ~.
be obtuse and therefore the line AIN would cut »—
the circle BIB. Since the angle ABC is less than
the angle AIC, which is equal to SIN, and still
less than the angle which the tangent at /
would make with the line 57, it follows that the
arc SEI is far greater than the arc BO; whence
etc. Q. E. D.
THEOREM XXII, PROPOSITION XXXVI
If from the lowest foint of a vertical circle, a chord
is drawn subtending an arc not greater than a
quadrant, and if from the two ends of this chord
two other chords be drawn to any foint on the arc,
the time of descent along the two latter chords will
be shorter than along thefirst> and shorter also, by
the same amount* than along the lower of these
two latter chords.
Let CBD be an arc, not exceeding a quad-
rant, taken from a vertical circle whose lowest
point is C; let CD be the chord subtending this
arc, and let there be two other chords drawn
from C and D to any point B on the arc. Then,
Fig. 102
the point D, draw the horizontal line MDA
cutting CB extended at A: draw DN and MC
at right angles to MD, and BN at right angles
to BD; about the right-angled triangle DBN
describe the semicircle DFBN, cutting DC at
F. Choose the point O such that DO will be a
mean proportional between CD and DF; in
like manner select Vso that AVisa mean pro-
portional between CA and AB. Let the length
PS represent the time of descent along the
whole distance DC or EC, both of which re-
quire the same time. Lay off PR such that CD :
DO^timePS. timePR. Then PR will represent
the time in which a body, starting from Z), will
traverse the distance DF, while RS will meas-
ure the time in which the remaining distance,
FC, will be traversed. But since PS is also the
time of descent, from rest at B, along BC, and if
we choose Tsuch that BC : CD=PS : PT then
PT will measure the time of descent from A to C,
THE TWO NEW SCIENCES
for we have already shown that DC is a mean
proportional between AC and CB. Finally
choose the point G such that CA : AV=PT :
PG, then PG will be the time of descent from A
to By while GT will be the residual time of de-
scent along BC following descent from A to B.
But, since the diameter, DN, of the circle
DFN is a vertical line, the chords DF and DB
will be traversed in equal times; wherefore if
one can prove that a body will traverse BG,
after descent along DB, in a shorter time than it
will PC after descent along DF he will have
proved the theorem. But a body descending
from D along DB will traverse BC in the same
time as if it had come from A along AB, seeing
that the body acquires the same momentum in
descending along DB as along AB. Hence it re-
mains only to show that descent along BC after
AB is quicker than along FC after DF. But we
have already shown that GT represents the
time along BC after AB; also that RS measures
the time along FC after DF. Accordingly it
must be shown that RS is greater than GT,
which may be done as follows : Since SP : PR=
CD : DO, it follows, invertendo et convertcndo,
that RS : SP=OC: CD', also we have SP :
PT=DC : CA. And since TP : PG= CA : AV,
it follows, invertendo, that PT : TG^AC : CV,
therefore, ex zequali, RS : GT= OC : CV. But,
is we shall presently show, OC is greater than
CV; hence the time RS is greater than the
time GT, which was to be shown. Now, since
CF is greater than CB and FD smaller than BA,
it follows that CD : DF>CA : AB. But CD :
DF=CO:OF, seeing that CD : DO=DO :
DF; and CA : AB=ZV* : VE\ Therefore CO :
OF>CV : VB, and, according to the preced-
ing lemma, CO>CV. Besides this it is clear
that the time of descent along DC is to the
time along DBG as DOC is to the sum of DO
md CV. c
SCHOLIUM
From the preceding it is possible to infer
that the path of quickest descent from one
Doint to another is not the shortest path, name-
y, a straight line, but the arc of a circle. In the
quadrant BAEC, having the side BC vertical,
iivide the arc AC into any number of equal
Darts, AD, DE, EF, FG, GC, and from C draw
straight lines to the points A, D, E, F, G; draw
dso the straight lines AD, DE, EF, FG, GG.
Evidently descent along the path ADC is
quicker than along AC alone or along DC from
*est at £). But a body, starting from rest at Ay
vill traverse DC more quickly than the path
4DC; while, if it starts from rest at A, it will
Fig. 103
traverse the path DEC in a shorter time than
DC alone. Hence descent along the three chords
ADEC, will take less time than along the two
chords ADC. Similarly, following descent along
ADE, the time required to traverse EFC is less
than that needed for EC alone*. Therefoie de-
scent is more rapid along the four chords
ADEFC than along the three ADEC. And fin-
ally a body, after descent along ADEF, will
traverse the two chords, FGC, more quickly
than FC alone. Therefore, along the five chords,
ADEFGC, descent will be more rapid than
along the four, ADEFC. Consequently the
nearer the inscribed polygon approaches a cir-
cle the shorter is the time required for descent
from A to C.
What has been proven for the quadrant holds
true also for smaller arcs; the reasoning is the
same.
PROBLEM XV, PROPOSITION XXXVII
Given a limited vertical line and an inclined plane
of equal altitude; it is required to find a distance
on the inclined plane which is equal to the vertical
line and which is traversed in an interval equal to
the time of fall along the vertical line.
Let AB be the vertical line and AC the in-
clined plane. We must locate, on the inclined
plane, a distance equal to the vertical line AB
and which will be traversed by a body starting
from rest at A in the same time needed for fall
along the vertical line. Lay off AD equal to AB,
A
Fig. 104
236
GALILEO GALILEI
and bisect the remainder DC at I. Choose the
point E such that AC : CI= CI : AE and lay off
DG equal to AE. Clearly EG is equal to AD,
and also to AB. And further, I say that EG is
that distance which will be traversed by a body,
starting from rest at A, in the same time which
is required for that body to fall through the dis-
tance AB. For since AC : CI=CI : AE=ID :
DG, we have, convertendo, CA : AI= Dl : IG.
And since the whole of CA is to the whole of A I
as the portion CI is to the portion IG, it fol-
lows that the remainder I A is to the remainder
AG as the whole of CA is to the whole of AL
Thus AI is seen to be a mean proportional
between CA and AG, while CI is a mean
proportional between CA and AE. If there-
fore, the time of fall along AB is represented
by the length AB, the time along AC will be
represented by AC, while CI, or ID, will
measure the time along AE. Since AI is a D
mean proportional between CA and AG,
and since CA is a measure of the time along
the entire distance AC, it follows that AI
is the time along AG, and the difference 1C E
is the time along the difference GC; but Dl
was the time along AE. Consequently the
lengths Dl and 1C measure the times along
AE and CG respectively. Therefore the re-
mainder DA represents the time along EG,
which of course is equal to the time along
AB. Q. E. F.
COROLLARY
From this it is clear that the distance sought
is bounded at each end by portions of the in-
clined plane which are traversed in equal times.
PROBLEM XVI, PROPOSITION XXXVIH
Given two horizontal planes cut by a vertical line,
it is required to find a point on the upper pan of
the vertical line from which bodies may fall to the
horizontal planes and there, having their motion
deflected into a horizontal direction, will, during
an interval equal to the time of fall, traverse dis-
tances which bear to each other any assigned ratio
of a smaller quantity to a larger.
Let CD and BE be the horizontal planes cut
by the vertical ACB, and let the ratio of the
smaller quantity to the larger be that of N to
FG. It is required to find in the upper part of
the vertical line, AB, a point from which a
body falling to the plane CD and there having
its motion deflected along this plane, will trav-
erse, during an interval equal to its time of fall
a distance such that if another body, falling
from this same point to the plane BE, there
have its motion deflected along this plane and
continued during an interval equal to its time
of fall, will traverse a distance which bears to the
former distance the ratio of FG to N. Lay off
GH equal to N, and select the point L so that
FH : HG= BC : CL. Then, I say, L is the point
sought. For, if we lay off CM equal to twice
CL, and draw the line LM cutting the plane
BE at O, then BO will be equal to twice BL.
And since FH : //G= BC : CL, we have, com-
ponendo et convertendo, HG : GF= N : GF=
CL : LB= CM : BO. It is clear that, since CM
is double the distance LC, the space CM is that
A
B
Fig. 105
which a body falling from L through LC will
traverse in the plane CD; and, for the same rea-
son, since BO is twice the distance BL, it is
clear that BO is the distance which a body,
after fall through LJ5, will traverse during an
interval equal to the time of its fall through LB.
Q. E. F.
SAGR. Indeed, I think we may concede to our
Academician, without flattery, his claim that in
the principle laid down in this treatise he has
established a new science dealing with a very
old subject. Observing with what ease and
clearness he deduces from a single principle the
proofs of so many theorems, I wonder not a
little how such a question escaped the attention
of Archimedes, Apollonius, Euclid and so many
other mathematicians and illustrious philoso-
phers, especially since so many ponderous tomes
have been devoted to the subject of motion.
SALV. There is a fragment of Euclid which
treats of motion, but in it there is no indication
that he ever began to investigate the property
of acceleration and the manner in which it
varies with slope. So that we may say the door
is now opened, for the first time, to a new
method fraught with numerous and wonderful
THE TWO NEW SCIENCES
results which in future years will command the
ittention of other minds.
SAGR. I really believe that just as, for in-
stance, the few properties of the circle proven
by Euclid in the Third Book of his Elements
[cad to many others more recondite, so the
principles which are set forth in this little trea-
tise will, when taken up by speculative minds,
lead to many another more remarkable result;
md it is to be believed that it will be so on ac-
:ount of the nobility of the subject, which is
superior to any other in nature.
237
During this long and laborious day, I have
enjoyed these simple theorems more than their
proofs, many of which, for their complete com-
prehension, would require more than an hour
each; this study, if you will be good enough to
leave the book in my hands, is one which I
mean to take up at my leisure after we have
read the remaining portion which deals with
the motion of projectiles; and this if agreeable
to you we shall take up tomorrow.
SALV. I shall not fail to be with you.
FOURTH DAY
SALVIATI. Once more, Simplicio is here on time;
so let us without delay take up the question of
motion. The text of our Author is as follows:
THE MOTION OF PROJECTILES
In the preceding pages we have discussed the
properties of uniform motion and of motion nat-
urally accelerated along planes of all inclina-
tions. I now propose to set forth those properties
which belong to a body whose motion is com-
pounded of two other motions, namely, one uni-
form and one naturally accelerated; these prop-
erties, well worth knowing, I propose to dem-
onstrate in a rigid manner. This is the kind of
motion seen in a moving projectile; its origin I
conceive to be as follows:
Imagine any particle projected along a hori-
zontal plane without friction; then we know,
from what has been more fully explained in the
preceding pages, that this particle will move
along this same plane with a motion which is
uniform and perpetual, provided the plane has
no limits. But if the plane is limited and ele-
vated, then the moving particle, which we im-
agine to be a heavy one, will on passing over the
edge of the plane acquire, in addition to its pre-
vious uniform and perpetual motion, a down-
ward propensity due to its own weight; so that
the resulting motion which I call projection, is
compounded of one which is uniform and hori-
zontal and of another which is vertical and nat-
urally accelerated. We now proceed to demon-
strate some of its properties, the first of which is
as follows :
THEOREM I, PROPOSITION I
A projectile which is carried by a uniform horizon-
tal motion compounded with a naturally acceler-
ated vertical motion describes a path which is a
semi- parabola.
SAGR. Here, Salviati, it will be necessary to
stop a little while for my sake and, I believe,
also for the benefit of Simplicio; for it so hap-
pens that I have not gone very far in my study
of Apollonius and am merely aware of the fact
that he treats of the parabola and other conic
sections, without an understanding of which I
hardly think one will be able to follow the proof
of other propositions depending upon them.
Since even in this first beautiful theorem the
author finds it necessary to prove that the path
of a projectile is a parabola, and since, as I im-
agine, we shall have to deal with only this kind
of curves, it will be absolutely necessary to have
a thorough acquaintance, if not with all the
properties which Apollonius has demonstrated
for these figures, at least with those which are
needed for the present treatment.
SALV. You are quite too modest, pretending
ignorance of facts which not long ago you ac-
knowledged as well known— I mean at the time
when we were discussing the strength of mate-
rials and needed to use a certain theorem of
Apollonius which gave you no trouble.
SAGR. I may have chanced to know it or may
possibly have assumed it, so long as needed, for
that discussion; but now when we have to fol-
low all these demonstrations about such curves
we ought not, as they say, to swallow it whole,
and thus waste time and energy.
SIMP. Now even though Sagredo is, as I be-
lieve, well equipped for all his needs, I do not
understand even the elementary terms; for al-
though our philosophers have treated the mo-
tion of projectiles, I do not recall their having
described the path of a projectile except to state
in a general way that it is always a curved line,
unless the projection be vertically upwards. But
if the little Euclid which I have learned since
our previous discussion does not enable me to
understand the demonstrations which are to fol-
low, then I shall be obliged to accept the the-
orems on faith without fully comprehending
them.
SALV. On the contrary, I desire that you
should understand them from the Author him-
self, who, when he allowed me to see this work
of his, was good enough to prove for me two of
the principal properties of the parabola because
I did not happen to have at hand the books of
Apollonius. These properties, which are the only
ones we shall need in the present discussion,
he proved in such a way that no prerequisite
knowledge was required. These theorems are,
338
THE TWO NEW SCIENCES
indeed, given by Apollonius, but after many
preceding ones, to follow which would take a
long while. I wish to shorten our task by deriv-
ing the first property purely and simply from
the mode of generation of the parabola, and
proving the second immediately from the first.
Beginning now with the first, imagine a right
cone, erected upon the circular base ibty with
apex at /. The section of this cone made by a
Fig. 1 06
plane drawn parallel to the side /^ is the curve
which is called a para bola. The base of this para-
bola be cuts at right angles the diameter /^ of
the circle ib\c, and the axis ad is parallel to the
side /^; now having taken any point fin the
curve bfa draw the straight \mtfe parallel to
bd; then, I say, the square of bd is to the square
otfe in the same ratio as the axis ad is to the por-
tion ae. Through the point e pass a plane parallel
to the circle ib^c, producing in the cone a circu-
lar section whose diameter is the line geh. Since
bd is at right angles to /^ in the circle ib^, the
square of bd is equal to the rectangle formed by
/Wand dkj so also in the upper circle which passes
through the points gfh the square offe is equal
to the rectangle formed by geand eh; hence the
square of Mis to the square offe as the rectangle
id'd% is to the rectangle ge*eh. And since the
line ed is parallel to hl^ the line eh, being parallel
to dl^ is equal to it; therefore the rectangle id-d1{
is to the rectangle ge>eh as id is to ge, that is, as
da is to ae\ whence also the rectangle id*dl( is to
the rectangle gc-eh, that is, the square of bd is
to the square offet as the axis da is to the por-
tion ae. Q. E. D.
The other proposition necessary for this dis-
cussion we demonstrate as follows. Let us draw
a parabola whose axis ca is prolonged upwards to
a point d\ from any point b draw the line be par-
allel to the base of the parabola; if now the point
dis chosen so that da =» ca, then, I say, the straight
line drawn through the points b and d will be
tangent to the parabola at b. For imagine, if
possible, that this line cuts the parabola above
orthatitsprolongationcuts it below,and through
any point g in it draw the straight lintfge. And
Fig. 107
since the square offe is greater than the square
of ge, the square of fe will bear a greater ratio to
the square of be than the square of ge to that of
be; and since, by the preceding proposition, the
square offe is to that of be as the line ea is to ca,
it follows that the line ea will bear to the line ca
a greater ratio than the square of ge to that of
be, or, than the square of ed to that of cd (the
sides of the triangles deg and deb being propor-
tional). But the line ea is to ea, or da, in the
same ratio as four times the rectangle ea-adis to
four times the square of ad, or, what is the same,
the square of cd, since this is four times the
square of ad; hence four times the rectangle ea •
ad bears to the square of cd a greater ratio than
the square of ed to the square of cd; but that
would make four times the rectangle ea - ad
greater than the square ofed; which is false, the
fact being just the opposite, because the two
portions ea and ad of the line ed are not equal.
Therefore the line db touches the parabola with-
out cutting it. Q. E. D.
SIMP. Your demonstration proceeds too rap-
idly and, it seems to me, you keep on assuming
that all of Euclid's theorems are as familiar and
available to me as his first axioms, which is far
from true. And now this fact which you spring
upon us, that four times the rectangle ea-ad is
240
GALILEO GALILEI
less than the square of de because the two por-
tions ea and ad of the line de are not equal brings
me little composure of mind, but rather leaves
me in suspense.
SALV. Indeed, all real mathematicians assume
on the part of the reader perfect familiarity with
at least the elements of Euclid; and here it is
necessary in your case only to recall a proposi-
tion of the Second Book in which he proves that
when a line is cut into equal and also into two
unequal parts, the rectangle formed on the un-
equal parts is less than that formed on the equal
(/. e., less than the square on half the line), by
an amount which is the square of the difference
between the equal and unequal segments. From
this it is clear that the square of the whole line
which is equal to four times the square of the
half is greater than four times the rectangle of
the unequal parts. In order to understand the
following portions of this treatise it will be nec-
essary to keep in mind the two elemental the-
orems from conic sections which we have just
demonstrated; and these two theorems are in-
deed the only ones which the Author uses. We
can now resume the text and see how he dem-
onstrates his first proposition in which he shows
that a body falling with a motion compounded
of a uniform horizontal and a naturally acceler-
ated one describes a semi-parabola.
Let us imagine an elevated horizontal line or
plane ab along which a body moves with uni-
form speed from a to b. Suppose this plane to
e d
F ^
b a
b
/*
^-7
0
S
I
n
Fig. 108
end abruptly at b; then at this point the body
will, on account of its weight, acquire also a
natural motion downwards along the perpen-
dicular bn. Draw the line be along the plane ba
to represent the flow, or measure, of time; di-
vide this line into a number of segments, be, ed,
de, representing equal intervals of time; from
the points b, c, d, e, let fall lines which are parallel
to the perpendicular bn. On the first of these
lay off any distance ci, on the second a distance
four times as long, df; on the third, one nine
times as long, eh; and so on, in proportion to the
squares of cb, db, eb, or, we may say, in the
squared ratio of these same lines. Accordingly,
we see that while the body moves from b to c
with uniform speed, it also falls perpendicularly
through the distance ci, and at the end of the
time-interval be finds itself at the point t. In like
manner at the end of the time-interval bd, which
is the double of be, the vertical fall will be four
times the first distance ci; for it has been shown
in a previous discussion that the distance trav-
ersed by a freely falling body varies as the square
of the time; in like manner the space eh trav-
ersed during the time be will be nine times ci;
thus it is evident that the distances eh, df, a will
be to one another as the squares of the lines be,
bd, be. Now from the points /', f, h draw the
straight lines io,fg, hi parallel to be; these lines
hl,fg, to are equal to eb, db and cb, respectively;
so also are the lines bo, bg, bl respectively equal
to ci, df, and eh. The square of hi is to that offg
as the line Ib is to bg; and the square offg is to
that of to as gb is to bo\ therefore the points i,f,
h, lie on one and the same parabola. In like man-
ner it may be shown that, if we take equal time-
intervals of any size whatever, and if we imagine
the particle to be carried by a similar compound
motion, the positions of this particle, at the ends
of these time-intervals, will lie on one and the
same parabola. Q. E. D.
SALV. This conclusion follows from the con-
verse of the first of the two propositions given
above. For, having drawn a parabola through
the points b and h, any other two points, /and
/, not falling on the parabola must lie either
within or without; consequently the line^/g is
either longer or shorter than the line which ter-
minates on the parabola. Therefore the square
of hi will not bear to the square offg the same
ratio as the line Ib to bg, but a greater or smaller;
the fact is, however, that the square of hi does
bear this same ratio to the square offg. Hence
the point/does lie on the parabola, and so do all
the others.
SAGR. One cannot deny that the argument is
new, subtle and conclusive, resting as it does
upon this hypothesis, namely, that the horizon-
tal motion remains uniform, that the vertical
motion continues to be accelerated downwards
in proportion to the square of the time, and that
such motions and velocities as these combine
without altering, disturbing, or hindering each
other, so that as the motion proceeds the path
of the projectile does not change into a different
curve: but this, in my opinion, is impossible.
THE TWO NEW SCIENCES
241
For the axis of the parabola along which we im-
agine the natural motion of a falling body to
take place stands perpendicular to a horizontal
surface and ends at the centre of the earth; and
since the parabola deviates more and more from
its axis no projectile can ever reach the centre of
the earth or, if it does, as seems necessary, then
the path of the projectile must transform itself
into some other curve very different from the
parabola.
SIMP. To these difficulties, I may add others.
One of these is that we suppose the horizontal
plane, which slopes neither up nor down, to be
represented by a straight line as if each point on
this line were equally distant from the centre,
which is not the case; for as one starts from the
middle and goes toward either end, he departs
farther and farther from the centre [of the earth]
and is therefore constantly going uphill, Whence
if follows that the motion cannot remain uni-
form through any distance whatever, but must
continually dimmish. Besides, I do not see how
it is possible to avoid the resistance of the medi-
um which must destroy the uniformity of the
horizontal motion and change the law of accel-
eration of falling bodies. These various difficul-
ties render it highly improbable that a result
derived from such unreliable hypotheses should
hold true in practice.
SALV. All these difficulties and objections
which you urge are so well founded that it is im-
possible to remove them; and, as for me, I am
ready to admit them all, which indeed I think
our Author would also do. I grant that these
conclusions proved in the abstract will be differ-
ent when applied in the concrete and will be
fallacious to this extent, that neither will the
horizontal motion be uniform nor the natural
acceleration be in the ratio assumed, nor the
path of the projectile a parabola, etc. But, on
the other hand, I ask you not to begrudge our
Author that which other eminent men have as-
sumed even if not strictly true. The authority
of Archimedes alone will satisfy everybody. In
his Mechanics and in his first quadrature of the
parabola he takes for granted that the beam of a
balance or steelyard is a straight line, every point
of which is equidistant from the common centre
of all heavy bodies, and that the cords by which
heavy bodies are suspended are parallel to each
other.
Some consider this assumption permissible
because, in practice, our instruments and the
distances involved are so small in comparison
with the enormous distance from the centre of
the earth that we may consider a minute of arc
on a great circle as a straight line, and may re-
gard the perpendiculars let fall from its two ex-
tremities as parallel. For if in actual practice one
had to consider such small quantities, it would
be necessary first of all to criticise the architects
who presume, by use of a plumbline, to erect
high towers with parallel sides. I may add that, in
all their discussions, Archimedes and the others
considered themselves as located at an infinite
distance from the centre of the earth, in which
case their assumptions were not false, and there-
fore their conclusions were absolutely correct.
When we wish to apply our proven conclusions
to distances which, though finite, are very large,
it is necessary for us to infer, on the basis of dem-
onstrated truth, what correction is to be made
for the fact that our distance from the centre of
the earth is not really infinite, but merely very
great in comparison with the small dimensions
of our apparatus. The largest of these will be the
range of our projectiles— and even here we need
consider only the artillery — which, however
great, will never exceed four of those miles of
which as many thousand separate us from the cen-
tre of the earth; and since these paths terminate
upon the surface of the earth only very slight
changes can take place in their parabolic figure
which, it is conceded, would be greatly altered
if they terminated at the centre of the earth.
As to the perturbation arising from the re-
sistance of the medium this is more considerable
and does not, on account of its manifold forms,
submit to fixed laws and exact description. Thus
if we consider only the resistance which the air
offers to the motions studied by us, we shall see
that it disturbs them all and disturbs them in an
infinite variety of ways corresponding to the in-
finite variety in the form, weight, and velocity
of the projectiles. For as to velocity, the greater
this is, the greater will be the resistance offered
by the air; a resistance which will be greater as
the moving bodies become less dense. So that al-
though the falling body ought to be displaced
in proportion to the square of the duration of its
motion, yet no matter how heavy the body, if
it falls from a very considerable height, the re-
sistance of the air will be such as to prevent any
increase in speed and will render the motion
uniform; and in proportion as the moving body
is less dense this uniformity will be so much the
more quickly attained and after a shorter fall.
Even horizontal motion which, if no impedi-
ment were offered, would be uniform and con-
stant is altered by the resistance of the air and
finally ceases; and here again the less dense the
body the quicker the process. Of these proper-
242
ties of weight, of velocity, and also of form, in-
finite in number, it is not possible to give any
exact description; hence, in order to handle this
matter in a scientific way, it is necessary to cut
loose from these difficulties; and having discov-
ered and demonstrated the theorems, in the case
of no resistance, to use them and apply them
with such limitations as experience will teach.
And the advantage of this method will not be
small; for the material and shape of the projec-
tile may be chosen, as dense and round as pos-
sible, so that it will encounter the least resist-
ance in the medium. Nor will the spaces and
velocities in general be so great but that we shall
be easily able to correct them with precision.
In the case of those projectiles which we use,
made of dense material and round in shape, or
of lighter material and cylindrical in shape, such
as arrows, thrown from a sling or crossbow, the
deviation from an exact parabolic path is quite
insensible. Indeed, if you will allow me a little
greater liberty, I can show you, by two experi-
ments, that the dimensions of our apparatus are
so small that these external and incidental re-
sistances, among which that of the medium is
the most considerable, are scarcely observable.
I now proceed to the consideration of motions
through the air, since it is with these that we are
now especially concerned ; the resistance of the
air exhibits itself in two ways: first by offering
greater impedance to less dense than to very
dense bodies, and secondly by offering greater
resistance to a body in rapid motion than to the
same body in slow motion.
Regarding the first of these, consider the case
of two balls having the same dimensions, but
one weighing ten or twelve times as much as the
other; one, say, of lead, the other of oak, both
allowed to fall from an elevation of 150 or 200
cubits.
Experiment shows that they will reach the
earth with slight difference in speed, showing us
that in both cases the retardation caused by the
air is small; for if both balls start at the same
moment and at the same elevation, and if the
leaden one be slightly retarded and the wooden
one greatly retarded, then the former ought to
reach the earth a considerable distance in ad-
vance of the latter, since it is ten times as heavy.
But this does not happen; indeed, the gain in
distance of one over the other does not amount
to the hundredth part of the entire fall. And in
the case of a ball of stone weighing only a third
or half as much as one of lead, the difference in
their times of reaching the earth will be scarcely
noticeable. Now since the speed acquired by a
GALILEO GALILEI
leaden ball in falling from a height of 200 cubits
is so great that if the motion remained uniform
the ball would, in an interval of time equal to
that of the fall, traverse 400 cubits, and since
this speed is so considerable in comparison with
those which, by use of bows or other machines
except fire arms, we are able to give to our pro-
jectiles, it follows that we may, without sensible
error, regard as absolutely true those proposi-
tions which we are about to prove without con-
sidering the resistance of the medium.
Passing now to the second case, where we have
to show that the resistance of the air for a rapid-
ly moving body is not very much greater than
for one moving slowly, ample proof is given by
the following experiment. Attach to two threads
of equal length — say four or five yards— two
equal leaden balls and suspend them from the
ceiling; now pull them aside from the perpen-
dicular, the one through 80 or more degrees,
the other through not more than four or five
degrees; so that, when set free, the one falls,
passes through the perpendicular, and describes
large but slowly decreasing arcs of 160, 150, 140
degrees, etc, ; the other swinging through small
and also slowly diminishing arcs of 10, 8, 6, de-
grees, etc.
In the first place it must be remarked that one
pendulum passes through its arcs of 180°, 160°,
etc., in the same time that the other swings
through its 10°, 8°, etc., from which it follows
that the speed of the first ball is 16 and 18 times
greater than that of the second. Accordingly, if
the air offers more resistance to the high speed
than to the low, the frequency of vibration in
the large arcs of 180° or 160°, etc., ought to be
less than in the small arcs of 10°, 8°, 4°, etc., and
even less than in arcs of 2°, or i°; but this pre-
diction is not verified by experiment; because if
two persons start to count the vibrations, the
one the large, the other the small, they will dis-
cover that after counting tens and even hun-
dreds they will not differ by a single vibration,
not even by a fraction of one.
This observation justifies the two following
propositions, namely, that vibrations of very
large and very small amplitude all occupy the
same time and that the resistance of the air does
not affect motions of high speed more than those
of low speed, contrary to the opinion hitherto
generally entertained.
SAGR. On the contrary, since we cannot deny
that the air hinders both of these motions, both
becoming slower and finally vanishing, we have
to admit that the retardation occurs in the same
proportion in each case. But how ? How, indeed,
THE TWO NEW SCIENCES
243
could the resistance offered to the one body be
greater than that offered to the other except by
the impartation of more momentum and speed
to the fast body than to the slow? And if this is
so the speed with which a body moves is at once
the cause and measure of the resistance which it
meets. Therefore, all motions, fast or slow, are
hindered and diminished in the same propor-
tion; a result, it seems to me, of no small im-
portance.
SALV. We are able, therefore, in this second
case tosay that theerrors, neglecting those which
are accidental, in the results which we are about
to demonstrate are small in the case of our ma-
chines where the velocities employed are mostly
very great and the distances negligible in com-
parison with the semidiameter of the earth or
one of its great circles.
SIMP. I would like to hear your reason for
putting the projectiles of fire arms, /. e., those
using powder, in a different class from the pro-
jectiles employed in bows, slings, and crossbows,
on the ground of their not being equally subject
to change and resistance from the air.
SALV. I am led to this view by the excessive
and, so to speak, supernatural violence with
which such projectiles are launched; for, indeed,
it appears to me that without exaggeration one
might say that the speed of a ball fired either
from a musket or from a piece of ordnance is
supernatural. For if such a ball be allowed to fall
from some great elevation its speed will, owing
to the resistance of the air, not go on increasing
indefinitely; that which happens to bodies of
small density in falling through short distances
— I mean the reduction of their motion to uni-
formity— will also happen to a ball of iron or
lead after it has fallen a few thousand cubits;
this terminal or final speed is the maximum
which such a heavy body can naturally acquire
in falling through the air. This speed I estimate
to be much smaller than that impressed upon
the ball by the burning powder.
An appropriate experiment will serve to dem-
onstrate this fact. From a height of one hundred
or more cubits fire a gun loaded with a lead bul-
let, vertically downwards upon a stone pave-
ment; with the same gun shoot against a similar
stone from a distance of one or two cubits, and
observe which of the two balls is the more flat-
tened. Now if the ball which has come from the
greater elevation is found to be the less flattened
of the two, this will show that the air has hin-
dered and diminished the speed initially impart-
ed to the bullet by the powder, and that the air
will not permit a bullet to acquire so great a
speed, no matter from what height it falls; for if
the speed impressed upon the ball by the fire
does not exceed that acquired by it in falling
freely then its downward blow ought to be
greater rather than less.
This experiment I have not performed, but I
am of the opinion that a musket- ball or cannon-
shot, falling from a height as great as you please,
will not deliver so strong a blow as it would if
fired into a wall only a few cubits distant, i. e., at
such a short range that the splitting or rending
of the air will not be sufficient to rob the shot of
that excess of supernatural violence given it by
the powder.
The enormous momentum of these violent
shots may cause some deformation of the tra-
jectory, making the beginning of the parabola
flatter and less curved than the end; but, so far
as our Author is concerned, this is a matter of
small consequence in practical operations, the
main one of which is the preparation of a table
of ranges for shots of high elevation, giving the
distance attained by the ball as a function of the
angle of elevation; and since shots of this kind
are fired from mortars using small charges and
imparting no supernatural momentum they fol-
low their prescribed paths very exactly.
But now let us proceed with the discussion in
which the Author invites us to the study and
investigation of the motion of a body when that
motion is compounded of two others; and first
the case in which the two are uniform, the one
horizontal, the other vertical.
THEOREM II, PROPOSITION II
When the motion of a body is the resultant of two
uniform motions, one horizontal, the other perpen-
dicular, the square of the resultant momentum is
equal to the sum of the squares of the two com-
ponent momenta.
Let us imagine any body urged by two uni-
form motions and let ab represent the vertical
displacement, while be represents the displace-
Fig. 109
ment which, in the same interval of time, takes
place in a horizontal direction. If then the dis-
tances ab and be are traversed, during the same
time-interval, with uniform motions the corre-
sponding momenta will be to each other as the
distances ab and be are to each other; but the
body which is urged by these two motions de-
244
scribes the diagonal ac; its momentum is propor-
tional to ac. Also the square of ac is equal to the
sum of the squares of ab and be. Hence the square
of the resultant momentum is equal to the sum
of the squares of the two momenta ab and be.
Q. E. D.
SIMP. At this point there is just one slight
difficulty which needs to be cleared up; for it
seems to me that the conclusion just reached
contradicts a previous proposition in which it is
claimed that the speed of a body coming from a
to b is equal to that in coming from a to c; while
now you conclude that the speed at c is greater
than that at b.
SALV. Both propositions, Simplicio, are true,
yet there is a great difference between them.
Here we are speaking of a body urged by a single
motion which is the resultant of two uniform
motions, while there we were speaking of two
bodies each urged with naturally accelerated
motions, one along the vertical ab the other along
the inclined plane ac. Besides the time-intervals
were there not supposed to be equal, that along
the incline ac being greater than that along the
vertical ab; but the motions of which we now
speak, those along ab, be, ac, are uniform and
simultaneous.
SIMP. Pardon me; I am satisfied; pray go on.
SALV. Our Author next undertakes to explain
what happens when a body is urged by a motion
compounded of one which is horizontal and uni-
form and of another which is vertical but natu-
rally accelerated; from these two components
results the path of a projectile, which is a para-
bola. The problem is to determine the speed of
the projectile at each point. With this purpose
in view our Author sets forth as follows the man-
ner, or rather the method, of measuring such
speed along the path which is taken by a heavy
body starting from rest and falling with a natu-
rally accelerated motion.
THEOREM III, PROPOSITION III
Let the motion take place along the line ab,
starting from rest at a, and in this line choose
any point c. Let ac represent the time, or the
measure of the time, required for the body to
fall through the space ac; let ac also represent
the velocity at c acquired by a fall through the
distance ac. In the line ab select any other point
b. The problem now is to determine the velocity
at b acquired by a body in falling through the
distance ab and to express this in terms of the
velocity at c, the measure of which is the length
ac. Take as a mean proportional between ac and
ab. We shall prove that the velocity at b is to
GALILEO GALILEI
that at c as the length as is to the length ac. Draw
the horizontal line cd, having twice the length
of ac, and be, having twice the length of ba. It
then follows, from the preceding theorems, that
-a
Fig. no
a body falling through the distance ac, and turned
so as to move along the horizontal cd with a uni-
form speed equal to that acquired on reaching c
will traverse the distance cdin the same interval
of time as that required to fall with accelerated
motion from a to c. Likewise be will be traversed
in the same time as ba. But the time of descent
through ab is as; hence the horizontal distance
be is also traversed in the time as. Take a point
/such that the time as is to the time ac as be is to
bl; since the motion along be is uniform, the dis-
tance bl, if traversed with the speed acquired at
b, will occupy the time ac; but in this same time-
interval, ac, the distance cd is traversed with
the speed acquired in c. Now two speeds are to
each other as the distances traversed in equal
intervals of time. Hence the speed at c is to the
speed at b as cd is to bl. But since dc is to be as
their halves, namely, as ca is to ba, and since be
is to bl as ba is to sa; it follows that dc is to bl as
ca is to sa. In other words, the speed at c is to
that at b as ca is to sa, that is, as the time of fall
through ab.
The method of measuring the speed of a body
along the direction of its fall is thus clear; the
speed is assumed to increase directly as the time.
But before we proceed further, since this dis-
cussion is to deal with the motion compounded
of a uniform horizontal one and one accelerated
vertically downwards — the path of a projectile,
namely, a parabola — it is necessary that we de-
fine some common standard by which we may
estimate the velocity, or momentum of both
motions; and since from the innumerable uni-
form velocities one only, and that not selected
at random, is to be compounded with a velocity
acquired by naturally accelerated motion, I can
think of no simpler way of selecting and meas-
uring this than to assume another of the same
kind.1 For the sake of clearness, draw the verti-
1 Galileo here proposes to employ as a standard of vel-
ocity the terminal speed of a body falling freely from a
given height. TRANS.
THE TWO NEW SCIENCES
245
cal line ac to meet the horizontal line be. Ac is
the height and be the amplitude of the semi-
parabola ab, which is the resultant of the two
motions, one that of a body falling from rest at
a, through the distance ac> with naturally ac-
Fig. in
celerated motion, the other a uniform motion
along the horizontal ad. The speed acquired at
c by a fall through the distance ac is determined
by the height ac; for the speed of a body falling
from the same elevation is always one and the
same; but along the horizontal one may give a
body an infinite number of uniform speeds.
However, in order that I may select one out of
this multitude and separate it from the rest in a
perfectly definite manner, I will extend the
height ca upwards to e just as far as is necessary
and will call this distance ae the "sublimity."
Imagine a body to fall from rest at e; it is clear
that we may make its terminal speed at a the
same as that with which the same body travels
along the horizontal line ad; this speed will be
such that, in the time of descent along ea, it will
describe a horizontal distance twice the length
of ca. This preliminary remark seems necessary.
The reader is reminded that above I have
called the horizontal line cb the "amplitude" of
the semi-parabola ab; the axis ac of this parab-
ola, I have called its "altitude*1; but the line ea
the fall along which determines the horizontal
speed I have called the "sublimity." These mat-
ters having been explained, I proceed with the
demonstration.
SAGR. Allow me, please, to interrupt in order
that I may point out the beautiful agreement
between this thought of the Author and the
views of Plato concerning the origin of the
various uniform speeds with which the heaven-
ly bodies revolve. The latter chanced upon the
idea that a body could not pass from rest to any
given speed and maintain it uniformly except
by passing through all the degrees of speed in-
termediate between the given speed and rest.
Plato thought that God, after having created
the heavenly bodies, assigned them the proper
and uniform speeds with which they were for-
ever to revolve; and that He made them start
from rest and move over definite distances un-
der a natural and rectilinear acceleration such
as governs the motion of terrestrial bodies. He
added that once these bodies had gained their
proper and permanent speed, their rectilinear
motion was converted into a circular one, the
only motion capable of maintaining uniform-
ity, a motion in which the body revolves with-
out either receding from or approaching its de-
sired goal. This conception is truly worthy of
Plato; and it is to be all the more highly prized
since its underlying principles remained hidden
until discovered by our Author who removed
from them the mask and poetical dress and set
forth the idea in correct historical perspective.
In view of the fact that astronomical science
furnishes us such complete information con-
cerning the size of the planetary orbits, the dis-
tances of these bodies from their centres of
revolution, and their velocities, I cannot help
thinking that our Author (to whom this idea of
Plato was not unknown) had some curiosity to
discover whether or not a definite "sublimity"
might be assigned to each planet, such that, if
it were to start from rest at this particular height
and to fall with naturally accelerated motion
along a straight line, and were later to change
the speed thus acquired into uniform motion,
the size of its orbit and its period of revolution
would be those actually observed.
SALV. I think I remember his having told me
that he once made the computation and found
a satisfactory correspondence with observa-
tion. But he did not wish to speak of it, lest in
view of the odium which his many new discov-
eries had already brought upon him, this
might be adding fuel to the fire. But if any one
desires such information he can obtain it for
himself from the theory set forth in the present
treatment.
We now proceed with the matter in hand,
which is to prove:
PROBLEM I, PROPOSITION IV
To determine the momentum of a projectile at
each particular point in its given parabolic path.
Let bee be the semi-parabola whose ampli-
tude is cd and whose height is db> which latter
246
GALILEO GALILEI
extended upwards cuts the tangent of the para-
bola ca in a . Through the vertex draw the hori-
zontal line bi parallel to cd. Now if the ampli-
tude cd is equal to the entire height da, then bi
will be equal to ba and also to bd; and if we
take ab as the measure of the time required for
fall through the distance ab and also of the mo-
mentum acquired at b in consequence of its fall
from rest at a, then if we turn into a horizontal
direction the momentum acquired by fall
through ab, the space traversed in the same in-
terval of time will be represented by dc which
is twice bi. But a body which falls from rest at b
along the line bd will during the same time-in-
terval fall through the height of the parabola
bd. Hence a body falling from rest at a, turned
into a horizontal direction with the speed ab,
will traverse a space equal to dc. Now if one su-
perposes upon this motion a fall along bd, trav-
ersing the height bd while the parabola be is
described, then the momentum of the body at
112
the terminal point c is the resultant of a uni-
form horizontal momentum, whose value is
represented by ab, and of another momentum
acquired by fall from b to the terminal point
d or c; these two momenta are equal. If, there-
fore, we take ab to be the measure of one of
these momenta, say, the uniform horizontal
one, then bi, which is equal to bd, will rep-
resent the momentum acquired at d or c; and
ia will represent the resultant of these two
momenta, that is, the total momentum with
which the projectile, travelling along the para-
bola, strikes at c.
With this in mind let us take any point on
the parabola, say e, and determine the momen-
tum with which the projectile passes that point.
Draw the horizontal efand take bg a mean pro-
portional between bd and bf. Now since ab, or
bd, is assumed to be the measure of the time and
of the momentum acquired by falling from rest
at b through the distance bd, it follows that bg
will measure the time and also the momentum
acquired at/ by fall from b. If therefore we lay
off bo, equal to bg, the diagonal line joining a
and o will represent the momentum at the point
e; because the length ab has been assumed to
represent the momentum at b which, after di-
version into a horizontal direction, remains con-
stant; and because bo measures the momentum
at/or <?, acquired by fall, from rest at b, through
the height bf. But the square of ao equals the
sum of the squares of ab and bo. Hence the the-
orem sought.
SAGR. The manner in which you compound
these different momenta to obtain their result-
ant strikes me as so novel that my mind is left
in no small confusion. I do not refer to the com-
position of two uniform motions, even when un-
equal, and when one takes place along a hori-
zontal, the other along a vertical direction; be-
cause in this case 1 am thoroughly convinced
that the resultant is a motion whose square is
equal to the sum of the squares of the two com-
ponents. The confusion arises when one under-
takes to compound a uniform horizontal mo-
tion with a vertical one which is naturally ac-
celerated. I trust, therefore, we may pursue this
discussion more at length.
SIMP. And I need this even more than you
since I am not yet as clear in my mind as I ought
to be concerning those fundamental propositions
upon which the others rest. Even in the case of
the two uniform motions, one horizontal, the
other perpendicular, I wish to understand bet-
ter the manner in which you obtain the result-
ant from the components. Now, Salviati, you
understand what we need and what we desire.
SALV. Your request is altogether reasonable
and I will see whether my long consideration of
these matters will enable me to make them clear
to you. But you must excuse me if in the ex-
planation I repeat many things already said by
the Author.
Concerning motions and their velocities or
momenta whether uniform or naturally acceler-
ated, one cannot speak definitely until he has
established a measure for such velocities and also
for time. As for time we have the already widely
adopted hours, first minutes and second min-
utes. So for velocities, just as for intervals of
time, there is need of a common standard which
shall be understood and accepted by everyone,
and which shall be the same for all. As has al-
ready been stated, the Author considers the ve-
locity of a freely falling body adapted to this
purpose, since this velocity increases according
to the same law in all parts of the world ; thus
THE TWO NEW SCIENCES
247
for instance the speed acquired by a leaden ball
of a pound weight starting from rest and falling
vertically through the height of, say, a spear's
length is the same in all places; it is therefore ex-
cellently adapted for representing the momen-
tum acquired in the case of natural fall.
It still remains for us to discover a method of
measuring momentum in the case of uniform
motion in such a way that all who discuss the
subject will form the same conception of its size
and velocity. This will prevent one person from
imagining it larger, another smaller, than it
really is; so that in the composition of a given
uniform motion with one which is accelerated
different men may not obtain different values
for the resultant. In order to determine and rep-
resent such a momentum and particular speed
our Author has found no better method than to
use the momentum acquired by a body in nat-
urally accelerated motion. The speed of a body
which has in this manner acquired any momen-
tum whatever will, when converted into uni-
form motion, retain precisely such a speed as,
during a time-interval equal to that of the fall,
will carry the body through a distance equal to
twice that of the fall. But since this matter is
one which is fundamental in our discussion it is
well that we make it perfectly clear by means of
some particular example.
Let us consider the speed and momentum ac-
quired by a body falling through the height, say,
of a spear as a standard which we may use in the
measurement of other speeds and momenta as
occasion demands; assume for instance that the
time of such a fall is four seconds; now in order
to measure the speed acquired from a fall through
any other height, whether greater or less, one
must not conclude that these speeds bear to one
another the same ratio as the heights of fall; for
instance, it is not true that a fall through four
times a given height confers a speed four times
as great as that acquired by descent through the
given height; because the speed of a naturally
accelerated motion does not vary in proportion
to the time. As has been shown above, the ratio
of the spaces is equal to the square of the ratio of
the times.
If, then, as is often done for the sake of brev-
ity, we take the same limited straight line as the
measure of the speed, and of the time, and also
of the space traversed during that time, it fol-
lows that the duration of fall and the speed ac-
quired by the same body in passing over any
other distance, is not represented by this second
distance, but by a mean proportional between
the two distances. This I can better illustrate by
d
Lc
Fig.
"3
an example. In the vertical line ac^ lay off the
portion ab to represent the distance traversed
by a body falling freely with accelerated
motion: the time of fall may be represent-
ed by any limited straight line, but for
the sake of brevity, we shall represent it
by the same length ab; this length may
also be employed as a measure of the mo-
mentum and speed acquired during the
motion; in short, let ab be a measure of
the various physical quantities which
enter this discussion.
Having agreed arbitrarily upon ab as a
measure of these three different quanti-
ties, namely, space, time, and momen-
tum, our next task is to find the time re-
quired for fall through a given vertical
distance ac, also the momentum acquired at
the terminal point r, both of which are to be
expressed in terms of the time and momentum
represented by ab. These two required quan-
tities are obtained by laying off a d> a mean pro-
portional between ab and ac; in other words, the
time of fall from a to c is represented by ad on
the same scale on which we agreed that the time
of fall from a to b should be represented by ab.
In like manner, we may say that the momen-
tum acquired at c is related to that acquired at
by in the same manner that the line ad is related
to ab, since the velocity varies directly as the
time, a conclusion, which although employed as
a postulate in Proposition III, is here amplified
by the Author.
This point being clear and well-established
we pass to the consideration of the momentum
in the case of two compound motions, one of
which is compounded of a uniform horizontal
and a uniform vertical motion, while the other
is compounded of a uniform horizontal and a
naturally accelerated vertical motion. If both
components are uniform, and one at right angles
to the other, we have already seen that the square
of the resultant is obtained by adding the squares
of the components [p. 244], as will be clear from
the following illustration.
Fig. 114
Let us imagine a body to move along the ver-
tical ab with a uniform momentum of 3, and on
248
GALILEO GALILEI
reaching b to move toward c with a momentum
of 4, so that during the same time-interval it will
traverse 3 cubits along the vertical and 4 along
the horizontal. But a particle which moves with
the resultant velocity will, in the same time,
traverse the diagonal ac, whose length is not 7
cubits— -the sum of ab (3) and be (4) — but 5,
which is inpotenza equal to the sum of 3 and 4,
that is, the squares of 3 and 4 when added make
25, which is the square of ac, and is equal to the
sum of the squares of ab and be. Hence ac is rep-
resented by the side —or we may say the root —
of a square whose area is 25, namely 5.
As a fixed and certain rule for obtaining the
momentum which results from two uniform
momenta, one vertical, the other horizontal, we
have therefore the following: take the square of
each, add these together, and extract the square
root of the sum, which will be the momentum
resulting from the two. Thus, in the above ex-
ample, the body which in virtue of its vertical
motion would strike the horizontal plane with a
momentum of 3, would, owing to its horizontal
motion alone, strike at c with a momentum of 4 ;
but if the body strikes with a momentum which
is the resultant of these two, its blow will be
that of a body moving with a momentum of 5;
and such a blow will be the same at all points of
the diagonal ac, since its components are always
the same and never increase or diminish.
Let us now pass to the consideration of a uni-
form horizontal motion compounded with the
vertical motion of a freely falling body starting
from rest. It is at once clear that the diagonal
. which represents the motion compounded of
these two is not a straight line, but, as has been
demonstrated, a semi-parabola, in which the
momentum is always increasing because the
speed of the vertical component is always increas-
ing. Wherefore, to determine the momentum at
any given point in the parabolic diagonal, it is
necessary first to fix upon the uniform horizon-
tal momentum and then, treating the body as
one falling freely, to find the vertical momen-
tum at the given point; this latter can be deter-
mined only by taking into account the duration
of fall, a consideration which does not enter into
the composition of two uniform motions where
the velocities and momenta are always the same;
but here where one of the component motions
has an initial value of zero and increases its speed
in direct proportion to the time, it follows that
the time must determine the speed at the as-
signed point. It only remains to obtain the mo-
mentum resulting from these two components
(as in the case of uniform motions) by placing
the square of the resultant equal to the sum of
the squares of the two components. But here
again it is better to illustrate by means of an
example.
On the vertical aclay off any portion ab which
we shall employ as a measure of the space trav-
ersed by a body falling freely along the perpen-
dicular, likewise as a measure of the time and
also of the speed or, we may say, of the momenta.
It is at once clear that if the momentum of a
body at b, after having fallen from rest at a, be
Fig. 115
diverted along the horizontal direction bd, with
uniform motion, its speed will be such that, dur-
ing the time-interval ab, it will traverse a dis-
tance which is represented by the line bd and
which is twice as great as ab. Now choose a point
c, such that be shall be equal to ab, and through c
draw the line re equal and parallel tobd; through
the points b and e draw the parabola bei. And
since, during the time-interval ab, the horizon-
tal distance bd or ce, double the length ab, is
traversed with the momentum ab, and since
during an equal time-interval the vertical dis-
tance be is traversed, the body acquiring at c a
momentum represented by the same horizontal,
bd, it follows that during the time ab the body
will pass from b to e along the parabola be, and
will reach e with a momentum compounded of
two momenta each equal to ab. And since one
of these is horizontal and the other vertical, the
square of the resultant momentum is equal to
the sum of the squares of these two components,
/'. e., equal to twice either one of them.
Therefore, if we lay off the distance bf, equal
to ba, and draw the diagonal af, it follows that
the momentum at e will exceed that of a body
at b after having fallen from a, or what is the
THE TWO NEW SCIENCES
249
same thing, will exceed the horizontal momen-
tum along bd, in the ratio ofafto ab.
Suppose now we choose for the height of fall
a distance bo which is not equal to but greater
than ab, and suppose that bg represents a mean
proportional between ba and bo; then, still re-
taining ba as a measure of the distance fallen
through, from rest at a, to £, also as a measure of
the time and of the momentum which the fall-
ing body acquires at b, it follows that bg will be
the measure of the time and also of the momen-
tum which the body acquires in falling from b
to o. Likewise just as the momentum ab during
the time ab carried the body a distance along
the horizontal equal to twice ab, so now, during
the time-interval bg, the body will be carried
in a horizontal direction through a distance
which is greater in the ratio of bg to ba. Lay
off Ib equal to bg and draw the diagonal a\
from which we have a quantity compounded
of two velocities, one horizontal, the other ver-
tical; these determine the parabola. The hori-
zontal and uniform velocity is that acquired at
b in falling from a ; the other is that acquired at
0, or, we may say, at /', by a body falling through
the distance bo, during a time measured by the
line bg, which line bg also represents the mo-
mentum of the body. And in like manner we
may, by taking a mean proportional between
the two heights, determine the momentum at
the extreme end of the parabola where the
height is less than the sublimity ab; this mean
proportional is to be drawn along the horizontal
in place of bf, and also another diagonal in place
of af, which diagonal will represent the mo-
mentum at the extreme end of the parabola.
To what has hitherto been said concerning
the momenta, blows or shocks of projectiles, we
must add another very important considera-
tion; to determine the force and energy of the
shock it is not sufficient to consider only the
speed of the projectiles, but we must also take
into account the nature and condition of the
target which, in no small degree, determines the
efficiency of the blow. First of all, it is well
known that the target suffers violence from the
speed of the projectile in proportion as it partly
or entirely stops the motion; because if the
blow falls upon an object which yields to the
impulse without resistance such a blow will be
of no effect; likewise, when one attacks his en-
emy with a spear and overtakes him at an in-
stant when he is fleeing with equal speed, there
will be no blow but merely a harmless touch.
But if the shock falls upon an object which
yields only in part then the blow will not have
its full effect, but the damage will be in propor-
tion to the excess of the speed of the projectile
over that of the receding body; thus, for exam-
ple, if the shot reaches the target with a speed
of 10 while the latter recedes with a speed of 4,
the momentum and shock will be represented
by 6. Finally the blow will be a maximum, in so
far as the projectile is concerned, when the tar-
get does not recede at all but if possible com-
pletely resists and stops the motion of the pro-
jectile. I have said in so far as the projectile is
concerned because if the target should approach
the projectile the shock of collision would be
greater in proportion as the sum of the two
speeds is greater than that of the projectile
alone.
Moreover it is to be observed that the amount
of yielding in the target depends not only upon
the quality of the material, as regards hard-
ness, whether it be of iron, lead, wool, etc., but
also upon its position. If the position is such
that the shot strikes it at right angles, the mo-
mentum imparted by the blow will be a maxi-
mum; but if the motion be oblique, that is to
say slanting, the blow will be weaker; and more
and more so in proportion to the obliquity ; for,
no matter how hard the material of the target
thus situated, the entire momentum of the shot
will not be spent and stopped; the projectile
will slide by and will, to some extent, continue
its motion along the surface of the opposing
body.
All that has been said above concerning the
amount of momentum in the projectile at the
extremity of the parabola must be understood
to refer to a blow received on a line at right
angles to this parabola or along the tangent to
the parabola at the given point; for, even though
the motion has two components, one horizon-
tal, the other vertical, neither will the mo-
mentum along the horizontal nor that upon
a plane perpendicular to the horizontal be a
maximum, since each of these will be received
obliquely.
SAGR. Your having mentioned these blows
and shocks recalls to my mind a problem, or
rather a question, in mechanics of which no
author has given a solution or said anything
which diminishes my astonishment or even
partly relieves my mind.
My difficulty and surprise consist in not
being able to see whence and upon what prin-
ciple is derived the energy and immense force
which makes its appearance in a blow; for in-
stance, we see the simple blow of a hammer,
weighing not more than 8 or 10 Ibs., overcom-
250
ing resistances which, without a blow, would
not yield to the weight of a body producing im-
petus by pressure alone, even though that body
weighed many hundreds of pounds. I would like
to discover a method of measuring the force of
such a percussion. I can hardly think it infinite,
but incline rather to the view that it has its
limit and can be counterbalanced and measured
by other forces, such as weights, or by levers or
screws or other mechanical instruments which
are used to multiply forces in a manner which
I satisfactorily understand.
SALV. You are not alone in your surprise at
this effect or in obscurity as to the cause of this
remarkable property. I studied this matter my-
self for a while in vain; but my confusion mere-
ly increased until finally meeting our Academi-
cian I received from him great consolation.
First he told me that he also had for a long time
been groping in the dark; but later he said that,
after having spent some thousands of hours in
speculating and contemplating thereon, he had
arrived at some notions which are far removed
from our earlier ideas and which are remarkable
for their novelty. And since now I know that
you would gladly hear what these novel ideas
are I shall not wait for you to ask but promise
that, as soon as our discussion of projectiles is
completed, I will explain all these fantasies, or
if you please, vagaries, as far as I can recall them
from the words of our Academician. In the
meantime we proceed with the propositions of
the author.
PROPOSITION V, PROBLEM
Having given a parabola, find the point, in its
axis extended upwards, from which a particle
must fall in order to describe this same parabola.
GALILEO GALILEI
in order that, after the momentum which it ac-
quires at a has been diverted into a horizontal
direction, it will describe the parabola ab. Draw
the horizontal ag, parallel to bh, and having
laid off fl/*equal to ah, draw the straight line bf
which will be a tangent to the parabola at £,
and will intersect the horizontal ag at g: choose
e such that ag will be a mean proportional be-
tween a/and ae. Now I say that e is the point
above sought. That is, if a body falls from rest
at this point e, and if the momentum acquired
at the point a be diverted into a horizontal
direction, and compounded with the momen-
tum acquired at h in falling from rest at a, then
the body will describe the parabola ab. For if
we understand ea to be the measure of the time
of fall from e to a, and also of the momentum
acquired at a, then ag (which is a mean pro-
portional between ea and of) will represent the
time and momentum of fall from/to a or, what
is the same thing, from a to h; and since a body
falling from e, during the time ea, will, owing
to the momentum acquired at a, traverse at
uniform speed a horizontal distance which is
twice ea, it follows that, the body will if im-
pelled by the same momentum, during the
time-interval ag traverse a distance equal to
twice ag which is the half of bh. This is true be-
cause, in the case of uniform motion, the spaces
traversed vary directly as the times. And like-
wise if the motion be vertical and start from
rest, the body will describe the distance ah in
the time ag. Hence the amplitude bh and the
altitude ah are traversed by a body in the same
time. Therefore the parabola ab will be de-
scribed by a body falling from the sublimity of e.
Q. E. F.
Fig. 116
M
Let ab be the given parabola, hb its ampli-
tude, and he its axis extended. The problem is
to find the point e from which a body must fall
COROLLARY
Hence it follows that half the base, or ampli-
tude, of the semi-parabola (which is one-quar-
ter of the entire amplitude) is a mean propor-
tional between its altitude and the sublimity
from which a falling body will describe this
same parabola.
PROPOSITION VI, PROBLEM
Given the sublimity and the altitude of a parabola,
to find its amplitude.
Let the line ac, in which lie the given alti-
tude cb and sublimity ab, be perpendicular to
the horizontal line cd. The problem is to find
the amplitude, along the horizontal cd, of the
semi-parabola which is described with the sub-
limity ba and altitude be. Lay off cd equal to
twice the mean proportional between cb and
THE TWO NEW SCIENCES
251
Fig. 117
ba. Then cd will be the amplitude sought, as is
evident from the preceding proposition.
THEOREM. PROPOSITION VII
If projectiles describe semi-parabolas of the same
amplitude, the momentum required to describe
that one whose amplitude is double its altitude is
less than that required for any other.
Let bd be a semi-parabola whose amplitude
cd is double its altitude cb; on its axis extended
upwards lay off ba equal to its altitude be. Draw
the line ad which will be a tangent to the para-
bola at d and will cut the horizontal line be at
the point £, making be equal to be and also to
ba. It is evident that this parabola will be de-
scribed by a projectile whose uniform horizon-
tal momentum is that which it would acquire
at b in falling from rest at a and whose naturally
accelerated vertical momentum is that of the
body falling to c, from rest at b. From this it
follows that the momentum at the terminal
point d, compounded of these two, is repre-
sented by the diagonal ae, whose square is equal
to the sum of the squares of the two compo-
nents. Now let gd be any other parabola what-
ever having the same amplitude cd, but whose
altitude eg is either greater or less than the al-
titude be. Let hd be the tangent cutting the
horizontal through g at ^. Select a point / such
that hg:g^g^:gl. Then from a preceding
proposition [V], it follows that gl will be the
height from which a body must fall in order to
describe the parabola gd.
Let gm be a mean proportional between ab
and gl; then gm will [Prop. IV] represent the
time and momentum acquired at g by a fall
from /; for ab has been assumed as a measure of
both time and momentum. Again let gn be a
mean proportional between be and eg; it will
then represent the time and momentum which
the body acquires at c in falling from g. If now
we join m and n, this line mn will represent the
momentum at do( the projectile traversing the
parabola dg; which momentum is, I say, greater
that that of the projectile travelling along the
parabola bd whose measure was given by ae.
For since gn has been taken as a mean propor-
tional between be and ge; and since be is equal
to be and also to !(g (each of them being the half
of de) it follows that eg:gn — gn :g^ and as r^or
(hg) is to g^so is flg2 tog^2: but by construction
hg'.gk^g^gl- Hence !vgz :g%? = g{: gl. But g{:
gl=gf?:gm2, since gm is a mean proportional
between J(g and gl. Therefore the three squares
n&> fy>* mS f°rrn a continued proportion, gn2:
^2__^2.— 2 Ancj the sum of the two extremes
which is equal to the square of mn is greater
252
GALILEO GALILEI
than twice the square of ^; but the square of
ae is double the square of g\. Hence the square
of mn is greater than the square of ae and the
length mn is greater than the length ae.
~ Q. E. D.
COROLLARY
Conversely, it is evident that less momentum
will be required to send a projectile from the
terminal point d along the parabola bd than
along any other parabola having an elevation
greater or less than that of the parabola bd, for
which the tangent at d makes an angle of 45°
with the horizontal. From which it follows that
if projectiles are fired from the terminal point
d, all having the same speed, but each having a
different elevation, the maximum range, i.e.,
amplitude of the semi-parabola or of the entire
parabola, will be obtained when the elevation is
45°: the other shots, fired at angles greater or
less will have a shorter range.
SAGR. The force of rigid demonstrations such
as occur only in mathematics fills me with won-
der and delight. From accounts given by gun-
ners, I was already aware of the fact that in the
use of cannon and mortars, the maximum range,
that is the one in which the shot goes farthest,
is obtained when the elevation is 45° or, as they
say, at the sixth point of the quadrant; but to
understand why this happens far outweighs the
mere information obtained by the testimony of
others or even by repeated experiment.
SALV. What you say is very true. The knowl-
edge of a single fact acquired through a dis-
covery of its causes prepares the mind to under-
stand and ascertain other facts without need of
recourse to experiment, precisely as in the pres-
ent case, where by argumentation alone the
Author proves with certainty that the maxi-
mum range occurs when the elevation is 45°.
He thus demonstrates what has perhaps never
been observed in experience, namely, that of
other shots those which exceed or fall short of
45° by equal amounts have equal ranges; so that
if the balls have been fired one at an elevation
of 7 points, the other at 5, they will strike the
level at the same distance: the same is true if
the shots are fired at 8 and at 4 points, at 9 and
at 3, etc. Now let us hear the demonstration of
THEOREM. PROPOSITION VIII
The amplitudes of two parabolas described by
projectiles fired with the same speed, but at angles
of elevation which exceed and fall short of 45° by
equal amounts, are equal to each other.
In the triangle mcb let the horizontal side be
and the vertical cm, which form a right angle at
c, be equal to each other; then the angle mbc
will be a semi- right angle; let the line cm be
prolonged to d, such a point that the two angles
at b, namely mbe and mbd, one above and the
Fig. 119
other below the diagonal mb, shall be equal. It
is now to be proved that in the case of two para-
bolas described by two projectiles fired from b
with the same speed, one at the angle of ebc, the
other at the angle of dbc, their amplitudes will
be equal. Now since the external angle bmc is
equal to the sum of the internal angles mdb and
dbm we may also equate to them the angle
mbc; but if we replace the angle dbm by mbe,
then this same angle mbc is equal to the two
mbe and bdc: and if we subtract from each side
of this equation the angle mbe, we have the re-
mainder bdc equal to the remainder ebc. Hence
the two triangles deb and bee are similar. Bisect
the straight lines dc and ec in the points h and/ :
and draw the lines hiandfg parallel to the hori-
zontal cb, and choose /such that dh:hi—ih:hl.
Then the triangle ihl will be similar to ihd, and
also to the triangle egf; and since jiAand £/are
equal, each being half of be, it follows that hi
is equal tofe and also tofc; and if we add to
each of these the common part fh, it will be
seen that ch is equal to//.
Let us now imagine a parabola described
through the points h and b whose altitude is he
and sublimity hi. Its amplitude will be cb which
is double the length hi since hi is a mean pro-
portional between dh (or ch) and hi. The line
db is tangent to the parabola at b, since ch is
equal to hd. If again we imagine a parabola de-
scribed through the points/and b, with a sub-
limity // and altitude fc, of which the mean
proportional is^, or one-half of cb, then, as be-
fore, will cb be the amplitude and the line eb a
tangent at b; for ef and fc are equal. But the
two angles dbc and ebc, the angles of elevation,
differ by equal amounts from a 45° angle.
Hence follows the proposition.
THE TWO NEW SCIENCES
THEOREM. PROPOSITION IX
The amplitudes of two parabolas are equal when
their altitudes and sublimities are inversely pro-
portional.
Let the altitude g/"of the parabola^X bear to
the altitude cb of the parabola bd the same
ratio which the sublimity ba bears to the sub-
limity^?; then, I say, the amplitude hgis equal
to the amplitude dc. For since the first of these
quantities, gf, bears to the second, cb, the same
ratio which the third, ba, bears to the fourth,/*?,
it follows that the area of the rectangle gf-fe is
equal to that of the rectangle cb-ba; therefore
Fig. 120
squares which are equal to these rectangles are
equal to each other. But [by Proposition VI]
the square of half of gh is equal to the rectangle
gf*fe; and the square of half of cd is equal to the
rectangle cb-ba. Therefore these squares and
their sides and the doubles of their sides are
equal. But these last are the amplitudes gh and
cd. Hence follows the proposition.
LEMMA FOR THE FOLLOWING PROPOSITION
If a straight line be cut at any point whatever and
mean proportionals between this line and each of
its parts be ta^en, the sum of the squares of these
mean proportionals is equal to the square of the
entire line.
Let the line ab be cut at c. Then, I say, that
the square of the mean proportional between
Fig. 121
ab and ac plus the square of the mean propor-
tional between ab and cb is equal to the square
of the whole line ab. This is evident as soon as
we describe a semicircle upon the entire line
ab, erect a perpendicular cd at c, and draw da
and db. For da is a mean proportional between
ab and 0c while db is a mean proportional be-
tween ab and be: and since the angle adb, in-
scribed in a semicircle, is*a right angle the sum
of the squares of the lines da and db is equal to
the square of the entire line ab. Hence follows
the proposition.
THEOREM. PROPOSITION X
The momentum acquired by a panicle at the ter-
minal point of any semi-parabola is equal to that
which it would acquire in falling through a verti-
cal distance equal to the sum of the sub-
limity and the altitude of the semi-
parabola.
Let ab be a semi-parabola having a
sublimity da and an altitude ac, the
sum of which is the perpendicular^.
Now, I say, the momentum of the par-
ticle at b is the same as that which it
would acquire in falling freely from d
to c. Let us take the length of dc itself
as a measure of time and momentum,
and lay off cf equal to the mean pro-
portional between cd and da; also lay
off ce a mean proportional
between cd and ca. Now cf
is the measure of the time
and of the momentum ac-
quired by fall, from rest at
d, through the distance da;
while ce is the time and
momentum of fall, from
rest at a, through the dis-
tance ca; also the diagonal
ef will represent a momen-
tum which is the resultant
of these two, and is there-
fore the momentum at the
terminal point of the pa-
rabola, b.
Fig. 122
And since dc has been cut at some point a
and since <r/*and ce are mean proportionals be-
tween the whole of cd and its parts, da and ac,
it follows, from the preceding lemma, that the
sum of the squares of these mean proportionals
is equal to the square of the whole: but the
square of ef is also equal to the sum of these
same squares; whence it follows that the line ef
is equal to dc.
Accordingly, the momentum acquired at c
by a particle in falling from d is the same as that
acquired at b by a particle traversing the para-
bola ab. Q. E. D.
254
GALILEO GALILEI
COROLLARY
Hence it follows that, in the case of all para-
bolas where the sum of the sublimity and alti-
tude is a constant, the momentum at the ter-
minal point is a constant.
PROBLEM. PROPOSITION XI
Given the amplitude and the speed at the terminal
point of a semi-parabola, to find its altitude.
Let the given speed be represented by the
vertical line ab, and the amplitude by the hori-
zontal line be; it is required to find the sublim-
ity of the semi-parabola whose terminal speed
is ab and amplitude be. From what precedes
[Cor. Prop. V] it is clear that half the amplitude
be is a mean proportional between the altitude
Fig. 123
and sublimity of the parabola of which the ter-
minal speed is equal, in accordance with the
preceding proposition, to the speed acquired
by a body in falling from rest at a through the
distance ab. Therefore the line ba must be cut
at a point such that the rectangle formed by its
two parts will be equal to the square of half be,
namely bd. Necessarily, therefore, bd must not
exceed the half of ba; for of all the rectangles
formed by parts of a straight line the one of
greatest area is obtained when the line is divid-
ed into two equal parts. Let e be the middle
point of the line ab; and now if bd be equal to
be the problem is solved; for be will be the alti-
tude and ea the sublimity of the parabola. (In-
cidentally, we may observe a consequence al-
ready demonstrated, namely: of all parabolas
described with any given terminal speed that
for which the elevation is 45° will have the
maximum amplitude.)
But suppose that bd is less than half of ba,
which is to be divided in such a way that the
rectangle upon its parts may be equal to the
square of bd. Upon ea as diameter describe a
semicircle efa, in which draw the chord of,
equal to bd: join fe and lay off the distance eg
equal to^. Then the rectangle bg-ga plus the
square of eg will be equal to the square of ea,
and hence also to the sum of the squares of af
andfe. If now we subtract the equal squares of
fe and ge there remains the rectangle bg-ga
equal to the square of af, that is, of bd, a line
which is a mean proportional between bg and
ga; from which it is evident that the semi-para-
bola whose amplitude is be and whose terminal
speed is represented by ba has an altitude bg
and a sublimity ga.
If however we lay off hi equal to ga, then bi
will be the altitude of the semi-parabola ic, and
ia will be its sublimity. From the preceding
demonstration we are able to solve the follow-
ing problem.
PROBLEM. PROPOSITION XII
To compute and tabulate the amplitudes of all
semi-parabolas which are described by projectiles
fired with the same initial speed.
From the foregoing it follows that, whenever
the sum of the altitude and sublimity is a con-
Fig. 124
stant vertical height for any set of parabolas,
these parabolas are described by projectiles
having the same initial speed; all vertical
THE TWO NEW SCIENCES
255
heights thus obtained are therefore included
between two parallel horizontal lines. Let cb
represent a horizontal line and ab a vertical line
of equal length; draw the diagonal ac; the angle
acb will be one of 45°; let d be the middle point
of the vertical line ab. Then the semi-parabola
dc is the one which is determined by the sub-
limity ad and the altitude db, while its terminal
speed at c is that which would be acquired at b
by a particle falling from rest at a. If now ag be
drawn parallel to be, the sum of the altitude
and sublimity for any other semi-parabola hav-
ing the same terminal speed will, in the manner
explained, be equal to the distance between the
parallel lines ag and be. Moreover, since it has
already been shown that the amplitudes of two
semi-parabolas are the same when their angles
of elevation differ from 45° by like amounts, it
follows that the same computation which is em-
ployed for the larger elevation will serve also
for the smaller. Let us also assume 10000 as the
greatest amplitude for a parabola whose angle of
elevation is 45°; this then will be the length of
the line ba and the amplitude of the semi-para-
bola be. This number, 10000, is selected be-
cause in these calculations we employ a table of
tangents in which this is the value of the tan-
gent of 45°. And now, coming down to busi-
ness, draw the straight line ce making an acute
angle ecb greater than acb: the problem now is
to draw the semi-parabola to which the line ec
is a tangent and for which the sum of the sub-
limity and the altitude is the distance ba. Take
the length of the tangent be from the table of
tangents, using the angle bee as an argument:
let/ be the middle point of be; next find a third
proportional to bfand bi (the half of be) which
is of necessity greater than fa. Call this/?. We
have now discovered that, for the parabola in-
scribed in the triangle ecb having the tangent
ce and the amplitude cb, the altitude is bfand
the sublimity fo. But the total length of bo ex-
ceeds the distance between the parallels ag and
cb, while our problem was to keep it equal to
this distance : for both the parabola sought and
the parabola dc are described by projectiles
fired from c with the same speed. Now since an
infinite number of greater and smaller parabo-
las, similar to each other, may be described
within the angle bee we must find another
parabola which like cd has for the sum of its
altitude and sublimity the height ba, equal
to be.
Therefore lay off cr so that, ob:ba = bc:cr;
then cr will be the amplitude of a semi-parabola
for which bee is the angle of elevation and for
which the sum of the altitude and sublimity is
the distance between the parallels ga and cb, as
desired. The process is therefore as follows: One
draws the tangent of the given angle bee; takes
half of this tangent, and adds to it the quantity,
fo, which is a third proportional to the half of
this tangent and the half of be; the desired am-
plitude cr is then found from the following
proportion ob:ba = bc:cr. For example, let the
angle ecb be one of 50°; its tangent is 1 1918, half
of which, namely bf, is 5959; half of be is 5000;
the third proportional of these halves is 4195,
which added to bf gives the value 10154 for bo.
Further, as ob is to ab, that is, as 10154 *s to
10000, so is be, or 10000 (each being the tan-
gent of 45°) to cr, which is the amplitude sought
and which has the value 9848, the maximum
amplitude being be, or 10000. The amplitudes
of the entire parabolas are double these, name-
ly, 19696 and 20000. This is also the amplitude
of a parabola whose angle of elevation is 40°,
since it deviates by an equal amount from one
of 45°.
SAGR. In order to thoroughly understand
this demonstration I need to be shown how the
third proportional of bfand bi is, as the Author
indicates, necessarily greater than fa.
SALV. This result can, I think, be obtained as
follows. The square of the mean proportional
between two lines is equal to the rectangle
formed by these two lines. Therefore the square
of bi (or of bd which is equal to bi) must be
equal to the rectangle formed by fb and the
desired third proportional. This third propor-
tional is necessarily greater than fa because the
rectangle formed by bfand fa is less than the
square of bd by an amount equal to the square
of df, as shown in Euclid, n. i. Besides it is to
be observed that the point/, which is the mid-
dle point of the tangent eb, falls in general
above a and only once at a; in which cases it is
self-evident that the third proportional to the
half of the tangent and to the sublimity bi lies
wholly above a. But the Author has taken a
case where it is not evident that the third pro-
portional is always greater than fa, so that when
laid off above the point fit extends beyond the
parallel ag.
Now let us proceed. It will be worth while,
by the use of this table, to compute another
giving the altitudes of these semi-parabolas de-
scribed by projectiles having the same initial
speed. The construction is as follows:
described with the same in-
itial speed.
49
5<>
5'
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
Angle of
Elevation
44"
43
42
41
40
39
38
37
36
35
34
33
32
3°
29
28
27
26
25
24
23
22
21
Angle of
Elevation
GALILEO GALILEI
Altitudes of semi-parabolas stood to remain constant. Next we must find
and determine the altitude, which we shall ac-
complish by so dividing oh that the rectangle
contained by its parts shall be equal to the
square of half the amplitude, be. Let /denote
this point of division and d and / be the middle
points of ob and be respectively. The square of
ib is equal to the rectangle bf-fo; but the square
of do is equal to the sum of the rectangle bf-fo
and the square of//. If, therefore, from the
square of do we subtract the square of bi which
is equal to the rectangle bf'fo, there will remain
the square of//. The altitude in question, bf, is
now obtained by adding to this length,//, the
line bd. The process is then as follows: From the
square of half of bo which is
known, subtract the square
of bi which is also known;
take the square root of the
remainder and add to it the
known length db; then you
have the required altitude,
2
3
4
6
7
8
9
10
ii
12
3
13
28
50
76
1 08
150
194
245
3°2
365
432
506
585
670
760
855
955
1060
1170
1285
1402
1527
1685
1786
1922
2061
2204
235 i
2499
2653
2810
2967
3128
3289
3456
3621
3793
3962
4132
4302
4477
4654
4827
5000
Angle of
Elevation
46°
47
48
49
50
52
53
54
55
56
57
58
59
60
61
62
63
64
256
Amplitudes of semi-
parabolas described
with the same ini-
tial speed.
Angle of
Elevation
45° 10000
46 9994
47 9976
48 9945
9902
9848
9782
9704
9612
9511
9396
9272
9136
8989
8829 31 15
8659 30 i 6
8481 29 17
8290 28 i 8
8090 27 19
7880 26 20
7660 25 21
7431 24 22
7191
6944 22 24
6692 21 25
6428 20 26
6157 19 27
5878 18 28
5592 17 29
5300 i 6 30
5000 15 31
4694 14 32
4383 ^3 33
4067 12 34
3746 ii 35
3420 10 36
3090 9 37
2756 8 38
24'9 7 39
2079 6 40
1736 5 4i
1391 4 42 4477 87 9972
i°44 3 43 4654 88 9987
698 2 44 4827 89 9998
349 i 45 5000 90 10000
PROBLEM. PROPOSITION XIII
From the amplitudes of semi-parabolas given in
the preceding table to find the altitudes of each of
the parabolas described with the same initial
speed.
Let be denote the given amplitude; and let
ob, the sum of the altitude and sublimity, be
the measure of the initial speed which is under-
66
67
68
69
70
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
5346
5523
5698
5868
6038
6207
6379
6546
6710
6873
7^33
7190
7348
7502
7649
7796
7939
8078
8214
8346
8474
8597
8715
8830
8940
9045
9144
9240
9330
Example. To find the alti-
tude of a semi-parabola de-
scribed with an angle of ele-
vation of 55°. From the pre-
ceding table the amplitude
\°
f
d
C /
b
Fig. 125
9493
9567
9636
9698
9755
9806
9851
9890
9924
is seen to be 9396, of which the half is 4698, and
the square 22071204. When this is subtracted
from the square of the half of bo, which is al-
ways 25,000,000, the remainder is 2928796, of
which the square root is approximately 1710.
Adding this to the half of bo, namely 5000, we
have 6710 for the altitude of bf.
It will be worth while to add a third table
giving the altitudes and sublimities for para-
bolas in which the amplitude is a constant.
SAGR. I shall be very glad to see this; for from
it I shall learn the difference of speed and force
required to fire projectiles over the same range
with what we call mortar shots. This difference
will, I believe, vary greatly with the elevation
so that if, for example, one wished to employ an
elevation of 3° or 4°, or 87° or 88° and yet give
the ball the same range which it had with an
elevation of 45° (where we have shown the ini-
tial speed to be a minimum) the excess offeree
required will, I think, be very great.
SALV. You are quite right, sir; and you will
find that in order to perform this operation
completely, at all angles of elevation, you will
have to make great strides toward an infinite
speed. We pass now to the consideration of the
table.
THE TWO NEW SCIENCES
257
Table giving the altitudes and sublimities of
parabolas of constant amplitude, namely
10000, computed for each degree of eleva-
tion.
Angle of Alti-
Angle of Alti-
Elevatton tude
Sublimity
Elevation tude Sublimity
1°
87
286533
46°
5*77
4828
2
175
142450
47
5363
4662
3
262
95802
48
5553
4502
4
349
7I53I
49
5752
4345
5
437
57M2
50
5959
4196
6
525
47573
51
6174
4048
7
614
40716
52
6399
3906
8
702
35587
53
6635
3765
9
792
3r565
54
6882
3632
10
881
28367
55
7141
35°°
ii
972
25720
56
7413
3372
12
1063
235*8
57
7699
3247
13
1154
21701
58
8002
3*23
1246
20056
59
8332
3004
15
*339
18663
60
8600
2887
16
H34
17405
61
9020
2771
17
1529
16355
62
9403
2658
18
1624
63
9813
2547
19
1722
14522
64
10251
2438
20
1820
13736
65
10722
2331
21
1919
13024
66
11230
2226
22
2020
12376
67
11779
2122
23
2123
11778
68
12375
2020
2226
11230
69
13025
1919
25
2332
10722
70
13237
1819
26
2439
10253
71
14521
1721
27
2547
9814
72
15388
1624
28
2658
9404
73
1528
29
2772
9020
74
*7437
*433
3°
2887
8659
75
18660
*339
3i
3O()8
8336
76
20054
1246
32
3I24
8001
77
21657
**54
33
3247
7699
78
23523
1062
34
3373
7413
79
25723
972
35
7141
80
28356
881
36
3633
6882
81
3*569
792
37
3768
6635
82
35577
702
38
3906
6395
83
40222
613
39
4049
6174
84
47572
525
40
4196
5959
85
57150
437
4346
5752
86
349
42
4502
5553
87
954°5
262
43
4662
5362
88
143181
*74
44
4828
5*77
89
286499
87
45
5000
5000
90
infinita
PROPOSITION XIV
To find for each degree of elevation the altitudes
and sublimities of parabolas of constant ampli-
tude.
The problem is easily solved. For if we as-
sume a constant amplitude of 10000, then half
the tangent at any angle of elevation will be the
altitude. Thus, to illustrate, a parabola having
an angle of elevation of 30° and an amplitude
of 10000, will have an altitude of 2887, which
is approximately one-half the tangent. And
now the altitude having been found, the sub-
limity is derived as follows. Since it has been
proved that half the amplitude of a semi-para-
bola is the mean proportional between the al-
titude and sublimity, and since the altitude has
already been found, and since the semi-ampli-
tude is a constant, namely 5000, it follows that
if we divide the square of the semi-amplitude
by the altitude we shall obtain the sublimity
sought. Thus in our example the altitude was
found to be 2887: the square of 5000 is 25,000,-
ooo which divided by 2887 gives the approxi-
mate value of the sublimity, namely 8659.
SALV. Here we see, first of all, how very true
is the statement made above, that, for different
angles of elevation, the greater the deviation
from the mean, whether above or below, the
greater the initial speed required to carry the
projectile over the same range. For since the
speed is the resultant of two motions, namely,
one horizontal and uniform, the other vertical
and naturally accelerated; and since the sum
of the altitude and sublimity represents this
speed, it is seen from the preceding table that
this sum is a minimum for an elevation of 45°
where the altitude and sublimity are equal,
namely, each 5000; and their sum 10000. But if
we choose a greater elevation, say 50°, we shall
find the altitude 5959, and the sublimity 4196,
giving a sum of 10155; in like manner we shall
find that this is precisely the value of the speed
at 40° elevation, both angles deviating equally
from the mean.
Secondly, it is to be noted that, while equal
speeds are required for each of two elevations
that are equidistant from the mean, there is
this curious alternation, namely, that the alti-
tude and sublimity at the greater elevation cor-
respond inversely to the sublimity and altitude
at the lower elevation. Thus in the preceding
example, an elevation of 50° gives an altitude
of 5959 and a sublimity of 4196; while an ele-
vation of 40° corresponds to an altitude of 4196
and a sublimity of 5959. And this holds true in
general; but it is to be remembered that, in
order to escape tedious calculations, no account
has been taken of fractions which are of little
moment in comparison with such large num-
bers.
SAGR. I note also in regard to the two compo-
nents of the initial speed that the higher the
258
GALILEO GALILEI
shot the less is the horizontal and the greater
the vertical component; on the other hand, at
lower elevations where the shot reaches only a
small height the horizontal component of the
initial speed must be great. In the case of a pro-
jectile fired at an elevation of 90°, I quite un-
derstand that all the force in the world would
not be sufficient to make it deviate a single fin-
ger's breadth from the perpendicular and that
it would necessarily fall back into its initial pos-
ition; but, in the case of zero elevation, when
the shot is fired horizontally, I am not so cer-
tain that some force, less than infinite, would
not carry the projectile some distance; thus
not even a cannon can fire a shot in a perfectly
horizontal direction, or as we say, point blank,
that is, with no elevation at all. Here, I admit,
there is some room for doubt. The fact I do not
deny outright, because of another phenomenon
apparently no less remarkable, but yet one for
which I have conclusive evidence. This phen-
omenon is the impossibility of stretching a rope
in such a way that it shall be at once straight
and parallel to the horizon; the fact is that the
cord always sags and bends and that no force is
sufficient to stretch it perfectly straight.
SALV. In this case of the rope then, Sagredo,
you cease to wonder at the phenomenon be-
cause you have its demonstration; but if we
consider it with more care we may possibly dis-
cover some correspondence between the case of
the gun and that of the string. The curvature
of the path of the shot fired horizontally ap-
pears to result from two forces, one (that of the
weapon) drives it horizontally and the other
(its own weight) draws it vertically downward.
So in stretching the rope you have the force
which pulls it horizontally and its own weight
which acts downwards. The circumstances in
these two cases are, therefore, very similar. If
then you attribute to the weight of the rope a
power and energy sufficient to oppose and over-
come any stretching force, no matter how great,
why deny this power to the bullet ?
Besides I must tell you something which will
both surprise and please you, namely, that a
cord stretched more or less tightly assumes a
curve which closely approximates the para-
bola. This similarity is clearly seen if you draw a
parabolic curve on a vertical plane and then in-
vert it so that the apex will lie at the bottom
and the base remain horizontal; for, on hang-
ing a chain below the base, one end attached to
each extremity of the base, you will observe
that, on slackening the chain more or less, it
bends and fits itself to the parabola; and the
coincidence is more exact in proportion as the
parabola is drawn with less curvature or, so to
speak, more stretched; so that using parabolas
described with elevations less than 45° the chain
fits its parabola almost perfectly.
SAGR. Then with a fine chain one would be
able to quickly draw many parabolic lines upon
a plane surface.
SALV. Certainly, and with no small advan-
tage as I shall show you later.
SIMP. But before going further, I am anxious
to be convinced at least of that proposition of
which you say that there is a rigid demonstra-
tion; I refer to the statement that it is impos-
sible by any force whatever to stretch a cord so
that it will lie perfectly straight and horizontal.
SAGR. I will see if I can recall the demonstra-
tion; but in order to understand it, Simplicio,
it will be necessary for you to take for granted
concerning machines what is evident not alone
from experiment but also from theoretical con-
siderations, namely, that the velocity of a mov-
ing body, even when its force is small, can over-
come a very great resistance exerted by a slow-
ly moving body, whenever the velocity of the
moving body bears to that of the resisting body
a greater ratio than the resistance of the resist-
ing body to the force of the moving body.
SIMP. This I know very well for it has been
demonstrated by Aristotle in his Questions in
Mechanics; it is also clearly seen in the lever and
the steelyard where a counterpoise weighing
not more than 4 pounds will lift a weight of
400, provided that the distance of the counter-
poise from the axis about which the steelyard
rotates be more than one hundred times as
great as the distance between this axis and the
point of support for the large weight. This is
true because the counterpoise in its descent
traverses a space more than one hundred times
as great as that moved over by the large weight
in the same time; in other words, the small
counterpoise moves with a velocity which is
more than one hundred times as great as that
of the large weight.
SAGR. You are quite right; you do not hesi-
tate to admit that however small the force of
the moving body it will overcome any resist-
ance, however great, provided it gains more in
velocity than it loses in force and weight. Now
let us return to the case of the cord. In the ac-
companying figure ab represents a line passing
through two fixed points a and b; at the ex-
tremities of this line hang, as you see, two large
weights c and d> which stretch it with great
force and keep it truly straight, seeing that it
THE TWO NEW SCIENCES
259
is merely a line without weight. Now I wish to
remark, that if from the middle point of this
line, which we may call e, you suspend any
small weight, say ^, the line ab will yield to-
ward the point /and on account of its elonga-
tion will compel the two heavy weights c and d
to rise. This I shall demonstrate as follows: with
the points a and b as centres describe the two
quadrants, eig and elm; now since the two semi-
diameters at and bl are equal to ae and eb, the
remainders ft and //a re the excesses of the lines
over ae and eb; they therefore deter-
Fig. 126
mine the rise of the weights c and dy assuming
of course that the weight h has taken the posi-
tion/ But the weight h will take the position/
whenever the line ef which represents the de-
scent of h bears to the line// — that is, to the
rise of the weights c and d — a ratio which is
greater than the ratio of the weight of the two
large bodies to that of the body h. Even when
the weights of c and dart very great and that of
h very small this will happen; for the excess of
the weights c and d over the weight of h can
never be so great but that the excess of the tan-
gent efovcr the segment// may be proportional-
ly greater. This may be proved as follows: Draw
a circle of diameter ga/ : draw the line bo such that
the ratio of its length to another length c,c>d, is
the same as the ratio of the weights c and d to
the weight h. Since c>d, the ratio of bo to d is
greater than that of bo to c. Take be a third
proportional to ob and d: prolong the diameter
gi to a point /such ihatgt:if=oc:el>; and from
the point /draw the tangent Jh; then since we
already have oe:eb~gi:if> we shall obtain, by
compounding ratios, ob:eb=gf:if. But d is a
mean proportional between ob and be; while nf
is a mean proportional between gf and ft.
Hence nf bears to// the same ratio as that of cb
to d, which is greater than that of the weights
rand d to the weight h. Since then the descent,
or velocity, of the weight h bears to the rise, or
velocity, of the weights c and d a greater ratio
than the weight of the bodies c and d bears to
the weight of h, it is clear that the weight h
will descend and the line ab will cease to be
straight and horizontal.
And now this which happens in the case of a
weightless cord ab when any small weight h is
attached at the point e, happens also when the
cord is made of ponderable matter but without
any attached weight; because in this case the
material of which the cord is composed func-
tions as a suspended weight.
SIMP. I am fully satisfied. So now Salviati can
explain, as he promised, the advantage of such
a chain and, afterwards, present the specula-
tions of our Academician on the subject of im-
pulsive forces.
SALV. Let the preceding discussions suffice
for to-day; the hour is already late and the time
remaining will not permit us to clear up the
subjects proposed; we may therefore postpone
our meeting until another and more opportune
occasion.
SAGR. I concur in your opinion, because after
various conversations with intimate friends of
our Academician I have concluded that this
question of impulsive forces is very obscure,
and I think that, up to the present, none of
those who have treated this subject have been
able to clear up its dark corners which lie al-
most beyond the reach of human imagina-
tion; among the various views which I have
heard expressed one, strangely fantastic, re-
mains in my memory, namely, that impulsive
forces are indeterminate, if not infinite. Let us,
therefore, await the convenience of Salviati.
Meanwhile, tell me what is this which follows
the discussion of projectiles.
SALV. These are some theorems pertaining to
the centres of gravity of solids, discovered by
our Academician in his youth, and undertaken
by him because he considered the treatment of
Federigo Comandino to be somewhat incom-
plete. The propositions which you have before
you would, he thought, meet the deficiencies
of Comandino's book. The investigation was
260
GALILEO GALILEI
undertaken at the instance of the Illustrious
Marquis Guidobaldo dal Monte, a very distin-
guished mathematician of his day, as is eviden-
ced by his various publications. To this gentle-
man our Academician gave a copy of this work,
hoping to extend the investigation to other
solids not treated by Comandino. But a little
later there chanced to fall into his hands the
book of the great geometrician, Luca Valerio,
where he found the subject treated so com-
pletely that he left off his own investigations,
although the methods which he employed were
quite different from those of Valerio.
SAGR. Please be good enough to leave this
volume with me until our next meeting so that
I may be able to read and study these proposi-
tions in the order in which they are written.
SALV. It is a pleasure to comply with your
request and I only hope that the propositions
will be of deep interest to you.
WILLIAM HARVEY
BIOGRAPHICAL NOTE
WILLIAM HARVEY, 1578-1657
HARVEY was born at Folkestone on April i,
1578, the eldest of the seven sons of Thomas
Harvey, a prosperous Kentish yeoman. At the
age of ten he was sent to the King's School
at Canterbury and five years later to Caius-
Gonvil College, Cambridge, where he took his
A.B. degree in 1597. To prepare himself for a
medical career he went to the University of
Padua, then the most celebrated school of
medicine. Harvey was there while Galileo was
achieving his first fame at Padua. He fol-
lowed the anatomy lectures of the great Fa-
bricius of Aquapendente and in the spring of
1602 took his degree at Padua; later that
same year he was made a Doctor of Medicine
at Cambridge.
Shortly afterwards, Harvey settled in Lon-
don, married the daughter of Dr. Lancelot
Browne, Queen Elizabeth's physician, and be-
gan to practise medicine. In 1604 he became
a candidate of the Royal College of Physicians
and was duly admitted a fellow three years
later. Upon the recommendation of the king
and the president of the college, he was ap-
pointed in 1609 assistant physician of St.
Bartholomew's Hospital and in the following
year succeeded to the post of physician. His
practice prospered, and, although Aubrey,
who knew Harvey, says that his anatomy was
better than his therapy, it is known that he
performed difficult surgical operations and had
many illustrious patients, among them Francis
Bacon and King James I, to whom he became
physician extraordinary.
Upon his appointment as the Lumleian lec-
turer at the College of Physicians in 1615, Har-
vey began his lectures on anatomy in which he
made known his work on the motions of the
heart and blood. In his lectures he professed
"to learn and teach anatomy, not from books,
but from dissections, not from the positions of
the philosophers but from the fabric of nature";
and during his lifetime he dissected more than
eighty kinds of animals. His teaching also
showed his wide knowledge of books. He knew
all the anatomists from Vesalius to his own
time; he had studied Aristotle, whom he quotes
more often than any other author, and Galen;
he was especially fond of Virgil, had read Plau-
tus, Horace, Caesar, Cicero, Vitruvius, and St.
Augustine, and was thoroughly familiar with
the Bible.
In 1628, after "nine years and more" of
teaching, Harvey published his work on the
circulation of the blood, Exerdtatio Anatomica
de Motu Cordis et Sanguims in Animalibus. The
book was dedicated to Charles I, whom Harvey
served as physician. It immediately attracted
wide attention, although at first, and particu-
larly on the continent, it was mostly of an ad-
verse character. Harvey for the most part left
the defense of his work to his supporters, and
he lived to see his teaching generally accepted.
His friend, Hobbes, declared that Harvey was
"the only one I know who has overcome public
odium and established a new doctrine during
his own lifetime."
After the publication of his work Harvey
became more closely associated with Charles I,
and until 1646 his fortunes were involved with
those of the king. By the king's command he re-
linquished his functions at the College of Phy-
sicians in 1629 to accompany James Stuart, the
young duke of Lennox, on his travels to the
continent. Four years later he went to Nurem-
berg and Rome with the Earl of Arundel, who
had been sent as an ambassador to the German
emperor. As royal physician, he several times
attended the king on his journeys. Despite his
close connection with king and court, Harvey
himself seems to have taken little interest in
politics. In 1641 he still attended the king not
only with the consent but also at the desire of
parliament^ But with the outbreak of war be-
tween the king and parliament, Harvey be-
came identified with the royal cause. At the
battle of Edgehill, Aubrey reports that he was
given charge of the Prince of Wales and the
Duke of York but was so little concerned with
the battle that "he withdrew with them under
a hedge and took out of his pocket a book and
read." Harvey went to Oxford with the re-
treating royal forces in 1642 and remained
there until the surrender of that city in 1646.
263
264
BIOGRAPHICAL NOTE
He then returned to London and for the rest
of his life lived there with his brothers, who
were eminent merchants.
During the fifteen years that Harvey was in
close attendance upon the king, he continued
to pursue his medical investigations. In study-
ing the process of generation he enjoyed the in-
terest and support of Charles I, who not only
placed the royal deer parks at his disposal, but
also watched his demonstration of the growth
of the chick with the same interest that he had
shown for the movements of the heart. Even the
Civil War did not completely interrupt his re-
search. He notes that his "enemies abstracted
from my museum the fruits of many years of
toil" with the result that "many observations,
particularly on the generation of insects, have
perished, with detriment, I venture to say, to
the republic of letters." Despite this loss, he
had collected a large number of observations
and had embodied the results of his investiga-
tions in a treatise. Finally, in 1651 his friend
and disciple, George Ent, obtained the manu-
scripts and with the author's permission made
public the work on generation, Exercitationes de
Generations Animalium.
This was the last of Harvey's labors. He had
now reached his seventy- third year and was
honored at home and abroad. Hb college at
Cambridge voted a statue in his honor, and the
College of Physicians in 1654 elected him presi-
dent, an office he declined because of age. He
had already served three terms as censor (1613,
1625, 1629), and in that capacity, together
with three of his colleagues, had supervised
practitioners, taken necessary proceedings
against quacks, and inspected apothecaries.
The same year that he was offered the presi-
dency he built and equipped a library for the
College, to which in 1656 he also made over
his property in Essex with provision for a
salary to the college librarian and the endow-
ment of an annual oration. This address, ac-
cording to Harvey's orders, is to exhort the
fellows "to search out and study the secrets of
nature by way of experiment, and also for the
honor of the profession to continue mutual
love and affection among themselves."
Although afflicted by the gout, Harvey en-
joyed the active use of all his faculties until his
eightieth year. On June 3, 1657, he was at-
tacked by paralysis and though deprived of
speech was able to send for his nephews and
distribute his personal things among them. He
died the same evening and was buried with
great honor in Hempstead Church, Essex.
CONTENTS
BIOGRAPHICAL NOTE
AN ANATOMICAL DISQUISITION ON
THE MOTION OF THE HEART AND
BLOOD IN ANIMALS
DEDICATIONS
INTRODUCTION
267
268
CHAP-
1. The author's motives for writing 273
2. Of the motions of the heart, as seen in the dis-
section of living animals 274
3. Of the motions of arteries, as seen in the dissec-
tion of living animals 275
4. Of the motion of the heart and its auricles, as
seen in the bodies of living animals 276
5. Of the motion, action, and office of the heart 278
6. Of the course by which the blood is carried
from the vena cava into the arteries, or from
the right into the left ventricle of the heart 280
7. The blood percolates the substance of the lungs
from the right ventricle of the heart into the
pulmonary veins and left ventricle 283
8. Of the quantity of blood passing through the
heart from the veins to the arteries; and of the
circular motion of the blood 285
9. That there is a circulation of the blood is con-
firmed from the first proposition 286
10. The first position: of the quantity of blood
passing from the veins to the arteries. And that
there is a circuit of the blood, freed from objec-
tions, and farther confirmed by experiment 288
11. The second position is demonstrated 289
12. That there is a circulation of the blood is shown
from the second position demonstrated 292
13. The third position is confirmed: and the circu-
lation of the blood is demonstrated from it 293
14. Conclusion of the demonstration of the circu-
lation 295
15. The circulation of the blood is further con-
firmed by probable reasons 296
16. The circulation of the blood is further proved
from certain consequences 297
17. The motion and circulation of the blood are
confirmed from the particulars apparent in the
structure of the heart, and from those things
which dissection unfolds 299
THE FIRST ANATOMICAL DISQUISITION
ON THE CIRCULATION OF THE BLOOD,
ADDRESSED TO JOHN RIOLAN 305
263 A SECOND DISQUISITION TO JOHN RIO-
LAN; IN WHICH MANY OBJECTIONS TO
THE CIRCULATION OF THE BLOOD
ARE REFUTED 313
ANATOMICAL EXERCISES ON
THE GENERATION OF ANIMALS
DEDICATION 329
INTRODUCTION 331
Of the manner and order of acquiring knowledge 332
Of the same matters, according to Aristotle 333
Of the method to be pursued in studying gen-
eration 335
ON ANIMAL GENERATION
EXERCISE
1. Wherefore we begin with the history of the
hen's egg 338
2. Of the seat of generation 338
3. Of the upper part of the hen's uterus, or the
ovary 339
4. Of the infundibulum 342
5. Ot the external portion of the uterus of the
common fowl 343
6. Of the uterus of the fowl 347
7. Of the abdomen of the common fowl and of
other birds 350
8. Of the situation and structure of the remaining
parts of the fowl's uterus 351
9. Of the extrusion of the egg, or parturition of
the fowl, in general 353
10. Of the increase and nutrition of the egg 353
11. Of the covering or shell of the egg 354
12. Of the remaining parts of the egg 357
13. Of the diversities of eggs 359
14. Of the production of the chick from the egg of
the hen 363
15. The first examination of the egg; or of the effect
of the first day's incubation upon the egg 365
16. Second inspection of the egg 366
17. The third inspection of the egg 368
18. The fourth inspection of the egg 371
19. The fifth inspection of the egg 375
20. The sixth inspection 377
21. The inspection after the tenth day 378
22. The inspection after the fourteenth day 379
23. Of the exclusion of the chick, or the birth from
the egg 381
24. Of twin-bearing eggs 382
265
2(56 CONTENTS
25. Certain deductions from the preceding history
of the egg 383 48,
26. Of the nature of the egg 383
27. The egg is not the product of the uterus, but of 49.
the vital principle 388
28. The egg is not produced without the hen 390 50.
29. Of the manner, according to Aristotle, in which
a perfect and fruitful egg is produced by the 51,
male and female fowl 391
30. Of the uses of this disquisition on fecundity 393 52.
31. The egg is not produced by the cock and hen in 53.
the way Aristotle would have it 394
32. Nor in the manner imagined by physicians 394 54.
33. The male and the female are alike efficient in
the business of generation 395 55.
34. Of the matter of the egg, in opposition to the
Aristotelians and the medical writers 396 56.
35. In how far is the fowl efficient in the generation
of the egg, according to Aristotle? And where- 57.
fore is the concurrence of the male required ? 397
36. The perfect hen's egg is of two colours 398 58.
37. Of the manner in which the egg is increased by 59.
the albumen 399 60.
38. Of what the cock and hen severally contribute 61.
to the production of the egg 400 62.
39. Of the cock and the particulars most remark- 63.
able in his constitution 401 64.
40. Of the hen 402
41. Of the sense in which the hen may be called the
"prime efficient": and of her parturition 405 65.
42. Of the manner in which the generation of the 66.
chick takes place from the egg. 407 67.
43. In how many ways the chick may be said to be
formed from the egg 408
44. Fabncius is mistaken with regard to the matter 68.
of the generation of the chick in ovo 409 69.
45. What is the material of the chick, and how it is
formed in the egg 412 70,
46. Of the efficient cause of the generation of the
chick and foetus 415 71,
47. Of the manner in which the efficient cause of 72.
the chick acts, according to Aristotle 417
The opinion of Fabricius on the efficient cause
of the chick is refuted 419
The inquiry into the efficient cause of the chick
is one of great difficulty 421
Of the efficient cause of animals, and its con-
ditions 424
Of the order of generation; and, first, of the
primary genital particle 429
Of the blood as prime element in the body 432
Of the inferences deducible from the course of
the umbilical vessels in the egg 438
Of the order of the parts in generation from an
egg, according to Fabricius 441
Of the order of the parts according to Aris-
totle 445
Of the order of the parts in generation as it
appears from observation 449
Of certain paradoxes and problems to be con-
sidered in connexion with this subject 454
Of the nutrition of the chick in ovo 458
Of the uses of the entire egg 461
Of the uses of the yelk and albumen 462
Of the uses of the other parts of the egg 467
An egg is the common origin of all animals 468
Of the generation of viviparous animals 470
The generation of viviparous animals in gen-
eral is illustrated from the history of that of the
hind and doe, and the reason of this selection 472
Of the uterus of the hind and doe 473
Of the intercourse of the hind and doe 476
Of the constitution or change that takes place
in the uterus of the deer in the course of the
month of September 477
Of what takes place in the month of October 478
Of what takes place in the uterus of the doe
during the month of November 479
Of the conception of the deer in the course oi
the month of December 484
Of the innate heat 488
Of the pnmigenial moisture 494
An Anatomical Disquisition on the
Motion of the Heart and Blood in Animals
To the Most Illustrious and Indomitable Prince,
CHARLES,
KING OF GREAT BRITAIN, FRANCE, AND IRELAND,
DEFENDER OF THE FAITH
MOST ILLUSTRIOUS PRINCE!
The heart of animals is the foundation of their life, the sovereign of every-
thing within them, the sun of their microcosm, that upon which all growth de-
pends, from which all power proceeds. The King, in like manner, is the founda-
tion of his kingdom, the sun of the world around him, the heart of the repub-
lic, the fountain whence all power, all grace doth flow. What I have here written
of the motions of the heart I am the more emboldened to present to your Ma-
jesty, according to the custom of the present age, because almost all things
human are done after human examples, and many things in a King are after the
pattern of the heart. The knowledge of his heart, therefore, will not be useless
to a Prince, as embracing a kind of Divine example of his functions — and it
has still been usual with men to compare small things with great. Here, at all
events, best of Princes, placed as you are on the pinnacle of human affairs, you
may at once contemplate the prime mover in the body of man, and the emblem
of your own sovereign power. Accept therefore, with your wonted clemency, I
most humbly beseech you, illustrious Prince, this, my new Treatise on the
Heart; you, who are yourself the new light of this age, and indeed its very
heart; a Prince abounding in virtue and in grace, and to whom we gladly refer
all the blessings which England enjoys, all the pleasure we have in our lives.
Your Majesty's most devoted servant,
WILLIAM HARVEY
[London .... 1628.]
TO HIS VERY DEAR FRIEND, DOCTOR ARGENT, THE EXCELLENT AND
ACCOMPLISHED PRESIDENT OF THE ROYAL COLLEGE OF PHYSICIANS,
AND TO OTHER LEARNED PHYSICIANS, HIS MOST ESTEEMED COLLEAGUES
I have already and repeatedly presented you, say entreaties, of many, and here present them
my learned friends, with my new views of the for general consideration in this treatise,
motion and function of the heart, in my ana- Were not the work indeed presented through
tomical lectures; but having now for nine years you, my learned friends, I should scarce hope
and more confirmed these views by multiplied that it could come out scatheless and corn-
demonstrations in your presence, illustrated plete; for you have in general been the faithful
them by arguments, and freed them from the witnesses of almost all the instances from which
objections of the most learned and skilful anato- I have either collected the truth or confuted
mists, I at length yield to the requests, I might error; you have seen my dissections, and at my
268
WILLIAM HARVEY
demonstrations of all that I maintain to be
objects of sense, you have been accustomed to
stand by and bear me out with your testimony.
And as this book alone declares the blood to
course and revolve by a new route, very differ-
ent from the ancient and beaten pathway trod-
den for so many ages, and illustrated by such a
host of learned and distinguished men, I was
greatly afraid lest I might be charged with pre-
sumption did I lay my work before the public
at home, or send it beyond seas for impression,
unless I had first proposed its subject to you,
had confirmed its conclusions by ocular demon-
strations in your presence, had replied to your
doubts and objections, and secured the assent
and support of our distinguished President. For
I was most intimately persuaded, that if I could
make good my proposition before you and our
College, illustrious by its numerous body of
learned individuals, I had less to fear from oth-
ers; I even ventured to hope that I should have
the comfort of finding all that you had granted
me in your sheer love of truth, conceded by
others who were philosophers like yourselves.
For true philosophers, who are only eager for
truth and knowledge, never regard themselves
as Already so thoroughly informed, but that
they welcome further information from whom-
soever and from whencesoever it may come;
nor are they so narrow-minded as to imagine
any of the arts or sciences transmitted to us by
the ancients, in such a state of forwardness or
completeness, that nothing is left for the in-
genuity and industry of others; very many, on
the contrary, maintain that all we know is still
infinitely less than all that still remains un-
known; nor do philosophers pin their faith to
others' precepts in such wise that they lose their
liberty, and cease to give credence to the con-
clusions of their proper senses. Neither do they
swear such fealty to their mistress Antiquity,
that they openly, and in sight of all, deny and
desert their friend Truth. But even as they see
that the credulous and vain are disposed at the
first blush to accept and to believe everything
that is proposed to them, so do they observe
that the dull and unintellectual are indisposed
to see what lies before their eyes, and even to
deny the light of the noonday sun. They teach
us in our course of philosophy as sedulously to
avoid the fables of the poets and the fancies of
the vulgar, as the false conclusions of the scep-
tics. And then the studious, and good, and true,
never suffer their minds to be warped by the
passions of hatred and envy, which unfit men
duly to weigh the arguments that are advanced
in behalf of truth, or to appreciate the proposi-
tion that is even fairly demonstrated; neither
do they think it unworthy of them to change
their opinion if truth and undoubted demon-
stration require them so to do; nor do they
esteem it discreditable to desert error, though
sanctioned by the highest antiquity; for they
know full well that to err, to be deceived, is hu-
man; that many things are discovered by acci-
dent, and that many may be learned indiffer-
ently from any quarter, by an old man from a
youth, by a person of understanding from one
of inferior capacity.
My dear colleagues, I had no purpose to swell
this treatise into a large volume by quoting the
names and writings of anatomists, or to make a
parade of the strength of my memory, the ex-
tent of my reading, and the amount of my
pains; because I profess both to learn and to
teach anatomy, not from books but from dis-
sections; not from the positions of philosophers
but from the fabric of nature; and then because
I do not think it right or proper to strive to
take from the ancients any honour that is their
due, nor yet to dispute with the moderns, and
enter into controversy with those who have ex-
celled in anatomy and been my teachers. I
would not charge with wilful falsehood anyone
who was sincerely anxious for truth, nor lay it
to anyone's door as a crime that he had fallen
into error. I avow myself the partisan of truth
alone; and I can indeed say that I have used all
my endeavours, bestowed all my pains on an
attempt to produce something that should be
agreeable to the good, profitable to the learned,
and useful to letters.
Farewell, most worthy Doctors,
And think kindly of your Anatomist,
WILLIAM HARVEY
INTRODUCTION
As we are about to discuss the motion, action,
and use of the heart and arteries, it is impera-
tive on us first to state what has been thought
of these things by others in their writings, and
what has been held by the vulgar and by tradi-
tion, in order that what is true may be con-
firmed, and what is false set right by dissection,
multiplied experience, and accurate observation.
Almost all anatomists, physicians, and phi-
losophers, up to the present time, have sup-
posed, with Galen, that the object of the pulse
was the same as that of respiration, and only
differed in one particular, this being conceived
to depend on the animal, the respiration on the
vital faculty; the two, in all other respects,
MOTION OF THE HEART
269
whether with reference to purpose or to mo-
tion, comporting themselves alike. Whence it
is affirmed, as by Hieronymus Fabricius of
Aquapendente, in his book on Respiration,
which has lately appeared, that as the pulsation
of the heart and arteries does not suffice for the
ventilation and refrigeration of the blood, there-
fore were the lungs fashioned to surround the
heart. From this it appears that whatever has
hitherto been said upon the systole and dias-
tole, on the motion of the heart and arteries,
has been said with especial reference to the
lungs.
But as the structure and movements of the
heart differ from those of the lungs, and the
motions of the arteries from those of the chest,
so seems it likely that other ends and offices will
thence arise, and that the pulsations and uses of
the heart, likewise of the arteries, will differ in
many respects from the heavings and uses of
the chest and lungs. For did the arterial pulse
and the respiration serve the same ends; did the
arteries in their diastole take air into their cavi-
ties, as commonly stated, and in their systole
emit fuliginous vapours by the same pores of
the flesh and skin; and further, did they, in the
time intermediate between the diastole and the
systole, contain air, and at all times either air,
or spirits, or fuliginous vapours, what should
then be said to Galen, who wrote a book on
purpose to show that by nature the arteries
contained blood, and nothing but blood; neither
spirits nor air, consequently, as may be readily
gathered from the experiments and reasonings
contained in the same book ? Now if the arteries
are filled in the diastole with air then taken into
them (a larger quantity of air penetrating when
the pulse is large and full), it must come to pass
that if you plunge into a bath of water or of oil
when the pulse is strong and full, it ought forth-
with to become either smaller or much slower,
since the circumambient bath will render it
either difficult or impossible for the air to pen-
etrate. In like manner, as all the arteries, those
that are deep-seated as well as those that are
superficial, are dilated at the same instant, and
with the same rapidity, how were it possible
that air should penetrate to the deeper parts as
freely and quickly through the skin, flesh, and
other structures, as through the mere cuticle ?
And how should the arteries of the foetus draw
air into their cavities through the abdomen of
the mother and the body of the womb? And
how should seals, whales, dolphins, and other
cetaceans, and fishes of every description, liv-
ing in the depths of the sea, take in and emit
air by the diastole and systole of their arteries
through the infinite mass of waters ? For to say
that they absorb the air that is infixed in the
water, and emit their fumes into this medium,
were to utter something very like a mere fig-
ment. And if the arteries in their systole expel
fuliginous vapours from their cavities through
the pores of the flesh and skin, why not the
spirits, which are said to be contained in these
vessels, at the same time, since spirits are much
more subtile than fuliginous vapours or smoke ?
And further, if the arteries take in and cast out
air in the systole and diastole, like the lungs in
the process of respiration, wherefore do they
not do the same thing when a wound is made
in one of them, as is done in the operation of
arteriotomy ? When the windpipe is divided, it
is sufficiently obvious that the air enters and
returns through the wound by two opposite
movements; but when an artery is divided, it
is equally manifest that blood escapes in one
continuous stream, and that no air either enters
or issues. If the pulsations of the arteries fan
and refrigerate the several parts of the body as
the lungs do the heart, how comes it, as is com-
monly said, that the arteries carry the vital
blood into the different parts, abundantly
charged with vital spirits, which cherish the
heat of these parts, sustain them when asleep,
and recruit them when exhausted? And how
should it happen that, if you tie the arteries,
immediately the parts not only become torpid,
and frigid, and look pale, but at length cease
even to be nourished ? This, according to Galen,
is because they are deprived of the heat which
flowed through all parts from the heart, as its
source; whence it would appear that the arteries
rather carry warmth to the parts than serve for
any fanning or refrigeration. Besides, how can
the diastole draw spirits from the heart to warm
the body and its parts, and, from without,
means of cooling or tempering them ? Still fur-
ther, although some affirm that the lungs, ar-
teries, and heart have all the same offices, they
yet maintain that the heart is the workshop of
the spirits, and that the arteries contain and
transmit them; denying, however, in opposi-
tion to the opinion of Columbus, that the lungs
can either make or contain spirits; and then
they assert, with Galen, against Erasistratus,
that it is blood, not spirits, which is contained
in the arteries.
These various opinions are seen to be so in-
congruous and mutually subversive, that every
one of them is not unjustly brought under sus-
picion. That it is blood and blood alone which
270
WILLIAM HARVEY
is contained in the arteries is made manifest by
the experiment of Galen, by arteriotomy, and
by wounds; for from a single artery divided, as
Galen himself affirms in more than one place,
the whole of the blood may be withdrawn in
the course of half an hour, or less. The experi-
ment of Galen alluded to is this: "If you include
a portion of an artery between two ligatures,
and slit it open lengthways, you will find noth-
ing but blood"; and thus he proves that the ar-
teries contain blood only. And we too may be
permitted to proceed by a like train of reason-
ing: if we find the same blood in the arteries
that we find in the veins, which we have tied in
the same way, as I have myself repeatedly as-
certained, both in the dead body and in living
animals, we may fairly conclude that the ar-
teries contain the same blood as the veins, and
nothing but the same blood. Some, whilst they
attempt to lessen the difficulty here, affirming
that the blood is spirituous and artenous, vir-
tually concede that the office of the arteries
is to carry blood from the heart into the whole
of the body, and that they are therefore filled
with blood; for spirituous blood is not the less
blood on that account. And then no one denies
that the blood as such, even the portion of it
which flows in the veins, is imbued with spirits.
But if that portion which is contained in the ar-
teries be richer in spirits, it is still to be be-
lieved that these spirits are inseparable from
the blood, like those in the veins; that the blood
and spirits constitute one body (like whey and
butter in milk, or heat [and water] in hot wa-
ter), with which the arteries are charged, and
for the distribution of which from the heart
they are provided, and that this body is noth-
ing else than blood. But if this blood be said to
be drawn from the heart into the arteries by
the diastole of these vessels, it is then assumed
that the arteries by their distension are filled
with blood, and not with the ambient air, as
heretofore; for if they be said also to become
filled with air from the ambient atmosphere,
how and when, I ask, can they receive blood
from the heart? If it be answered: during the
systole; I say, that seems impossible; the ar-
teries would then have to fill whilst they con-
tracted; in other words, to fill, and yet not be-
come distended. But if it be said: during the
diastole, they would then, and for two opposite
purposes, be receiving both blood and air, and
heat and cold; which is improbable. Further,
when it is affirmed that the diastole of the heart
and arteries is simultaneous, and the systole of
the two is also concurrent, there is another in-
congruity. For how can two bodies mutually
connected, which are simultaneously distended,
attract or draw anything from one another; or,
being simultaneously contracted, receive any-
thing from each other? And then, it seems im-
possible that one body can thus attract another
body into itself, so as to become distended, see-
ing that to be distended is to be passive, un-
less, in the manner of a sponge, previously com-
pressed by an external force, whilst it is return-
ing to its natural state. But it is difficult to con-
ceive that there can be anything of this kind in
the arteries. The arteries dilate, because they
are filled like bladders or leathern bottles; they
are not filled because they expand like bellows.
This I think easy of demonstration; and indeed
conceive that I have already proved it. Never-
theless, in that book of Galen headed Quod
sanguis continetur in arteriis, he quotes an ex-
periment to prove the contrary: An artery,
having been exposed, is opened longitudinally,
and a reed or other pervious tube, by which the
blood is prevented from being lost, and the
wound is closed, is inserted into the vessel
through the opening. "So long," he says, "as
things are thus arranged, the whole artery will
pulsate; but if you now throw a ligature about
the vessel and tightly compress its tunics over
the tube, you will no longer see the artery beat-
ing beyond the ligature." I have never per-
formed this experiment of Galen's, nor do I
think that it could very well be performed in
the living body, on account of the profuse flow
of blood that would take place from the vessel
which was operated on; neither would the tube
effectually close the wound in the vessel with-
out a ligature; and I cannot doubt but that the
blood would be found to flow out between the
tube and the vessel. Still Galen appears by this
experiment to prove both that the pulsative
faculty extends from the heart by the walls of
the arteries, and that the arteries, whilst they
dilate, are filled by that pulsific force, because
they expand like bellows, and do not dilate be-
cause they are filled like skins. But the con-
trary is obvious in arteriotomy and in wounds;
for the blood spurting from the arteries escapes
with force, now farther, now not so far, alter-
nately, or in jets; and the jet always takes place
with the diastole of the artery, never with the
systole. By which it clearly appears that the ar-
tery is dilated by the impulse of the blood; for
of itself it would not throw the blood to such a
distance, and whilst it was dilating; it ought
rather to draw air into its cavity through the
wound, were those things true that are com-
monly stated concerning the uses of the arter-
ies. Nor let the thickness of the arterial tunics
impose upon us, and lead us to conclude that
the pulsative property proceeds along them
from the heart. For in several animals the arter-
ies do not apparently differ from the veins;
and in extreme parts of the body, where the ar-
teries are minutely subdivided, as in the brain,
the hand, &c., no one could distinguish the ar-
teries from the veins by the dissimilar charac-
ters of their coats; the tunics of both are iden-
tical. And then, in an aneurism proceeding
from a wounded or eroded artery, the pulsa-
tion is precisely the same as in the other ar-
teries, and yet it has no proper arterial tunic.
This the learned Riolanus testifies to, along
with me, in his Seventh Book.
Nor let any one imagine that the uses of the
pulse and the respiration are the same, because
under the influence of the same causes, such as
running, anger, the warm bath, or any other
heating thing, as Galen says, they become more
frequent and forcible together. For, not only is
experience in opposition to this idea, though
Galen endeavours to explain it away, when we
see that with excessive repletion the pulse beats
more forcibly, whilst the respiration is dimin-
ished in amount; but in young persons the pulse
is quick, whilst respiration is slow. So is it also
in alarm, and amidst care, and under anxiety of
mind; sometimes, too, in fevers, the pulse is
rapid, but the respiration is slower than usual.
These and other objections of the same kind
may be urged against the opinions mentioned.
Nor are the views that are entertained of the
offices and pulse of the heart, perhaps, less
bound up with great and most inextricable dif-
ficulties. The heart, it is vulgarly said, is the
fountain and workshop of the vital spirits, the
centre from whence life is dispensed to the
several parts of the body; and yet it is denied
that the right ventricle makes spirits; it is
rather held to supply nourishment to the lungs;
whence it is maintained that fishes are without
any right ventricle (and indeed every animal
wants a right ventricle which is unfurnished
with lungs), and that the right ventricle is pres-
ent solely for the sake of the lungs.
i. Why, I ask, when we see that the structure
of both ventricles is almost identical, there
being the same apparatus of fibres, and braces,
and valves, and vessels, and auricles, and in
both the same infarction of blood, in the sub-
jects of our dissections, of the like black col-
our, and coagulated — why, I say, should their
uses be imagined to be different, when the ac-
MOTION OF THE HEART 271
tion, motion, and pulse of both are the same ?
If the three tricuspid valves placed at the en-
trance into the right ventricle prove obstacles
to the reflux of the blood into the vena cava,
and if the three semilunar valves which are
situated at the commencement of the pulmon-
ary artery be there, that they may prevent the
return of the blood into the ventricle; where-
fore, when we find similar structures in con-
nexion with the left ventricle, should we deny
that they are there for the same end, of pre-
venting here the egress, there the regurgita-
tion of the blood ?
2. And again, when we see that these struc-
tures, in point of size, form, and situation, are
almost in every respect the same in the left as
in the right ventricle, wherefore should it be
maintained that things are here arranged in
connexion with the egress and regress of spirits,
there, i.e., in the right, of blood. The same ar-
rangement cannot be held fitted to favour or
impede the motion of blood and of spirits in-
differently.
3. And when we observe that the passages
and vessels are severally in relation to one an-
other in point of size, viz., the pulmonary ar-
tery to the pulmonary veins; wherefore should
the one be imagined destined to a private or
particular purpose, that, to wit, of nourishing
the lungs, the other to a public and general
function?
4. And, as Realdus Columbus says, how can
it be conceived that such a quantity of blood
should be required for the nutrition of the
lungs; the vessel that leads to them, the vena
arteriosa or pulmonary artery being of greater
capacity than both the iliac veins?
5. And I ask further; as the lungs are so close
at hand, and in continual motion, and the vessel
that supplies them is of such dimensions, what
is the use or meaning of the pulse of the right
ventricle ? and why was nature reduced to the
necessity of adding another ventricle for the
sole purpose of nourishing the lungs ?
When it is said that the left ventricle obtains
materials for the formation of spirits, air to
wit, and blood, from the lungs and right sinuses
of the heart, and in like manner sends spiritu-
ous blood into the aorta, drawing fuliginous
vapours from thence, and sending them by the
arteria venosa into the lungs, whence spirits
are at the same time obtained for transmission
into the aorta, I ask how, and by what means,
is the separation effected? and how comes it
that spirits and fuliginous vapours can pass
hither and thither without admixture or con-
272
WILLIAM HARVEY
fusion? If the mitral cuspidate valves do not
prevent the egress of fuliginous vapours to the
lungs, how should they oppose the escape of
air? And how should the semilunars hinder the
regress of spirits from the aorta upon each su-
pervening diastole of the heart? And, above
all, how can they say that the spirituous blood
is sent from the arteria venalis (pulmonary
veins) by the left ventricle into the lungs with-
out any obstacle to its passage from the mitral
valves, when they have previously asserted
that the air entered by the same vessel from
the lungs into the left ventricle, and have
brought forward these same mitral valves as
obstacles to its retrogression? Good God! how
should the mitral valves prevent regurgitation
of air and not of blood ?
Further, when they dedicate the vena ar-
teriosa (or pulmonary artery), a vessel of great
size, and having the tunics of an artery, to none
but a kind of private and single purpose, that,
namely, of nourishing the lungs, why should the
arteria venalis (or pulmonary vein), which is
scarcely of similar size, which has the coats of a
vein, and is soft and lax, be presumed to be
made for many — three or four, different uses?
For they will have it that air passes through this
vessel from the lungs into the left ventricle;
that fuliginous vapours escape by it from the
heart into the lungs; and that a portion of the
spirituous or spiritualized blood is distributed
by it to the lungs for their refreshment.
If they will have it that fumes and air —
fumes flowing from, air proceeding towards the
heart — are transmitted by the same conduit, I
reply that nature is not wont to institute but
one vessel, to contrive but one way for such
contrary motions and purposes, nor is anything
of the kind seen elsewhere.
If fumes or fuliginous vapours and air per-
meate this vessel, as they do the pulmonary
bronchia, wherefore do we find neither air nor
fuliginous vapours when we divide the arteria
venosa ? Why do we always find this vessel full
of sluggish blood, never of air? — whilst in the
lungs we find abundance of air remaining.
If anyone will perform Galen's experiment
of dividing the trachea of a living dog, forcibly
distending the lungs with a pair of bellows, and
then tying the trachea securely, he will find,
when he has laid open the thorax, abundance of
air in the lungs, even to their extreme invest-
ing tunic, but none in either the pulmonary
veins, or left ventricle of the heart. But did the
heart either attract air from the lungs, or did the
lungs transmit any air to the heart, in the living
dog, by so much the more ought this to be the
case in the experiment just referred to. Who,
indeed, doubts that, did he inflate the lungs of a
subject in the dissecting-room, he would in-
stantly see the air making its way by this route,
were there actually any such passage for it?
But this office of the pulmonary veins, namely,
the transference of air from the lungs to the
heart, is held of such importance, that Hieron-
ymus Fabricius of Aquapendente, maintains
the lungs were made for the sake of this vessel,
and that it constitutes the principal element in
their structure.
But I should like to be informed wherefore,
if the pulmonary vein were destined for the
conveyance of air, it has the structure of a
blood-vessel here. Nature had rather need of
annular tubes, such as those of the bronchia, in
order that they might always remain open, not
have been liable to collapse; and that they might
continue entirely free from blood, lest the liquid
should interfere with the passage of the air, as
it so obviously does when the lungs labour from
being either greatly oppressed or loaded in a
less degree with phlegm, as they are when the
breathing is performed with a sibilous or rat-
tling noise.
Still less is that opinion to be tolerated which
(as a two-fold matter, one aereal, one sanguine-
ous, is required for the composition of vital
spirits) supposes the blood to ooze through the
septum of the heart from the right to the left
ventricle by certain secret pores, and the air to
be attracted from the lungs through the great
vessel, the pulmonary vein; and which will
have it, consequently, that there are numerous
pores in the septum cordis adapted for the
transmission of the blood. But, in faith, no such
pores can be demonstrated, neither, in fact, do
any such exist. For the septum of the heart is of
a denser and more compact structure than any
portion of the body, except the bones and sin-
ews. But even supposing that there were fora-
mina or pores in this situation, how could one
of the ventricles extract anything from the
other — the left, e.g., obtain blood from the
right, when we see that both ventricles contract
and dilate simultaneously? Wherefore should
we not rather believe that the right took spirits
from the left, than that the left obtained blood
from the right ventricle, through these fora-
mina? But it is certainly mysterious and incon-
gruous that blood should be supposed to be
most commodiously drawn through a set of ob-
scure or invisible pores, and air through per-
fectly open passages, at one and the same mo-
MOTION OF THE HEART
273
ment. And why, I ask, is recourse had to secret
and invisible porosities, to uncertain and ob-
scure channels, to explain the passage of the
blood into the left ventricle, when there is so
open a way through the pulmonary veins ? I own
it has always appeared extraordinary to me
that they should have chosen to make, or
rather to imagine, a way through the thick,
hard, and extremely compact substance of the
septum cordis, rather than to take that by the
open vas venosum or pulmonary vein, or even
through the lax, soft and spongy substance of
the lungs at large. Besides, if the blood could
permeate the substance of the septum, or could
be imbibed from the ventricles, what use were
there for the coronary artery and vein, branches
of which proceed to the septum itself, to sup-
ply it with nourishment? And what is espe-
cially worthy of notice is this: if in the foetus,
where everything is more lax and soft, Nature
saw herself reduced to the necessity of bringing
the blood from the right into the left side of the
heart by the foramen ovale, from the vena
cava through the arteria venosa, how should it
be likely that in the adult she should pass it so
commodiously, and without an effort, through
the septum ventriculorum, which has now be-
come denser by age ?
Andreas Laurentius,1 resting on the author-
ity of Galen2 and the experience of Hollerius,
asserts and proves that the serum and pus in
empyema, absorbed from the cavities of the
chest into the pulmonary vein, may be ex-
pelled and got rid of with the urine and faeces
through the left ventricle of the heart and ar-
teries. He quotes the case of a certain person af-
fected with melancholia, and who suffered
from repeated fainting fits, who was relieved
from the paroxysms on passing a quantity of
turbid, fetid, and acrid urine; but he died at
last, worn out by the disease; and when the body
came to be opened after death, no fluid like
that he had micturated was discovered either
in the bladder or in the kidneys; but in the left
ventricle of the heart and cavity of the thorax
plenty of it was met with; and then Laurentius
boasts that he had predicted the cause of the
symptoms. For my own part, however, I can-
not but wonder, since he had divined and pre-
dicted that heterogeneous matter could be dis-
charged by the course he indicates, why he
could not or would not perceive, and inform us
that, in the* natural state of things, the blood
might be commodiously transferred from the
1 Book ix, Chap, n, q. 12.
2 De facts affectts, vi, 7.
lungs to the left ventricle of the heart by the
very same route.
Since, therefore, from the foregoing consider-
ations and many others to the same effect, it is
plain that what has heretofore been said con-
cerning the motion and function of the heart
and arteries must appear obscure, or inconsis-
tent or even impossible to him who carefully
considers the entire subject; it will be proper to
look more narrowly into the matter; to con-
template the motion of the heart and arteries,
not only in man, but in all animals that have
hearts; and further, by frequent appeals to
vivisection, and constant ocular inspection, to
investigate and endeavour to find the truth.
CHAPTER 1. The author's motives for writing
WHEN I first gave my mind to vivisections, as a
means of discovering the motions and uses of
the heart, and sought to discover these from ac-
tual inspection, and not from the writings of
others, I found the task so truly arduous, so full
of difficulties, that I was almost tempted to
think, with Fracastorius, that the motion of the
heart was only to be comprehended by God.
For I could neither rightly perceive at first
when the systole and when the diastole took
place, nor when and where dilatation and con-
traction occurred, by reason of the rapidity of
the motion, which in many animals is accom-
plished in the twinkling of an eye, coming and
going like a flash of lightning; so that the sys-
tole presented itself to me now from this point,
now from that; the diastole the same; and then
everything was reversed, the motions occur-
ring, as it seemed, variously and confusedly to-
gether. My mind was therefore greatly unset-
tled, nor did I know what I should myself con-
clude, nor what believe from others; I was not
surprised that Andreas Laurentius should have
said that the motion of the heart was as per-
plexing as the flux and reflux of Euripus had
appeared to Aristotle.
At length, and by using greater and daily
diligence, having frequent recourse to vivisec-
tions, employing a variety of animals for the
purpose, and collating numerous observations,
I thought that I had attained to the truth, that
I should extricate myself and escape from this
labyrinth, and that I had discovered what I so
much desired, both the motion and the use of
the heart and arteries; since which time I have
not hesitated to expose my views upon these
subjects, not only in private to my friends, but
also in public, in my anatomical lectures, after
the manner of the Academy of old.
274
WILLIAM HARVEY
These views, as usual, pleased some more,
others less; some chid and calumniated me, and
laid it to me as a crime that I had dared to de-
part from the precepts and opinion of all anato-
mists; others desired further explanations of the
novelties, which they said were both worthy of
consideration, and might perchance be found
of signal use. At length, yielding to the requests
of my friends, that all might be made partici-
pators in my labours, and partly moved by the
envy of others, who, receiving my views with
uncandid minds and understanding them indif-
ferently, have essayed to traduce me publicly,
I have been moved to commit these things to
the press, in order that all may be enabled to
form an opinion both of me and my labours.
This step I take all the more willingly, seeing
that Hieronymus Fabricius of Aquapendente,
although he has accurately and learnedly de-
lineated almost every one of the several parts of
animals in a special work, has left the heart
alone untouched. Finally, if any use or benefit
to this department of the republic of letters
should accrue from my labours, it will, perhaps,
be allowed that I have not lived idly, and, as
the old man in the comedy says:
For never yet hath any one attained
To such perfection, but that time, and place,
And use, have brought addition to his knowl-
edge;
Or made correction, or admonished him,
That he was ignorant of much which he
Had thought he knew; or led him to reject
What he had once esteemed of highest price.
So will it, perchance, be found with reference
to the heart at this time; or others, at least,
starting from hence, the way pointed out to
them, advancing under the guidance of a hap-
pier genius, may make occasion to proceed
more fortunately, and to inquire more accu-
rately.
CHAPTER 2. Of the motions of the heart, as seen in
the dissection of living animals
IN the first place, then, when the chest of a liv-
ing animal is laid open and the capsule that
immediately surrounds the heart is slit up or
removed, the organ is seen now to move, now
to be at rest; there is a time when it moves, and
a time when it is motionless.
These things are more obvious in the colder
animals, such as toads, frogs, serpents, small
fishes, crabs, shrimps, snails and shell-fish. They
also become more distinct in warm-blooded
animals, such as the dog and hog, if they be at-
tentively noted when the heart begins to flag,
to move more slowly, and, as it were, to die:
the movements then become slower and rarer,
the pauses longer, by which it is made much
more easy to perceive and unravel what the
motions really are, and how they are performed.
In the pause, as in death, the heart is soft, flac-
cid, exhausted, lying, as it were, at rest.
In the motion, and interval in which this is
accomplished, three principal circumstances
are to be noted:
1. That the heart is erected, and rises up-
wards to a point, so that at this time it strikes
against the breast and the pulse is felt exter-
nally.
2. That it is everywhere contracted, but
more especially towards the sides, so that it
looks narrower, relatively longer, more drawn
together. The heart of an eel taken out of the
body of the animal and placed upon the table
or the hand, shows these particulars; but the
same things are manifest in the heart of small
fishes and of those colder animals where the
organ is more conical or elongated.
3. The heart being grasped in the hand, it is
felt to become harder during its action. Now
this hardness proceeds from tension, precisely
as when the forearm is grasped, its tendons are
perceived to become tense and resilient when
the fingers are moved.
4. It may further be observed in fishes, and
the colder blooded animals, such as frogs, ser-
pents, &c., that the heart, when it moves, be-
comes of a paler colour, when quiescent of a
deeper blood- red colour.
From these particulars it appeared evident to
me that the motion of the heart consists in a
certain universal tension— both contraction in
the line of its fibres, and constriction in every
sense. It becomes erect, hard, and of diminished
size during its action; the motion is plainly of
the same nature as that of the muscles when
they contract in the line of their sinews and
fibres; for the muscles, when in action, acquire
vigour and tenseness, and from soft become
hard, prominent and thickened: in the same
manner the heart.
We are therefore authorized to conclude that
the heart, at the moment of its action, is at once
constricted on all sides, rendered thicker in its
parietes and smaller in its ventricles, and so
made apt to project or expel its charge of blood.
This, indeed, is made sufficiently manifest by
the fourth observation preceding, in which we
have seen that the heart, by squeezing out the
blood it contains becomes paler, and then when
MOTION OF THE HEART
275
it sinks into repose and the ventricle is filled
anew with blood, that the deeper crimson col-
our returns. But no one need remain in doubt
of the fact, for if the ventricle be pierced the
blood will be seen to be forcibly projected out-
wards upon each motion or pulsation when the
heart is tense.
These things, therefore, happen together or
at the same instant: the tension of the heart,
the pulse of its apex, which is felt externally by
its striking against the chest, the thickening of
its parietes, and the forcible expulsion of the
blood it contains by the constriction of its
ventricles.
Hence the very opposite of the opinions com-
monly received appears to be true; inasmuch as
it is generally believed that when the heart
strikes the breast and the pulse is felt without,
the heart is dilated in its ventricles and is filled
with blood; but the contrary of this is the fact,
and the heart, when it contracts, is emptied.
Whence the motion which is generally regarded
as the diastole of the heart, is in truth its sys-
tole. And in like manner the intrinsic motion of
the heart is not the diastole but the systole;
neither is it in the diastole that the heart grows
firm and tense, but in the systole, for then only,
when tense, is it moved and made vigorous.
Neither is it by any means to be allowed that
the heart only moves in the line of its straight
fibres, although the great Vcsalius, giving this
notion countenance, quotes a bundle of osiers
bound into a pyramidal heap in illustration;
meaning, that as the apex is approached to the
base, so are the sides made to bulge out in the
fashion of arches, the cavities to dilate, the
ventricles to acquire the form of a cupping-
glass and so to suck in the blood. But the true
effect of every one of its fibres is to const ringe
the heart at the same time that they render it
tense; and this rather with the effect of thicken-
ing and amplifying the walls and substance of
the organ than enlarging its ventricles. And,
again, as the fibres run from the apex to the
base, and draw the apex towards the base, they
do not tend to make the walls of the heart bulge
out in circles, but rather the contrary; inas-
much as every fibre that is circularly disposed,
tends to become straight when it contracts;
and is distended laterally and thickened, as in
the case of muscular fibres in general, when
they contract, that is, when they are shortened
longitudinally, as we see them in the bellies of
the muscles of the body at large. To all this let
it be added that not only are the ventricles con-
tracted in virtue of the direction and condensa-
tion of their walls, but further, that those fibres,
or bands, styled nerves by Aristotle, which are
so conspicuous in the ventricles of the larger
animals, and contain all the straight fibres (the
parietes of the heart containing only circular
ones), when they contract simultaneously, by
an admirable adjustment all the internal sur-
faces are drawn together, as if with cords, and
so is the charge of blood expelled with force.
Neither is it true, as vulgarly believed, that
the heart by any dilatation or motion of its
own, has the power of drawing the blood into
the ventricles; for when it acts and becomes
tense, the blood is expelled; when it relaxes and
sinks together it receives the blood in the man-
ner and wise which will by and by be explained.
CHAPTER 3. Of the motions of arteries, as seen in
the dissection of living animals
IN connexion with the motions of the heart
these things are further to be observed having
reference to the motions and pulses of the
arteries:
1. At the moment the heart contracts, and
when the breast is struck, when, in short, the
organ is in its state of systole, the arteries are
dilated, yield a pulse, and are in the state of
diastole. In like manner, when the right ven-
tricle contracts and propels its charge of blood,
the arterial vein is distended at the same time
with the other arteries of the body.
2. When the left ventricle ceases to act, to
contract, to pulsate, the pulse in the arteries
also ceases; further, when this ventricle con-
tracts languidly, the pulse in the arteries is
scarcely perceptible. In like manner, the pulse
in the right ventricle failing, the pulse in the
vena arteriosa ceases also.
3. Further, when an artery is divided or punc-
tured, the blood is seen to be forcibly propelled
from the wound at the moment the left ven-
tricle contracts; and, again, when the pulmo-
nary artery is wounded, the blood will be seen
spouting forth with violence at the instant
when the right ventricle contracts.
So also in fishes, if the vessel which leads from
the heart to the gills be divided, at the moment
when the heart becomes tense and contracted,
at the same moment does the blood flow with
force from the divided vessel.
In the same way, finally, when we see the
blood in arteriotomy projected now to a greater,
now to a less distance, and that the greater jet
corresponds to the diastole of the artery and
to the time when the heart contracts and strikes
the ribs, and is in its state of systole, we under-
276
WILLIAM HARVEY
stand that the blood is expelled by the same
movement.
From these facts it is manifest, in opposition
to commonly received opinions, that the dias-
tole of the arteries corresponds with the time of
the heart's systole; and that the arteries are
filled and distended by the blood forced into
them by the contraction of the ventricles; the
arteries, therefore, are distended, because they
are filled like sacs or bladders, and are not filled
because they expand like bellows. It is in virtue
of one and the same cause, therefore, that all
the arteries of the body pulsate, viz., the con-
traction of the left ventricle; in the same way
as the pulmonary artery pulsates by the con-
traction of the right ventricle.
Finally, that the pulses of the arteries are due
to the impulses of the blood from the left ven-
tricle may be illustrated by blowing into a
glove, when the whole of the fingers will be
found to become distended at one and the same
time, and in their tension to bear some resem-
blance to the pulse. For in the ratio of the ten-
sion is the pulse of the heart, fuller, stronger,
more frequent as that acts more vigorously,
still preserving the rhythm and volume, and
order of the heart's contractions. Nor is it to be
expected that because of the motion of the
blood, the time at which the contraction of the
heart takes place, and that at which the pulse
in an artery (especially a distant one) is felt,
shall be otherwise than simultaneous: it is here
the same as in blowing up a glove or bladder;
for in a plenum (as in a drum, a long piece of
timber, &c.) the stroke and the motion occur
at both extremities at the same time. Aristotle,
too, has said, "the blood of all animals palpi-
tates within their veins, (meaning the arteries)
and by the pulse is sent everywhere simultane-
ously."1 And further, "thus do all the veins
pulsate together and by successive strokes, be-
cause they all depend upon the heart; and, as it
is always in motion, so are they likewise always
moving together, but by successive move-
ments."2 It is well to observe with Galen, in
this place, that the old philosophers called the
arteries veins.
I happened upon one occasion to have a par-
ticular case under my care, which plainly satis-
fied me of this truth: a certain person was af-
fected with a large pulsating tumour on the
right side of the neck, called an aneurism, just
at that part where the artery descends into the
axilla, produced by an erosion of the artery it-
1 History of Animals, in, 19.
8 On Breathing, 20.
self, and daily increasing in size; this tumour
was visibly distended as it received the charge
of blood brought to it by the artery, with each
stroke of the heart: the connexion of parts was
obvious when the body of the patient came to
be opened after his death. The pulse in the cor-
responding arm was small, in consequence of
the greater portion of the blood being diverted
into the tumour and so intercepted.
Whence it appears that wherever the motion
of the blood through the arteries is impeded,
whether it be by compression or infarction, or
interception, there do the remote divisions of
the arteries beat less forcibly, seeing that the
pulse of the arteries is nothing more than the
impulse or shock of the blood in these vessels.
CHAPTER 4. Of the motion of the heart and its
auricles, as seen in the bodies of living animals
BESIDES the motions already spoken of, we
have still to consider those that appertain to
the auricles.
Caspar Bauhin and John Riolan,3 most learned
men and skilful anatomists, inform us from
their observations that if we carefully watch
the movements of the heart in the vivisection
of an animal, we shall perceive four motions dis-
tinct in time and in place, two of which are
proper to the auricles, two to the ventricles.
With all deference to such authority, I say that
there are four motions distinct in point of place,
but not of time; for the two auricles move to-
gether, and so also do the two ventricles, in
such wise that though the places be four, the
times are only two. And this occurs in the fol-
lowing manner:
There are, as it were, two motions going on
together; one of the auricles, another of the
ventricles; these by no means taking place si-
multaneously, but the motion of the auricles
preceding, that of the heart itself following;
the motion appearing to begin from the auri-
cles and to extend to the ventricles. When all
things are becoming languid, and the heart is
dying, as also in fishes and the colder blooded
animals, there is a short pause between these
two motions, so that the heart aroused, as it
were, appears to respond to the motion, now
more quickly, now more tardily; and at length,
and when near to death, it ceases to respond by
its proper motion, but seems, as it were, to nod
the head, and is so obscurely moved that it ap-
pears rather to give signs of motion to the pul-
sating auricle, than actually to move. The
heart, therefore, ceases to pulsate sooner than
* Bauhin, n, 21 ; Riolan, vin, i.
MOTION OF THE HEART
277
the auricles, so that the auricles have been said
to outlive it, the left ventricle ceasing to pul-
sate first of all; then its auricle, next the right
ventricle; and, finally, all the other parts being
at rest and dead, as Galen long since observed,
the right auricle still continues to beat; life,
therefore, appears to linger longest in the right
auricle. Whilst the heart is gradually dying, it
is sometimes seen to reply, after two or three
contractions of the auricles, roused as it were to
action, and making a single pulsation, slowly,
unwillingly, and with an effort.
But this especially is to be noted, that after
the heart has ceased to beat, the auricles, how-
ever, still contracting, a finger placed upon the
ventricles perceives the several pulsations of
the auricles, precisely in the same way and for
the same reason, as we have said, that the pulses
of the ventricles are felt in the arteries, to wit,
the distension produced by the jet of blood.
And if at this time, the auricles alone pulsating,
the point of the heart be cut off with a pair of
scissors, you will perceive the blood flowing out
upon each contraction of the auricles. Whence
it is manifest how the blood enters the ventri-
cles, not by any attraction or dilatation of the
heart, but thrown into them by the pulses of
the auricles.
And here I would observe, that whenever I
speak of pulsations as occurring in the auricles
or ventricles, I mean contractions: first the au-
ricles contract, and then and subsequently the
heart itself contracts. When the auricles contract
they are seen to become whiter, especially
where they contain but little blood; but they
are filled as magazines or reservoirs of the blood,
which is tending spontaneously and, by the
motion of the veins, under pressure towards
the centre; the whiteness indicated is most con-
spicuous towards the extremities or edges of the
auricles at the time of their contractions.
In fishes and frogs, and other animals which
have hearts with but a single ventricle, and for
an auricle have a kind of bladder much dis-
tended with blood, at the base of the organ, you
may very plainly perceive this bladder con-
tracting first, and the contraction of the heart
or ventricle following afterwards.
But I think it right to describe what I have
observed of an opposite character: the heart of
an eel, of several fishes, and even of some ani-
mals taken out of the body, beats without auri-
cles; nay, if it be cut in pieces the several parts
may still be seen contracting and relaxing; so
that in these creatures the body of the heart
may be seen pulsating, palpitating, after the
cessation of all motion in the auricle. But is not
this perchance peculiar to animals more tena-
cious of life, whose radical moisture is more glu-
tinous, or fat and sluggish, and less readily sol-
uble? The same faculty indeed appears in the
flesh of eels, generally, which even when skin-
ned and embowelled, and cut into pieces, are
still seen to move.
Experimenting with a pigeon upon one oc-
casion, after the heart had wholly ceased to pul-
sate, and the auricles too had become motion-
less, I kept my finger wetted with saliva and
warm for a short time upon the heart, and ob-
served that under the influence of this fomen-
tation it recovered new strength and life, so
that both ventricles and auricles pulsated, con-
tracting and relaxing alternately, recalled as it
were from death to life.
Besides this, however, I have occasionally ob-
served, after the heart and even its right auri-
cle had ceased pulsating, when it was in articulo
mortis in short, that an obscure motion, an un-
dulation or palpitation, remained in the blood
itself, which was contained in the right auricle,
this being apparent so long as it was inbued
with heat and spirit. And indeed a circum-
stance of the same kind is extremely manifest
in the course of the generation of animals, as
may be seen in the course of the first seven days
of the incubation of the chick: a drop of blood
makes its appearance which palpitates, as Aris-
totle had already observed; from this, when the
growth is further advanced and the chick is
fashioned, the auricles of the heart are formed,
which pulsating henceforth give constant signs
of life. When at length, and after the lapse of a
few days, the outline of the body begins to be
distinguished, then is the ventricular part of
the heart also produced; but it continues for a
time white and apparently bloodless, like the
rest of the animal; neither does it pulsate or
give signs of motion. I have seen a similar con-
dition of the heart in the human foetus about
the beginning of the third month, the heart
being then whitish and bloodless, although its
auricles contained a considerable quantity of
purple blood. In the same way in the egg,
when the chick was formed and had increased
in size, the heart too increased and acquired
ventricles, which then began to receive and to
transmit blood.
And this leads me to remark that he who in-
quires very particularly into this matter will
not conclude that the heart, as a whole, is the
primum vivens^ ultimum moriens — the first part
to live, the last to die, but rather its auricles, or
278
WILLIAM HARVEY
the part which corresponds to the auricles in
serpents, fishes, &c., which both lives before the
heart and dies after it.
Nay, has not the blood itself or spirit an ob-
scure palpitation inherent in it, which it has
even appeared to me to retain after death ? And
it seems very questionable whether or not we
are to say that life begins with the palpitation
or beating of the heart. The seminal fluid of all
animals — the prolific spirit, as Aristotle ob-
served, leaves their body with a bound and like
a living thing; and nature in death, as Aristotle1
further remarks, retracing her steps, reverts to
whence she had set out, returns at the end of
her course to the goal whence she had started;
and as animal generation proceeds from that
which is not animal, entity from non-entity, so,
by a retrograde course, entity, by corruption,
is resolved into non-entity; whence that in ani-
mals, which was last created, fails first; and that
which was first, fails last.
I have also observed that almost all animals
have truly a heart, not the larger creatures
only, and those that have red blood, but the
smaller, and bloodless ones also, such as slugs,
snails, scallops, shrimps, crabs, crayfish, and
many others; nay, even in wasps, hornets and
flies, I have, with the aid of a magnifying glass,
and at the upper part of what is called the tail,
both seen the heart pulsating myself, and
shown it to many others.
But in the exsanguine tribes the heart pul-
sates sluggishly and deliberately, contracting
slowly as in animals that are moribund, a fact
that may readily be seen in the snail, whose
heart will be found at the bottom of that orifice
in the right side of the body which is seen to be
opened and shut in the course of respiration,
and whence saliva is discharged, the incision
being made in the upper aspect of the body,
near the part which corresponds to the liver.
This, however, is to be observed: that in win-
ter and the colder season, exsanguine animals,
such as the snail, show no pulsations; they seem
rather to live after the manner of vegetables, or
of those other productions which are therefore
designated plant-animals.
It is also to be noted that all animals which
have a heart, have also auricles, or something
analogous to auricles; and further, that wher-
ever the heart has a double ventricle there are
always two auricles present, but not otherwise.
If you turn to the production of the chick in
ovo, however, you will find at first no more
than a vesicle or auricle, or pulsating drop of
1 On the Motion ofAntmak, 8.
blood; it is only by and by, when the develop-
ment has made some progress, that the heart is
fashioned: even so in certain animals not des-
tined to attain to the highest perfection in their
organization, such as bees, wasps, snails, shrimps,
crayfish, &c., we only find a certain pulsating
vesicle, like a sort of red or white palpitating
point, as the beginning or principle of their life.
We have a small shrimp in these countries,
which is taken in the Thames and in the sea,
the whole of whose body is transparent; this
creature, placed in a little water, has frequently
afforded myself and particular friends an op-
portunity of observing the motions of the
heart with the greatest distinctness, the exter-
nal parts of the body presenting no obstacle to
our view, but the heart being perceived as
though it had been seen through a window.
I have also observed the first rudiments of
the chick in the course of the fourth or fifth day
of the incubation, in the guise of a little cloud,
the shell having been removed and the egg im-
mersed in clear tepid water. In the midst of the
cloudlet in question there was a bloody point so
small that it disappeared during the contrac-
tion and escaped the sight, but in the relaxation
it reappeared again, red and like the point of a
pin; so that betwixt the visible and invisible,
betwixt being and not being, as it were, it gave
by its pulses a kind of representation of the
commencement of life.
CHAPTER 5. Of the motion, action, and office of the
heart
FROM these and other observations of the like
kind, I am persuaded it will be found that the
motion of the heart is as follows :
First of all, the auricle contracts, and in the
course of its contraction throws the blood
(which it contains in ample quantity as the
head of the veins, the storehouse and cistern of
the blood) into the ventricle, which being
filled, the heart raises itself straightway, makes
all its fibres tense, contracts the ventricles, and
performs a beat, by which beat it immediately
sends the blood supplied to it by the auricle in-
to the arteries; the right ventricle sending its
charge into the lungs by the vessel which is
called vena arteriosa, but which, in structure
and function, and all things else, is an artery;
the left ventricle sending its charge into the
aorta, and through this by the arteries to the
body at large.
These two motions, one of the ventricles,
another of the auricles, take place consecutive-
ly, but in such a manner that there is a kind of
MOTION OF THE HEART
279
harmony or rhythm preserved between them,
the two concurring in such wise that but one
motion is apparent, especially in the warmer
blooded animals, in which the movements in
question are rapid. Nor is this for any other
reason than it is in a piece of machinery, in
which, though one wheel gives motion to an-
other, yet all the wheels seem to move simul-
taneously; or in that mechanical contrivance
which is adapted to firearms, where the trigger
being touched, down comes the flint, strikes
against the steel, elicits a spark, which falling
among the powder, it is ignited, upon which
the flame extends, enters the barrel, causes the
explosion, propels the ball, and the mark is at-
tained— all of which incidents, by reason of the
celerity with which they happen, seem to take
place in the twinkling of an eye. So also in de-
glutition: by the elevation of the root of the
tongue, and the compression of the mouth, the
food or drink is pushed into the fauces, the lar-
ynx is closed by its own muscles, and the epi-
glottis, whilst the pharynx, raised and opened
by its muscles no otherwise than is a sac that is
to be filled, is lifted up, and its mouth dilated;
upon which, the mouthful being received, it is
forced downwards by the transverse muscles,
and then carried farther by the longitudinal
ones. Yet are all these motions, though executed
by different and distinct organs, performed
harmoniously, and in such order, that they
seem to constitute but a single motion and act,
which we call deglutition.
Even so does it come to pass with the motions
and action of the heart, which constitute a kind
of deglutition, a transfusion of the blood from
the veins to the arteries. And if anyone, bear-
ing these things in mind, will carefully watch
the motions of the heart in the body of a living
animal, he will perceive not only all the partic-
ulars I have mentioned, viz., the heart becom-
ing erect, and making one continuous motion
with its auricles; but further, a certain obscure
undulation and lateral inclination in the direc-
tion of the axis of the right ventricle, twisting
itself slightly in performing its work. And in-
deed everyone may see when a horse drinks
that the water is drawn in and transmitted
to the stomach at each movement of the
throat, the motion being accompanied with
a sound, and yielding a pulse both to the
ear and the touch; in the same way it is with
each motion of the heart, when there is the de-
livery of a quantity of blood from the veins to
the arteries, that a pulse takes place, and can be
heard within the chest.
The motion of the heart, then, is entirely of
this description, and the one action of the heart
is the transmission of the blood and its distri-
bution, by means of the arteries, to the very
extremities of the body; so that the pulse
which we feel in the arteries is nothing more
than the impulse of the blood derived from the
heart.
Whether or not the heart, besides propelling
the blood, giving it motion locally, and distrib-
uting it to the body, adds anything else to it —
heat, spirit, perfection — must be inquired into
by and by, and decided upon other grounds. So
much may suffice at this time, when it is shown
that by the action of the heart the blood is
transfused through the ventricles from the
veins to the arteries, and distributed by them
to all parts of the body.
So much, indeed, is admitted by all, both
from the structure of the heart and the arrange-
ment and action of its valves. But still they are
like persons purblind or groping about in the
dark; and then they give utterance to diverse,
contradictory, and incoherent sentiments, de-
livering many things upon conjecture, as we
have already had occasion to remark.
The grand cause of hesitation and error in
this subject appears to me to have been the in-
timate connexion between the heart and the
lungs. When men saw both the vena arteriosa
and the arteriae venosae losing themselves in the
lungs, of course, it became a puzzle to them to
know how or by what means the right ventricle
should distribute the blood to the body, or the
left draw it from the venae cavae. This fact is
borne witness to by Galen, whose words, when
writing against Erasistratus in regard to the ori-
gin and use of the veins and the coction of the
blood, are the following: "You will reply," he
says, "that the effect is so; that the blood is pre-
pared in the liver, and is thence transferred to
the heart to receive its proper form and last
perfection; a statement which does not appear
devoid of reason; for no great and perfect work
is ever accomplished at a single effort, or re-
ceives its final polish from one instrument. But
if this be actually so, then show us another ves-
sel which draws the absolutely perfect blood
from the heart, and distributes it as the arteries
do the spirits over the whole body."1 Here then
is a reasonable opinion not allowed, because,
forsooth, besides not seeing the true means of
transit, he could not discover the vessel which
should transmit the blood from the heart to
the body at large!
1 DC placitis Htppocratis ct Platonis, vi.
280
WILLIAM HARVEY
But had anyone been there in behalf of Era-
sistratus, and of that opinion which we now es-
pouse, and which Galen himself acknowledges
in other respects consonant with reason, to have
pointed to the aorta as the vessel which distrib-
utes the blood from the heart to the rest of the
body, I wonder what would have been the an-
swer of that most ingenious and learned man ?
Had he said that the artery transmits spirits
and not blood, he would indeed sufficiently
have answered Erasistratus, who imagined that
the arteries contained nothing but spirits; but
then he would have contradicted himself, and
given a foul denial to that for which he had
keenly contended in his writings against this
very Erasistratus, to wit, that blood in sub-
stance is contained in the arteries, and not
spirits; a fact which he demonstrated not only
by many powerful arguments, but by experi-
ments.
But if the divine Galen will here allow, as in
other places he does, "that all the arteries of
the body arise from the great artery, and that
this takes its origin from the heart; that all
these vessels naturally contain and carry blood ;
that the three semilunar valves situated at the
orifice of the aorta prevent the return of the
blood into the heart, and that nature never
connected them with this, the most noble vis-
cus of the body, unless for some most impor-
tant end"; if, I say, this father of physic admits
all these things — and I quote his own words— I
do not see how he can deny that the great ar-
tery is the very vessel to carry the blood, when
it has attained its highest term of perfection,
from the heart for distribution to all parts of
the body. Or would he perchance still hesitate,
like all who have come after him, even to the
present hour, because he did not perceive the
route by which the blood was transferred from
the veins to the arteries, in consequence, as I
have already said, of the intimate connexion
between the heart and the lungs ? And that this
difficulty puzzled anatomists not a little, when
in their dissections they found the pulmonary
artery and left ventricle full of thick, black, and
clotted blood, plainly appears, when they felt
themselves compelled to affirm that the blood
made its way from the right to the left ventricle
by sweating through the septum of the heart.
But this fancy I have already refuted. A new
pathway for the blood must therefore be pre-
pared and thrown open, and being once ex-
posed, no further difficulty will, I believe, be
experienced by anyone in admitting what I
have already proposed in regard to the pulse of
the heart and arteries, viz., the passage of the
blood from the veins to the arteries, and its
distribution to the whole of the body by means
of these vessels.
CHAPTER 6. Of the course by which the blood is
carried from the vena cava into the arteries^ or from
the right into the left ventricle of the heart
SINCE the intimate connexion of the heart with
the lungs, which is apparent in the human sub-
ject, has been the probable cause of the errors
that have been committed on this point, they
plainly do amiss who, pretending to speak of
the parts of animals generally, as anatomists for
the most part do, confine their researches to
the human body alone, and that when it is
dead. They obviously act no otherwise than he
who, having studied the forms of a single com-
monwealth, should set about the composition
of a general system of polity; or who, having
taken cognizance of the nature of a single field,
should imagine that he had mastered the
science of agriculture; or who, upon the ground
of one particular proposition, should proceed to
draw general conclusions.
Had anatomists only been as conversant with
the dissection of the lower animals as they are
with that of the human body, the matters that
have hitherto kept them m a perplexity of
doubt would, in my opinion, have met them
freed from every kind of difficulty.
And, first, in fishes, in which the heart con-
sists of but a single ventricle, they having no
lungs, the thing is sufficiently manifest. Here
the sac, which is situated at the base of the
heart, and is the part analogous to the auricle in
man, plainly throws the blood into the heart,
and the heart, in its turn, conspicuously trans-
mits it by a pipe or artery, or vessel analogous
to an artery; these are facts which are con-
firmed by simple ocular inspection, as well as
by a division of the vessel, when the blood is
seen to be projected by each pulsation of the
heart.
The same thing is also not difficult of demon-
stration in those animals that have either no
more, or, as it were, no more than a single ven-
tricle to the heart, such as toads, frogs, serpents,
and lizards, which, although they have lungs in
a certain sense, as they have a voice (and I have
many observations by me on the admirable
structure of the lungs of these animals, and
matters appertaining, which, however, I can-
not introduce in this place), still their anatomy
plainly shows that the blood is transferred in
them from the veins to the arteries in the same
MOTION OF THE HEART
281
manner as in higher animals, viz., by the ac-
tion of the heart; the way, in fact, is patent,
open, manifest; there is no difficulty, no room
for hesitating about it; for in them the matter
stands precisely as it would in man, were the
septum of his heart perforated or removed, or
one ventricle made out of two; and this being
the case, I imagine that no one will doubt as
to the way by which the blood may pass from
the veins into the arteries.
But as there are actually more animals which
have no lungs than there are which be furnished
with them, and in like manner a greater num-
ber which have only one ventricle than there
are which have two, it is open to us to conclude,
judging from the mass or multitude of living
creatures, that for the major part, and gener-
ally, there is an open way by which the blood is
transmitted from the veins through the sinuses
or cavities of the heart into the arteries.
I have, however, cogitating with myself, seen
further, that the same thing obtained most ob-
viously in the embryos of those animals that
have lungs; for in the fcetus the four vessels be-
longing to the heart, viz., the vena cava, the
vena arteriosa or pulmonary artery, the arteria
venalis or pulmonary vein, and the arteria mag-
na or aorta, are all connected otherwise than in
the adult; a fact sufficiently known to every
anatomist. The first contact and union of the
vena cava with the arteria venosa or pulmo-
nary veins, which occurs before the cava opens
properly into the right ventricle of the heart,
or gives off the coronary vein, a little above its
escape from the liver, is by a lateral anastomo-
sis; this is an ample foramen, of an oval form,
communicating between the cava and the ar-
teria venosa, or pulmonary vein, so that the
blood is free to flow in the greatest abundance
by that foramen from the vena cava into the
arteria venosa or pulmonary vein, and left auri-
cle, and from thence into the left ventricle; and
further, in this foramen ovale, from that part
which regards the arteria venosa, or pulmonary
vein, there is a thin tough membrane, larger
than the opening, extended like an operculum
or cover; this membrane in the adult blocking
up the foramen, and adhering on all sides, fi-
nally closes it up, and almost obliterates every
trace of it. This membrane, however, is so con-
trived in the fcetus, that falling loosely upon it-
self, it permits a ready access to the lungs and
heart, yielding a passage to the blood which is
streaming from the cava, and hindering the
tide at the same time from flowing back into
that vein. All things, in short, permit us to be-
lieve that in the embryo the blood must con-
stantly pass by this foramen from the vena cava
into the arteria venosa, or pulmonary vein, and
from thence into the left auricle of the heart;
and having once entered there, it can never re-
gurgitate.
Another union is that by the vena arteriosa,
or pulmonary artery, and is effected when that
vessel divides into two branches after its escape
from the right ventricle of the heart. It is as if
to the two trunks already mentioned a third
were superadded, a kind of arterial canal, car-
ried obliquely from the vena arteriosa, or pul-
monary artery, to perforate and terminate in
the arteria magna or aorta. In the embryo, con-
sequently, there are, as it were, two aortas, or
two roots of the arteria magna, springing from
the heart. This canalis arteriosus shrinks grad-
ually after birth, and is at length and finally
almost entirely withered, and removed, like
the umbilical vessels.
The canalis arteriosus contains no membrane
or valve to direct or impede the flow of the
blood in this or in that direction: for at the root
of the vena arteriosa, or pulmonary artery, of
which the canalis arteriosus is the continuation
in the foetus, there are three sigmoid or semi-
lunar valves, which open from within outwards,
and oppose no obstacle to the blood flowing in
this direction or from the right ventricle into
the pulmonary artery and aorta; but they pre-
vent all regurgitation from the aorta or pul-
monic vessels back upon the right ventricle;
closing with perfect accuracy, they oppose an
effectual obstacle to everything of the kind in
the embryo. So that there is also reason to be-
lieve that when the heart contracts, the blood
is regularly propelled by the canal or passage
indicated from the right ventricle into the
aorta.
What is commonly said in regard to these
two great communications, to wit, that they
exist for the nutrition of the lungs, is both im-
probable and inconsistent; seeing that in the
adult they are closed up, abolished, and con-
solidated, although the lungs, by reason of their
heat and motion, must then be presumed to re-
quire a larger supply of nourishment. The same
may be said in regard to the assertion that the
heart in the embryo does not pulsate, that it
neither acts nor moves, so that nature was forced
to make these communications for the nutri-
tion of the lungs. This is plainly false; for simple
inspection of the incubated egg, and of embryos
just taken out of the uterus, shows that the
heart moves precisely in them as in adults, and
282
WILLIAM HARVEY
that nature feels no such necessity. I have my-
self repeatedly seen these motions, and Aristotle
is likewise witness of their reality. "The pulse,"
he observes, "inheres in the very constitution
of the heart, and appears from the beginning,
as is learned both from the dissection of living
animals, and the formation of the chick in the
egg.'*1 But we further observe that the passages
in question are not only pervious up to the pe-
riod of birth in man, as well as in other animals,
as anatomists in general have described them,
but for several months subsequently, in some
indeed for several years, not to say for the whole
course of life; as, for example, in the goose,
snipe, and various birds, and many of the smaller
animals. And this circumstance it was, perhaps,
that imposed upon Botallus, who thought he
had discovered a new passage for the blood
from the vena cava into the left ventricle of the
heart; and I own that when I met with the same
arrangement in one of the larger members of
the mouse family, in the adult state, I was my-
self at first led to something of a like conclusion.
From this it will be understood that in the
human embryo, and in the embryos of animals
in which the communications are not closed,
the same thing happens, namely, that the heart
by its motion propels the blood by obvious and
open passages from the vena cava into the aorta
through the cavities of both the ventricles; the
right one receiving the blood from the auricle,
and propelling it by the vena arteriosa, or pul-
monary artery, and its continuation, named the
ductus arteriosus, into the aorta; the left, in
like manner, charged by the contraction of its
auricle, which has received its supply through
the foramen ovale from the vena cava, con-
tracting, and projecting the blood through the
root of the aorta into the trunk of that vessel.
In embryos, consequently, whilst the lungs
are yet in a state of inaction, performing no
function, subject to no motion any more than
if they had not been present, nature uses the
two ventricles of the heart as if they formed but
one, for the transmission of the blood. The con-
dition of the embryos of those animals which
have lungs, whilst these organs are yet in abey-
ance and not employed, is the same as that of
those animals which have no lungs.
So clearly, therefore, does it appear in the
case of the foetus, viz., that the heart by its ac-
tion transfers the blood from the vena cava into
the aorta, and that by a route as obvious and
open, as if in the adult the two ventricles were
made to communicate by the removal of their
1 De sptritu, 5 [a pseudo-Aristotelian work].
septum. Since, then, we find that in the greater
number of animals, in all, indeed, at a certain
period of their existence, the channels for the
transmission of the blood through the heart are
so conspicuous, we have still to inquire where-
fore in some creatures — those, namely, that
have warm blood, and that have attained to the
adult age, man among the number— we should
not conclude that the same thing is accom-
plished through the substance of the lungs,
which in the embryo, and at a time when the
function of these organs is in abeyance, nature
effects by the direct passages described, and
which, indeed, she seems compelled to adopt
through want of a passage by the lungs; or
wherefore it should be better (for nature always
does that which is best) that she should close up
the various open routes which she had formerly
made use of in the embryo and foetus, and still
uses in all other animals; not only opening up
no new apparent channels for the passage of the
blood, therefore, but even entirely shutting up
those which formerly existed.
And now the discussion is brought to this
point, that they who inquire into the ways by
which the blood reaches the left ventricle of the
heart and pulmonary veins from the vena cava,
will pursue the wisest course if they seek by dis-
section to discover the causes why in the larger
and more perfect animals of mature age, nature
has rather chosen to make the blood percolate
the parenchyma of the lungs, than as in other
instances chosen a direct and obvious course —
for I assume that no other path or mode of
transit can be entertained. It must be either be-
cause the larger and more perfect animals are
warmer, and when adult their heat greater —
ignited, as I might say, and requiring to be
damped or mitigated; therefore it may be that
the blood is sent through the lungs, that it may
be tempered by the air that is inspired, and
prevented from boiling up, and so becoming
extinguished, or something else of the sort. But
to determine these matters, and explain them
satisfactorily, were to enter on a speculation in
regard to the office of the lungs and the ends
for which they exist; and upon such a subject,
as well as upon what pertains to eventilation, to
the necessity and use of the air, &c., as also to
the variety and diversity of organs that exist in
the bodies of animals in connexion with these
matters, although I have made a vast number
of observations, still, lest I should be held as
wandering too wide of my present purpose,
which is the use and motion of the heart, and
be charged with speaking of things beside the
MOTION OF THE HEART
283
question, and rather complicating and quitting
than illustrating it, I shall leave such topics till
I can more conveniently set them forth in a
treatise apart. And now, returning to my im-
mediate subject, I go on with what yet remains
for demonstration, viz., that in the more per-
fect and warmer adult animals, and man, the
blood passes from the right ventricle of the
heart by the vena arteriosa, or pulmonary ar-
tery, into the lungs, and thence by the arteriae
venosae, or pulmonary veins, into the left auri-
cle, and thence into the left ventricle of the
heart. And, first, I shall show that this may be
so, and then I shall prove that it is so in fact.
CHAPTER 7. The blood percolates the substance of
the lungs from the right ventricle of the heart into
the pulmonary veins and left ventricle
THAT this is possible, and that there is nothing
to prevent it from being so, appears when we
reflect on the way in which water percolating
the earth produces springs and rivulets, or when
we speculate on the means by which the sweat
passes through the skin, or the urine through
the parenchyma of the kidneys. It is well
known that persons who use the Spa waters, or
those of La Madonna, in the territories of Padua,
or others of an acidulous or vitriolated nature,
or who simply swallow drinks by the gallon,
pass all off again within an hour or two by urine.
Such a quantity of liquid must take some short
time in the concoction: it must pass through
the liver (it is allowed by all that the juices of
the food we consume pass twice through this
organ in the course of the day); it must flow
through the veins, through the parenchyma of
the kidneys, and through the ureters into the
bladder.
To those, therefore, whom I hear denying
that the blood, aye the whole mass of the blood
may pass through the substance of the lungs,
even as the nutritive juices percolate the liver,
asserting such a proposition to be impossible,
and by no means to be entertained as credible,
I reply, with the poet, that they are of that race
of men who, when they will, assent full readily,
and when they will not, by no manner of means;
who, when their assent is wanted, fear, and
when it is not, fear not to give it.
The parenchyma of the liver is extremely
dense, so is that of the kidney; the lungs, again,
are of a much looser texture, and if compared
with the kidneys are absolutely spongy. In the
liver there is no forcing, no impelling power; in
the lungs the blood is forced on by the pulse of
the right ventricle, the necessary effect of whose
impulse is the distension of the vessels and pores
of the lungs. And then the lungs, in respiration,
are perpetually rising and falling; motions, the
effect of which must needs be to open and shut
the pores and vessels, precisely as in the case of
a sponge, and of parts having a spongy structure,
when they are alternately compressed and again
are suffered to expand. The liver, on the con-
trary, remains at rest, and is never seen to be
dilated and constricted. Lastly, if no one denies
the possibility of the whole of the ingested juices
passing through the liver, in man, oxen, and the
larger animals generally, in order to reach the
vena cava, and for this reason, that if nourish-
ment is to go on, these juices must needs get
into the veins, and there is no other way but
the one indicated, why should not the same
arguments be held of avail for the passage of
the blood in adults through the lungs? Why
not, with Columbus, that skilful and learned
anatomist, maintain and believe the like, from
the capacity and structure of the pulmonary
vessels; from the fact of the pulmonary veins
and ventricle corresponding with them, being
always found to contain blood, which must
needs have come from the veins, and by no
other passage save through the lungs? Colum-
bus, and we also, from what precedes, from dis-
sections, and other arguments, conceive the
thing to be clear. But as there are some who
admit nothing unless upon authority, let them
learn that the truth I am contending for can be
confirmed from Galen's own words, namely,
that not only may the blood be transmitted
from the pulmonary artery into the pulmonary
veins, then into the left ventricle of the heart,
and from thence into the arteries of the body,
but that this is effected by the ceaseless pulsa-
tion of the heart and the motion of the lungs
in breathing.
There are, as everyone knows, three sigmoid
or semilunar valves situated at the orifice of the
pulmonary artery, which effectually prevent
the blood sent into the vessel from returning in-
to the cavity of the heart. Now Galen, explain-
ing the uses of these valves, and the necessity
for them, employs the following language:
"There is everywhere a mutual anastomosis and
inosculation of the arteries with the veins, and
they severally transmit both blood and spirit,
by certain invisible and undoubtedly very nar-
row passages. Now if the mouth of the vena
arteriosa, or pulmonary artery, had stood in
like manner continually open, and nature had
found no contrivance for closing it when requi-
site, and opening it again, it would have been
284
WILLIAM HARVEY
impossible that the blood could ever have passed
by the invisible and delicate mouths, during
the contractions of the thorax, into the arteries;
for all things are not alike readily attracted or
repelled; but that which is light is more readily
drawn in, the instrument being dilated, and
forced out again when it is contracted, than
that which is heavy; and in like manner is any-
thing drawn more rapidly along an ample con-
duit, and again driven forth, than it is through
a narrow tube. But when the thorax is con-
tracted, the pulmonary veins, which are in the
lungs, being driven inwardly, and powerfully
compressed on every side, immediately force
out some of the spirit they contain, and at the
same time assume a certain portion of blood by
those subtile mouths; a thing that could never
come to pass were the blood at liberty to flow
back into the heart through the great orifice of
the pulmonary artery. But its return through
this great opening being prevented, when it is
compressed on every side, a certain portion of
it distils into the pulmonary veins by the mi-
nute orifices mentioned."1 And shortly after-
wards, in the very next chapter, he says: "The
more the thorax contracts, the more it strives
to force out the blood, the more exactly do
these membranes (viz., the sigmoid valves)
close up the mouth of the vessel, and suffer
nothing to regurgitate." The same fact he has
also alluded to in a preceding part of the tenth
chapter: "Were there no valves, a three-fold
inconvenience would result, so that the blood
would then perform this lengthened course in
vain; it would flow inwards during the diastoles
of the lungs, and fill all their arteries; but in the
systoles, in the manner of the tide, it would
ever and anon, like the Euripus, flow back-
wards and forwards by the same way, with a
reciprocating motion, which would nowise suit
the blood. This, however, may seem a matter
of little moment; but if it meantime appear
that the function of respiration suffer, then I
think it would be looked upon as no trifle/' &c.
And again, and shortly afterwards: "And then a
third inconvenience, by no means to be thought
lightly of, would follow, were the blood moved
backwards during the expirations, had not our
Maker instituted those supplementary mem-
branes." Whence, in the eleventh chapter, he
concludes: "That they have all a common use
(to wit, the valves), and that it is to prevent
regurgitation or backward motion; each, how-
ever, having a proper function, the one set
drawing matters from the heart, and prevent-
1 De usu partium, vi. 10.
ing their return, the other drawing matters in-
to the heart, and preventing their escape from
it. For nature never intended to distress the
heart with needless labour, neither to bring
aught into the organ which it had been better
to have kept away, nor to take from it again
aught which it was requisite should be brought.
Since, then, there are four orifices in all, two
in either ventricle, one of these induces, the
other educes.*' And again he says: "Further,
since there is one vessel, consisting of a simple
tunic, implanted in the heart, and another,
having a double tunic, extending from it (Galen
is here speaking of the right side of the heart,
but I extend his observations to the left side
also), a kind of reservoir had to be provided, to
which both belonging, the blood should be
drawn in by the one, and sent out by the other."
This argument Galen adduces for the transit
of the blood by the right ventricle from the
vena cava into the lungs; but we can use it with
still greater propriety, merely changing the
terms, for the passage of the blood from the
veins through the heart into the arteries. From
Galen, however, that great man, that father of
physicians, it clearly appears that the blood
passes through the lungs from the pulmonary
artery into the minute branches of the pulmo-
nary veins, urged to this both by the pulses of
the heart and by the motions of the lungs and
thorax; that the heart, moreover, is incessantly
receiving and expelling the blood by and from
its ventricles, as from a magazine or cistern, and
for this end is furnished with four sets of valves,
two serving for the induction and two for the
eduction of the blood, lest, like the Euripus,
it should be incommodiously sent hither and
thither, or flow back into the cavity which it
should have quitted, or quit the part where its
presence was required, and so the heart be
oppressed with labour in vain, and the office
of the lungs be interfered with.2 Finally, our
position that the blood is continually passing
from the right to the left ventricle, from the
vena cava into the aorta, through the porous
structure of the lungs, plainly appears from
this, that since the blood is incessantly sent
from the right ventricle into the lungs by the
pulmonary artery, and in like manner is inces-
santly drawn from the lungs into the left ven-
tricle, as appears from what precedes and the
position of the valves, it cannot do otherwise
than pass through continuously. And then, as
* See the commentary of the learned Hofmann upon
the Sixth Book of Galen, De usu partium, a work which
I first saw after I had written what precedes.
MOTION OF THE HEART
285
the blood is incessantly flowing into the right
ventricle of the heart, and is continually passed
out from the left, as appears in like manner,
and as is obvious both to sense and reason, it is
impossible that the blood can do otherwise
than pass continually from the vena cava into
the aorta.
Dissection consequently shows distinctly
what takes place in the greater number of ani-
mals, and indeed in all, up to the period of their
[foetal] maturity; and that the same thing occurs
in adults is equally certain, both from Galen's
words, and what has already been said on the
subject, only that in the former the transit is
effected by open and obvious passages, in the
latter by the obscure porosities of the lungs and
the minute inosculations of vessels. Whence it
appears that, although one ventricle of the
heart, the left to wit, would suffice for the dis-
tribution of the blood over the body, and its
eduction from the vena cava, as indeed is done
in those creatures that have no lungs, nature,
nevertheless, when she ordained that the same
blood should also percolate the lungs, saw her-
self obliged to add another ventricle, the right,
the pulse of which should force the blood from
the vena cava through the lungs into the cavity
of the left ventricle. In this way, therefore, it
may be said that the right ventricle is made for
the sake of the lungs, and for the transmission
of the blood through them, not for their nutri-
tion; seeing it were unreasonable to suppose
that the lungs required any so much more copi-
ous a supply of nutriment, and that of so much
purer and more spirituous a kind, as coming
immediately from the ventricle of the heart,
than either the brain with its peculiarly pure
substance, or the eyes with their lustrous and
truly admirable structure, or the flesh of the
heart itself, which is more commodiously nour-
ished by the coronary artery.
CHAPTER 8. Of the quantity of blood passing
through the heart from the veins to the arteries; and
of the circular motion of the blood
THUS far I have spoken of the passage of the
blood from the veins into the arteries, and of the
manner in which it is transmitted and distribut-
ed by the action of the heart; points to which
some, moved either by the authority of Galen
or Columbus, or the reasonings of others, will
give in their adhesion. But what remains to be
said upon the quantity and source of the blood
which thus passes is of so novel and unheard-of
character, that I not only fear injury to myself
from the envy of a few, but I tremble lest I have
mankind at large for my enemies, so much doth
wont and custom, that become as another na-
ture, and doctrine once sown and that hath
struck deep root, and respect for antiquity in-
fluence all men: still the die is cast, and my trust
is in my love of truth, and the candour that in-
heres in cultivated minds. And sooth to say,
when I surveyed my mass of evidence, whether
derived from vivisections, and my various re-
flections on them, or from the ventricles of the
heart and the vessels that enter into and issue
from them, the symmetry and size of these con-
duits—for nature doing nothing in vain, would
never have given them so large a relative size
without a purpose — or from the arrangement
and intimate structure of the valves in particu-
lar, and of the other parts of the heart in gen-
eral, with many things besides, I frequently
and seriously bethought me, and long revolved
in my mind, what might be the quantity of
blood which was transmitted, in how short a
time its passage might be effected, and the like;
and not finding it possible that this could be
supplied by the juices of the ingested aliment
without the veins on the one hand becoming
drained, and the arteries on the other getting
ruptured through the excessive charge of blood,
unless the blood should somehow find its way
from the arteries into the veins, and so return
to the right side of the heart; I began to think
whether there might not be a MOTION, AS IT
WERE, IN A CIRCLE. Now this I afterwards
found to be true; and I finally saw that the
blood, forced by the action of the left ventricle
into the arteries, was distributed to the body at
large, and its several parts, in the same manner
as it is sent through the lungs, impelled by the
right ventricle into the pulmonary artery, and
that it then passed through the veins and along
the vena cava, and so round to the left ventricle
in the manner already indicated. Which motion
we may be allowed to call circular, in the same
way as Aristotle says that the air and the rain
emulate the circular motion of the superior
bodies; for the moist earth, warmed by the sun,
evaporates; the vapours drawn upwards are
condensed, and descending in the form of rain,
moisten the earth again; and by this arrange-
ment are generations of living things produced;
and in like manner too are tempests and meteors
engendered by the circular motion, and by the
approach and recession of the sun.
And so, in all likelihood, does it come to pass
in the body, through the motion of the blood;
the various parts are nourished, cherished,
quickened by the warmer, more perfect, va-
286
WILLIAM HARVEY
porous, spirituous, and, as I may say, alimen-
tive blood; which, on the contrary, in contact
with these parts becomes cooled, coagulated,
and, so to speak, effete; whence it returns to
its sovereign the heart, as if to its source, or to
the inmost home of the body, there to recover
its state of excellence or perfection. Here it re-
sumes its due fluidity and receives an infusion
of natural heat— powerful, fervid, a kind of
treasury of life, and is impregnated with spirits,
and it might be said with balsam; and thence it
is again dispersed; and all this depends on the
motion and action of the heart.
The heart, consequently, is the beginning of
life; the sun of the microcosm, even as the sun
in his turn might well be designated the heart
of the world; for it is the heart by whose virtue
and pulse the blood is moved, perfected, made
apt to nourish, and is preserved from corrup-
tion and coagulation ; it is the household divin-
ity which, discharging its function, nourishes,
cherishes, quickens the whole body, and is in-
deed the foundation of life, the source of all ac-
tion. But of these things we shall speak more
opportunely when we come to speculate upon
the final cause of this motion of the heart.
Hence, since the veins are the conduits and
vessels that transport the blood, they are of two
kinds, the cava and the aorta; and this not by
reason of there being two sides of the body, as
Aristotle has it, but because of the difference
of office; nor yet, as is commonly said, in con-
sequence of any diversity of structure, for in
many animals, as I have said, the vein does not
differ from the artery in the thickness of its
tunics, but solely in virtue of their several) des-
tinies and uses. A vein and an artery, both
styled vein by the ancients, and that not unde-
servedly, as Galen has remarked, because the
one, the artery, to wit, is the vessel which car-
ries the blood from the heart to the body at
large, the other or vein of the present day
bringing it back from the general system to the
heart; the former is the conduit from, the lat-
ter the channel to, the heart; the latter con-
tains the cruder, effete blood, rendered unfit
for nutrition; the former transmits the digested,
perfect, peculiarly nutritive fluid.
CHAPTER 9. That there is a circulation of the blood
is confirmed from the first proposition
BUT lest any one should say that we give them
words only, and make mere specious assertions
without any foundation, and desire to innovate
without sufficient cause, three points present
themselves for confirmation, which being stated,
I conceive that the truth I contend for will fol-
low necessarily, and appear as a thing obvious
to all. First, the blood is incessantly transmit-
ted by the action of the heart from the vena
cava to the arteries in such quantity that it can-
not be supplied from the ingesta, and in such
wise that the whole mass must very quickly
pass through the organ; second, the blood un-
der the influence of the arterial pulse enters
and is impelled in a continuous, equable, and
incessant stream through every part and mem-
ber of the body, in much larger quantity than
were sufficient for nutrition, or than the whole
mass of fluids could supply; third, the veins in
like manner return this blood incessantly to the
heart from all parts and members of the body.
These points proved, I conceive it will be mani-
fest that the blood circulates, revolves, pro-
pelled and then returning, from the heart to
the extremities, from the extremities to the
heart, and thus that it performs a kind of circu-
lar motion.
Let us assume, either arbitrarily or from ex-
periment, the quantity of blood which the left
ventricle of the heart will contain when dis-
tended to be, say two ounces, three ounces, one
ounce and a half— in the dead body I have
found it to hold upwards of two ounces. Let us
assume further, how much less the heart will
hold in the contracted than in the dilated state;
and how much blood it will project into the
aorta upon each contraction— and all the world
allows that with the systole something is al-
ways projected, a necessary consequence dem-
onstrated in the third chapter, and obvious
from the structure of the valves; and let us sup-
pose as approaching the truth that the fourth,
or fifth, or sixth, or even but the eighth part of
its charge is thrown into the artery at each con-
traction; this would give either half an ounce,
or three drachms, or one drachm of blood as
propelled by the heart at each pulse into the
aorta; which quantity, by reason of the valves
at the root of the vessel, can by no means return
into the ventricle. Now in the course of half an
hour, the heart will have made more than one
thousand beats, in some as many as two, three,
and even four thousand. Multiplying the num-
ber of drachms propelled by the number of
pulses, we shall have either one thousand half
ounces, or one thousand times three drachms,
or a like proportional quantity of blood, ac-
cording to the amount which we assume as pro-
pelled with each stroke of the heart, sent from
this organ into the artery; a larger quantity in
every case than is contained in the whole body !
MOTION OF THE HEART
287
In the same way, in the sheep or dog, say that
but a single scruple of blood passes with each
stroke of the heart, in one half hour we should
have one thousand scruples, or about three
pounds and a half of blood injected into the
aorta; but the body of neither animal contains
above four pounds of blood, a fact which I have
myself ascertained in the case of the sheep.
Upon this supposition, therefore, assumed
merely as a ground for reasoning, we see the
whole mass of blood passing through the heart,
from the veins to the arteries, and in like man-
ner through the lungs.
But let it be said that this does not take place
in half an hour, but in an hour, or even in a
day; any way it is still manifest that more blood
passes through the heart in consequence of its
action, than can either be supplied by the
whole of the ingesta, or than can be contained
in the veins at the same moment.
Nor can it be allowed that the heart in con-
tracting sometimes propels and sometimes does
not propel, or at most propels but very little, a
mere nothing, or an imaginary something: all
this, indeed, has already been refuted; and is,
besides, contrary both to sense and reason. For
if it be a necessary effect of the dilatation of the
heart that its ventricles become filled with
blood, it is equally so that, contracting, these
cavities should expel their contents; and this
not in any trifling measure, seeing that neither
are the conduits small, nor the contractions
few in number, but frequent, and always in
some certain proportion, whether it be a third
or a sixth, or an eighth, to the total capacity of
the ventricles, so that a like proportion of blood
must be expelled, and a like proportion re-
ceived with each stroke of the heart, the capa-
city of the ventricle contracted always bearing
a certain relation to the capacity of the ventri-
cle when dilated. And since in dilating, the
ventricles cannot be supposed to get filled with
nothing, or with an imaginary something; so in
contracting they never expel nothing or aught
imaginary, but always a certain something, viz.,
blood, in proportion to the amount of the con-
traction. Whence it is to be inferred, that if at
one stroke the heart in man, the ox or the sheep,
ejects but a single drachm of blood, and there
are one thousand strokes in half an hour, in this
interval there will have been ten pounds, five
ounces expelled: were there with each stroke
two drachms expelled, the quantity would of
course amount to twenty pounds and ten
ounces; were there half an ounce, the quantity
would come to forty-one pounds and eight
ounces; and were there one ounce it would be
as much as eighty- three pounds and four
ounces; the whole of which, in the course of one
half hour, would have been transfused from the
veins to the arteries. The actual quantity of
blood expelled at each stroke of the heart, and
the circumstances under which it is either
greater or less than ordinary, I leave for par-
ticular determination afterwards, from numer-
ous observations which I have made on the sub-
ject.
Meantime this much I know, and would here
proclaim to all that the blood is transfused at
one time in larger, at another in smaller quan-
tity; and that the circuit of the blood is ac-
complished now more rapidly, now more slow-
ly, according to the temperament, age, &c. of
the individual, to external and internal circum-
stances, to naturals and non-naturals—sleep,
rest, food, exercise, affections of the mind, and
the like. But indeed, supposing even the small-
est quantity of blood to be passed through the
heart and the lungs with each pulsation, a
vastly greater amount would still be thrown
into the arteries and whole body than could by
any possibility be supplied by the food con-
sumed; in short it could be furnished in no
other way than by making a circuit and re-
turning.
This truth, indeed, presents itself obviously
before us when we consider what happens in
the dissection of living animals; the great ar-
tery need not be divided, but a very small
branch only (as Galen even proves in regard to
man), to have the whole of the blood in the
body, as well that of the veins as of the arteries,
drained away in the course of no long time —
some half hour or less. Butchers are well aware
of the fact and can bear witness to it; for, cut-
ting the throat of an ox and so dividing the ves-
sels of the neck, in less than a quarter of an
hour they have all the vessels bloodless— the
whole mass of blood has escaped. The same
thing also occasionally occurs with great rapid-
ity in performing amputations and removing
turnours in the human subject.
Nor would this argument lose any of its
force, did anyone say that in killing animals in
the shambles, and performing amputations, the
blood escaped in equal, if not perchance in
larger quantity by the veins than by the ar-
teries. The contrary of this statement, indeed,
is certainly the truth; the veins, in fact, collap-
sing, and being without any propelling power,
and further, because of the impediment of the
valves, as I shall show immediately, pour out
288
WILLIAM HARVEY
but very little blood; whilst the arteries spout
it forth with force abundantly, impetuously,
and as if it were propelled by a syringe. And
then the experiment is easily tried of leaving
the vein untouched, and only dividing the ar-
tery in the neck of a sheep or dog, when it will
be seen with what force, in what abundance,
and how quickly, the whole blood in the body,
of the veins as well as of the arteries, is emptied.
But the arteries receive blood from the veins in
no other way than by transmission through the
heart, as we have already seen; so that if the
aorta be tied at the base of the heart, and the
carotid or any other artery be opened, no one
will now be surprised to find it empty, and the
veins only replete with blood.
And now the cause is manifest, wherefore in
our dissections we usually find so large a quan-
tity of blood in the veins, so little in the arter-
ies; wherefore there is much in the right ven-
tricle, little in the left; circumstances which
probably led the ancients to believe that the
arteries (as their name implies) contained noth-
ing but spirits during the life of an animal. The
true cause of the difference is this perhaps: that
as there is no passage to the arteries, save
through the lungs and heart, when an animal
has ceased to breathe and the lungs to move,
the blood in the pulmonary artery is prevented
from passing into the pulmonary veins, and
from thence into the left ventricle of the heart;
just as we have already seen the same transit
prevented in the embryo, by the want of move-
ment in the lungs and the alternate opening
and shutting of their minute orifices and invis-
ible pores. But the heart not ceasing to act at
the same precise moment as the lungs, but sur-
viving them and continuing to pulsate for a
time, the left ventricle and arteries go on dis-
tributing their blood to the body at large and
sending it into the veins; receiving none from
the lungs, however, they are soon exhausted,
and left, as it were, empty. But even this fact
confirms our views, in no trifling manner, see-
ing that it can be ascribed to no other than the
cause we have just assumed.
Moreover, it appears from this that the more
frequently or forcibly the arteries pulsate, the
more speedily will the body be exhausted in an
hemorrhagy. Hence, also, it happens, that in
fainting fits and in states of alarm, when the
heart beats more languidly and with less
force, hemorrhages are diminished or arrested.
Still further, it is from this that after death,
when the heart has ceased to beat, it is impos-
sible by dividing either the jugular or femoral
veins and arteries, by any effort to force out
more than one half of the whole mass of the
blood. Neither could the butcher, did he neg-
lect to cut the throat of the ox which he has
knocked on the head and stunned, until the
heart had ceased beating, ever bleed the car-
cass effectually.
Finally, we are now in a condition to suspect
wherefore it is that no one has yet said anything
to the purpose upon the anastomosis of the
veins and arteries, either as to where or how it
is effected, or for what purpose. I now enter
upon the investigation of the subject.
CHAPTER 10. The fast position: of the quantity of
blood passing from the veins to the arteries; and that
there is a circuit of the blood, freed from objections ',
and further confirmed by experiment
So far our first position is confirmed, whether
the thing be referred to calculation or to experi-
ment and dissection, viz., that the blood is in-
cessantly infused into the arteries in larger
quantities than it can be supplied by the food;
so that the whole passing over in a short space
of time, it is matter of necessity that the blood
perform a circuit, that it return to whence it
set out.
But if anyone shall here object that a large
quantity may pass through and yet no neces-
sity be found for a circulation, that all may
come from the meat and drink consumed, and
quote as an illustration the abundant supply of
milk in the mammae— for a cow will give three,
four, and even seven gallons and more in a day,
and a woman two or three pints whilst nursing
a child or twins, which must manifestly be de-
rived from the food consumed; it may be an-
swered, that the heart by computation does as
much and more in the course of an hour or two.
And if not yet convinced, he shall still insist,
that when an artery is divided a preternatural
route is, as it were, opened, and that so the
blood escapes in torrents, but that the same
thing does not happen in the healthy and unin-
jured body when no outlet is made; and that in
arteries filled, or in their natural state, so large
a quantity of blood cannot pass in so short a
space of time as to make any return necessary;
to all this it may be answered, that from the
calculation already made, and the reasons as-
signed, it appears that, by so much as the heart
in its dilated state contains in addition to its
contents in the state of constriction, so much in
a general way must it emit upon each pulsation,
and in such quantity must the blood pass, the
body being healthy and naturally constituted.
MOTION OF THE HEART
289
But in serpents, and several fishes, by tying
the veins some way below the heart, you will
perceive a space between the ligature and the
heart speedily to become empty; so that, un-
less you would deny the evidence of your
senses, you must needs admit the return of the
blood to the heart. The same thing will also
plainly appear when we come to discuss our
second position.
Let us here conclude with a single example,
confirming all that has been said, and from
which everyone may obtain conviction
through the testimony of his own eyes.
If a live snake be laid open, the heart will be
seen pulsating quietly, distinctly, for more
than an hour, moving like a worm, contracting
in its longitudinal dimensions (for it is of an
oblong shape), and propelling its contents; be-
coming of a paler colour in the systole, of a
deeper tint in the diastole ; and almost all things
else by which I have already said that the truth
I contend for is established, only that here
everything takes place more slowly, and is more
distinct. This point in particular may be ob-
served more clearly than the noonday sun: the
vena cava enters the heart at its lower part, the
artery quits it at the superior part; the vein be-
ing now seized either with forceps or between
the finger and thumb, and the course of the
blood for some space below the heart inter-
rupted, you will perceive the part that inter-
venes between the fingers and the heart almost
immediately to become empty, the blood being
exhausted by the action of the heart; at the
same time the heart will become of a much
paler colour, even in its state of dilatation, than
it was before; it is also smaller than at first, from
wanting blood; and then it begins to beat more
slowly, so that it seems at length as if it were
about to die. But the impediment to the flow
of blood being removed, instantly the colour
and the size of the heart are restored.
If, on the contrary, the artery instead of the
vein be compressed or tied, you will observe
the part between the obstacle and the heart,
and the heart itself, to become inordinately dis-
tended, to assume a deep purple or even livid
colour, and at length to be so much oppressed
with blood that you will believe it about to be
choked; but the obstacle removed, all things
immediately return to their pristine state —
the heart to its colour, size, stroke, &c.
Here then we have evidence of two kinds of
death: extinction from deficiency, and suffoca-
tion from excess. Examples of both have now
been set before you, and you have had oppor-
tunity of viewing the truth contended for with
your own eyes in the heart.
CHAPTER 11. The second position is demonstrated
THAT this may the more clearly appear to
everyone, I have here to cite certain experi-
ments, from which it seems obvious that the
blood enters a limb by the arteries, and returns
from it by the veins; that the arteries are the
vessels carrying the blood from the heart, and
the veins the returning channels of the blood
to the heart; that in the limbs and extreme
parts of the body the blood passes either im-
mediately by anastomosis from the arteries in-
to the veins, or mediately by the pores of the
flesh, or in both ways, as has already been said
in speaking of the passage of the blood through
the lungs; whence it appears manifest that in
the circuit the blood moves from thence hither,
and from hence thither; from the centre to the
extremities, to wit; and from the extreme parts
back again to the centre. Finally, upon grounds
of calculation, with the same elements as be-
fore, it will be obvious that the quantity can
neither be accounted for by the ingesta, nor
yet be held necessary to nutrition.
The same thing will also appear in regard to
ligatures, and wherefore they are said to draw;
though this is neither from the heat, nor the
pain, nor the vacuum they occasion, nor indeed
from any other cause yet thought of; it will also
explain the uses and advantages to be derived
from ligatures in medicine, the principle upon
which they either suppress or occasion hemor-
rhage; how they induce sloughing and more ex-
tensive mortification in extremities; and how
they act in the castration of animals and the
removal of warts and fleshy tumours. But it has
come to pass, from no one having duly weighed
and understood the causes and rationale of
these various effects, that though almost all,
upon the faith of the old writers, recommend
ligatures in the treatment of disease, yet very
few comprehend their proper employment, or
derive any real assistance from them in effect-
ing cures.
Ligatures are either very tight or of middling
tightness. A ligature I designate as tight or per-
fect when it is drawn so close about an extrem-
ity that no vessel can be felt pulsating beyond
it. Such a ligature we use in amputations to
control the flow of blood; and such also are em-
ployed in the castration of animals and the re-
moval of tumours. In the latter instances, all
afHux of nutriment and heat being prevented
by the ligature, we see the testes and large
apo
WILLIAM HARVEY
fleshy tumours dwindle, and die, and finally
fall off.
Ligatures of middling tightness I regard as
those which compress a limb firmly all around,
but short of pain, and in such a way as still suf-
fers a certain degree of pulsation to be felt in
the artery beyond them. Such a ligature is in
use in bloodletting, an operation in which the
fillet applied above the elbow is not drawn so
tight but that the arteries at the wrist may still
be felt beating under the finger.
Now let any one make an experiment upon
the arm of a man, either using such a fillet as is
employed in bloodletting, or grasping the limb
lightly with his hand, the best subject for it
being one who is lean, and who has large veins,
and the best time after exercise, when the body
is warm, the pulse is full, and the blood carried
in larger quantity to the extremities, for all
then is more conspicuous; under such circum-
stances let a ligature be thrown about the ex-
tremity, and drawn as tightly as can be borne,
it will first be perceived that beyond the liga-
ture, neither in the wrist nor anywhere else, do
the arteries pulsate, at the same time that im-
mediately above the ligature the artery begins
to rise higher at each diastole, to throb more
violently, and to swell in its vicinity with a
kind of tide, as if it strove to break through
and overcome the obstacle to its current; the
artery here, in short, appears as if it were pre-
ternaturally full. The hand under such circum-
stances retains its natural colour and appear-
ance; in the course of time it begins to fall some-
what in temperature, indeed, but nothing is
drawn into it.
After the bandage has been kept on for some
short time in this way, let it be slackened a
little, brought to that state or term of middling
tightness which is used in bleeding, and it will
be seen that the whole hand and arm will in-
stantly become deeply suffused and distended,
and the veins show themselves tumid and knot-
ted; after ten or fifteen pulses of the artery, the
hand will be perceived excessively distended,
injected, gorged with blood, drawn, as it is said,
by this middling ligature, without pain, or
heat, or any horror of a vacuum, or any other
cause yet indicated.
If the finger be applied over the artery as it is
pulsating by the edge of the fillet, at the mo-
ment of slackening it, the blood will be felt to
glide through, as it were, underneath the fin-
ger; and he, too, upon whose arm the experi-
ment is made, when the ligature is slackened, is
distinctly conscious of a sensation of warmth,
and of something, viz., a stream of blood sud-
denly making its way along the course of the
vessels and diffusing itself through the hand,
which at the same time begins to feel hot, and
becomes distended.
As we had noted, in connexion with the tight
ligature, that the artery above the bandage was
distended and pulsated, not below it, so, in the
case of the moderately tight bandage, on the
contrary, do we find that the veins below, never
above, the fillet, swell, and become dilated,
whilst the arteries shrink; and such is the degree
of distention of the veins here that it is only
very strong pressure that will force the blood
beyond the fillet, and cause any of the veins in
the upper part of the arm to rise.
From these facts it is easy for every careful
observer to learn that the blood enters an ex-
tremity by the arteries; for when they are effec-
tually compressed nothing is drawn to the mem-
ber; the hand preserves its colour; nothing flows
into it, neither is it distended; but when the
pressure is diminished, as it is with the bleeding
fillet, it is manifest that the blood is instantly
thrown in with force, for then the hand begins
to swell; which is as much as to say that when
the arteries pulsate the blood is flowing through
them, as it is when the moderately tight liga-
ture is applied; but where they do not pulsate,
as, when a tight ligature is used, they cease from
transmitting any thing; they are only distended
above the part where the ligature is applied.
The veins again being compressed, nothing can
flow through them; the certain indication of
which is that below the ligature they are much
more tumid than above it and than they usu-
ally appear when there is no bandage upon the
arm.
It therefore plainly appears that the ligature
prevents the return of the blood through the
veins to the parts above it, and maintains those
beneath it in a state of permanent distention.
But the arteries, in spite of its pressure, and
under the force and impulse of the heart, send
on the blood from the internal parts of the body
to the parts beyond the bandage. And herein
consists the difference between the tight and
the medium bandage, that the former not only
prevents the passage of the blood in the veins,
but in the arteries also; the latter, however,
whilst it does not prevent the pulsific force
from extending beyond it, and so propelling
the blood to the extremities of the body, com-
presses the veins, and greatly or altogether im-
pedes the return of the blood through them.
Seeing, therefore that the moderately tight
MOTION OF THE HEART
291
ligature renders the veins turgid, and the whole
hand full of blood, I ask, whence is this? Does
the blood accumulate below the ligature com-
ing through the veins, or through the arteries,
or passing by certain secret pores ? Through the
veins it cannot come; still less can it come by
any system of invisible pores; it must needs
arrive by the arteries, then, in conformity with
all that has been already said. That it cannot
flow in by the veins appears plainly enough
from the fact that the blood cannot be forced
towards the heart unless the ligature be re-
moved; when on a sudden all the veins collapse,
and disgorge themselves of their contents into
the superior parts, the hand at the same time
resuming its natural pale colour, the tumefac-
tion and the stagnating blood have disappeared.
Moreover, he whose arm or wrist has thus
been bound for some little time with the me-
dium bandage, so that it has not only got swol-
len and livid but cold, when the fillet is undone
is aware of something cold making its way up-
wards along with the returning blood, and
reaching the elbow or the axilla. And I have
myself been inclined to think that this cold
blood rising upwards to the heart was the cause
of the fainting that often occurs after bloodlet-
ting: fainting frequently supervenes even in
robust subjects, and mostly at the moment of
undoing the fillet, as the vulgar say, from the
turning of the blood.
Further, when we see the veins below the lig-
ature instantly swell up and become gorged,
when from extreme tightness it is somewhat
relaxed, the arteries meantime continuing un-
affected, this is an obvious indication that the
blood passes from the arteries into the veins,
and not from the veins into the arteries, and
that there is either an anastomosis of the two
orders of vessels, or pores in the flesh and solid
parts generally that are permeable to the blood.
It is further an indication that the veins have
frequent communications with one another,
because they all become turgid together, whilst
under the medium ligature applied above the
elbow; and if any single small vein be pricked
with a lancet, they all speedily shrink, and dis-
burthening themselves into this they subside
almost simultaneously.
These considerations will enable anyone to
understand the nature of the attraction that is
exerted by ligatures, and perchance of fluxes
generally; how, for example, the veins when
compressed by a bandage of medium tightness
applied above the elbow, the blood cannot es-
cape, whilst it still continues to be driven in, to
wit, by the forcing power of the heart, by which
the parts are of necessity filled, gorged with
blood. And how should it be otherwise? Heat
and pain and the vis vacui draw, indeed; but in
such wise only that parts are filled, not preter-
naturally distended or gorged, not so suddenly
and violently overwhelmed with the charge of
blood forced in upon them, that the flesh is
lacerated and the vessels ruptured. Nothing of
the kind as an effect of heat, or pain, or the vacu-
um force, is either credible or demonstrable.
Besides, the ligature is competent to occasion
the afflux in question without either pain, or
heat, or vis vacui. Were pain in any way the
cause, how should it happen that, with the arm
bound above the elbow, the hand and fingers
should swell below the bandage, and their veins
become distended ? The pressure of the bandage
certainly prevents the blood from getting there
by the veins. And then, wherefore is there nei-
ther swelling nor repletion of the veins, nor any
sign or symptom of attraction or afflux, above
the ligature? But this is the obvious cause of
the preternatural attraction and swelling below
the bandage, and in the hand and fingers, that
the blood is entering abundantly, and with force,
but cannot pass out again.
Now is not this the cause of all tumefaction,
as indeed Avicenna has it, and of all oppressive
redundancy in parts, that the access to them is
open, but the egress from them is closed?
Whence it comes that they are gorged and tume-
fied. And may not the same thing happen in
local inflammations, where, so long as the swell-
ing is on the increase, and has not reached its ex-
treme term, a full pulse is felt in the part, es-
pecially when the disease is of the more acute
kind, and the swelling usually takes place most
rapidly. But these are matters for after dis-
cussion. Or does this, which occurred in my
own case, happen from the same cause ? Thrown
from a carriage upon one occasion, I struck my
forehead a blow upon the place where a twig of
the artery advances from the temple, and im-
mediately, within the time in which twenty
beats could have been made, I felt a tumour the
size of an egg developed, without either heat or
any great pain: the near vicinity of the artery
had caused the blood to be effused into the
bruised part with unusual force and quickness.
And now, too, we understand wherefore in
phlebotomy we apply our fillet above the part
that is punctured, not below it; did the flow
come from above, not from below, the bandage
in this case would not only be of no service, but
would prove a positive hinderance; it would
292
WILLIAM HARVEY
have to be applied below the orifice, in order to
have the flow more free, did the blood descend
by the veins from superior to inferior parts; but
as it is elsewhere forced through the extreme
arteries into the extreme veins, and the return
in these last is opposed by the ligature, so do
they fill and swell, and being thus filled and dis-
tended, they are made capable of projecting
their charge with force, and to a distance, when
any one of them is suddenly punctured; but the
fillet being slackened, and the returning chan-
nels thus left open, the blood forthwith no long-
er escapes, save by drops; and, as all the world
knows, if in performing phlebotomy the band-
age be either slackened too much or the limb be
bound too tightly, the blood escapes without
force, because in the one case the returning
channels are not adequately obstructed; in the
other the channels of influx, the arteries, are
impeded.
CHAPTER 12. That there is a circulation of the
blood is shown from the second position demon-
strated
IF these things be so, another point which I
have already referred to, viz., the continual pas-
sage of the blood through the heart will also be
confirmed. We have seen that the blood passes
from the arteries into the veins, not from the
veins into the arteries; we have seen, further,
that almost the whole of the blood may be with-
drawn from a puncture made in one of the cu-
taneous veins of the arm if a bandage properly
applied be used; we have seen, still further, that
the blood flows so freely and rapidly that not
only is the whole quantity which was contained
in the arm beyond the ligature, and before the
puncture was made, discharged, but the whole
which is contained in the body, both that of
the arteries and that of the veins.
Whence we must admit, first, that the blood
is sent along with an impulse, and that is urged
with force below the fillet; for it escapes with
force, which force it receives from the pulse and
power of the heart; for the force and motion of
the blood are derived from the heart alone.
Second, that the afflux proceeds from the heart,
and through the heart by a course from the
great veins; for it gets into the parts below the
ligature through the arteries, not through the
veins; and the arteries nowhere receive blood
from the veins, nowhere receive blood save and
except from the left ventricle of the heart. Nor
could so large a quantity of blood be drawn from
one vein (a ligature having been duly applied),
nor with such impetuosity, such readiness, such
celerity, unless through the medium of the im-
pelling power of the heart.
But if all things be as they are now repre-
sented, we shall feeel ourselves at liberty to cal-
culate the quantity of the blood, and to reason
on its circular motion. Should anyone, for in-
stance, in performing phlebotomy, suffer the
blood to flow in the manner it usually does, with
force and freely, for some half hour or so, no
question but that the greatest part of the blood
being abstracted, faintings and syncopes would
ensue, and that not only would the arteries but
the great veins also be nearly emptied of their
contents. It is only consonant with reason to
conclude that in the course of the half hour
hinted at, so much as has escaped has also passed
from the great veins through the heart into the
aorta. And further, if we calculate how many
ounces flow through one arm, or how many pass
in twenty or thirty pulsations under the medi-
um ligature, we shall have some grounds for esti-
mating how much passes through the other arm
in the same space of time, how much through
both lower extremities, how much through the
neck on either side, and through all the other
arteries and veins of the body, all of which have
been supplied with fresh blood; and as this blood
must have passed through the lungs and ventri-
cles of the heart, and must have come from the
great veins, we shall perceive that a circulation
is absolutely necessary, seeing that the quanti-
ties hinted at cannot be supplied immediately
from the ingesta, and are vastly more than can
be requisite for the mere nutrition of the parts.
It is still further to be observed that the truths
contended for are sometimes confirmed in an-
other way; for having tied up the arm properly,
and made the puncture duly, still, if from alarm
or any other causes, a state of faintness super-
venes, in which the heart always pulsates more
languidly, the blood does not flow freely, but
distils by drops only. The reason is that with
the somewhat greater than usual resistance of-
fered to the transit of the blood by the bandage,
coupled with the weaker action of the heart,
and its diminished impelling power, the stream
cannot make its way under the fillet; and fur-
ther, owing to the weak and languishing state
of the heart, the blood is not transferred in such
quantity as wont from the veins to the arteries
through the sinuses of that organ. So also, and
for the same reasons, are the menstrual fluxes of
women, and indeed hemorrhages of every kind,
controlled. And now, a contrary state of things
occurring, the patient getting rid of his fear and
recovering his courage, the pulsific power is in-
MOTION OF THE HEART
293
creased, the arteries begin again to beat with
greater force, and to drive the blood even into
the part that is bound; so that the blood now
springs from the puncture in the vein, and flows
in a continuous stream.
CHAPTER 13. The third position is confirmed; and
the circulation of the blood is demonstrated from it
THUS far have we spoken of the quantity of
blood passing through the heart and the lungs
in the centre of the body, and in like manner
from the arteries into the veins in the peri-
pheral parts and the body at large. We have
yet to explain, however, in what manner the
blood finds its way back to the heart from the ex-
tremities by the veins, and how and in what way
these are the only vessels that convey the blood
from the external to the central parts; which
done, I conceive that the three fundamental
propositions laid down for the circulation of the
blood will be so plain, so well established, so ob-
viously true, that they may claim general cre-
dence. Now the remaining position will be made
sufficiently clear from the valves which are
found in the cavities of the veins themselves,
from the uses of these, and from experiments
cognizable by the senses.
The celebrated Hieronymus Fabricius of
Aquapendente, a most skilful anatomist, and
venerable old man, or, as the learned Riolan will
have it, Jacobus Silvius, first gave representa-
tions of the valves in the veins, which consist of
raised or loose portions of the inner membranes
of these vessels, of extreme delicacy, and a sig-
moid or semilunar shape. They are situated at
different distances from one another, and di-
versely in different individuals; they are connate
at the sides of the veins; they are directed up-
wards or towards the trunks of the veins; the
two— for there are for the most part two togeth-
er— regard each other, mutually touch, and are
so ready to come into contact by their edges,
that if any thing attempt to pass from the trunks
into the branches of the veins, or from the great-
er vessels into the less, they completely prevent
it; they are further so arranged that the horns
of those that succeed are opposite the middle of
the convexity of those that precede, and so on
alternately.
The discoverer of these valves did not rightly
understand their use, nor have succeeding anat-
omists added anything to our knowledge: for
their office is by no means explained when we
are told that it is to hinder the blood, by its
weight, from all flowing into inferior parts; for
the edges of the valves in the jugular veins hang
downwards, and are so contrived that they pre-
vent the blood from rising upwards; the valves,
in a word, do not invariably look upwards, but
always towards the trunks of the veins, invari-
ably towards the seat of the heart. I, and indeed
others, have sometimes found valves in the
emulgent veins, and in those of the mesentery,
the edges of which were directed towards the
vena cava and vena portae. Let it be added that
there are no valves in the arteries, and that dogs,
oxen, &c., have in variably valves at the divisions
of their crural veins, in the veins that meet
towards the top of the os sacrum, and in those
branches which come from the haunches, in
which no such effect of gravity from the erect
positon was to be apprehended. Neither are
there valves in the jugular veins for the purpose
of guarding against apoplexy, as some have said;
because in sleep the head is more apt to be in*-
fluenced by the contents of the carotid arteries.
Neither are the valves present, in order that the
blood may be retained in the divarications or
smaller trunks and minuter branches, and not be
suffered to flow entirely into the more open and
capacious channels; for they occur where there
are no divarications; although it must be owned
that they are most frequent at the points where
branches join. Neither do they exist for the pur-
pose of rendering the current of blood more slow
from the centre of the body; for it seems likely
that the blood would be disposed to flow with
sufficient slowness of its own accord, as it would
have to pass from larger into continually smaller
vessels, being separated from the mass and foun-
tain head, and attaining from warmer into cold-
er places.
But the valves are solely made and instituted
lest the blood should pass from the greater into
the lesser veins, and either rupture them or
cause them to become varicose; lest, instead of
advancing from the extreme to the central parts
of the body, the blood should rather proceed
along the veins from the centre to the extremi-
ties; but the delicate valves, while they readily
open in the right direction, entirely prevent all
such contrary motion, being so situated and ar-
ranged, that if anything escapes, or is less per-
fectly obstructed by the cornua of the one above,
the fluid passing, as it were, by the chinks be-
tween the cornua, it is immediately received on
the convexity of the one beneath, which is
placed transversely with reference to the for-
mer, and so is effectually hindered from getting
any farther.
And this I have frequently experienced in my
dissections of the veins: if I attempted to pass
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WILLIAM HARVEY
a probe from the trunk of the veins into one of
the smaller branches, whatever care I took I
found it impossible to introduce it far any way,
by reason of the valves; whilst, on the contrary,
it was most easy to push it along in the opposite
direction, from without inwards, or from the
branches towards the trunks and roots. In many
places two valves are so placed and fitted that
when raised they come exactly together in the
middle of the vein, and are there united by the
contact of their margins; and so accurate is the
adaptation, that neither by the eye nor by any
other means of examination can the slightest
chink along the line of contact be perceived. But
if the probe be now introduced from the ex-
treme towards the more central parts, the valves,
like the floodgates of a river, give way, and are
most readily pushed aside. The effect of this ar-
rangement plainly is to prevent all motion of
the blood from the heart and vena cava, wheth-
er it be upwards towards the head, or downwards
towards the feet, or to either side towards the
arms, not a drop can pass; all motion of the
blood, beginning in the larger and tending
towards the smaller veins, is opposed and re-
sisted by them; whilst the motion that proceeds
from the lesser to end in the larger branches is
favoured, or, at all events, a free and open pas-
sage is left for it.
But that this truth may be made the more
apparent, let an arm be tied up above the elbow
as if for phlebotomy (AA,fig. i). At intervals
in the course of the veins, especially in labouring
people and those whose veins are large, certain
knots or elevations (B, C, D, E, F) will be per-
ceived, and this not only at the places where a
branch is received (E, F), but also where none
enters (C, D): these knots or risings are all
formed by valves, which thus show themselves
externally. And now if you press the blood from
the space above one of the valves, from H to
0, (fig. 2), and keep the point of a finger upon
the vein inferiorly, you will see no influx of
blood from above; the portion of the vein be-
tween the point of the finger and the valve O
will be obliterated; yet will the vessel continue
sufficiently distended above that valve (O, G).
The blood being thus pressed out, and the vein
emptied, if you now apply a finger of the other
hand upon the distended part of the vein above
the valve O, (fig. 3), and press downwards, you
will find that you cannot force the blood through
or beyond the valve; but the greater effort you
use, you will only see the portion of vein that is
between thefinger and the valve become more dis-
tended, that portion of the vein which is below
the valve remaining all the while empty (//,
0,fig. 3)-
It would therefore appear that the function
of the valves in the veins is the same as that of
the three sigmoid valves which we find at the
commencement of the aorta and pulmonary ar-
tery, viz., to prevent all reflux of the blood that
is passing over them.
Further, the arm being bound as before, and
the veins looking full and distended, if you press
at one part in the course of a vein with the point
of a finger (L, fig. 4), and then with another
finger streak the blood upwards beyond the next
valve (AQ, you will perceive that this portion of
the vein continues empty (L, AQ, and that the
blood cannot retrograde, precisely as we have
already seen the case to be in fig. 2; but the fin-
ger first applied (H,fig. 2, L,fig. 4), being re-
moved, immediately the vein is filled from be-
low, and the arm becomes as it appears at D C,
fig. i. That the blood in the veins therefore pro-
ceeds from inferior or more remote to superior
parts, and towards the heart, moving in these
vessels in this and not in the contrary direction,
appears most obviously. And although in some
places the valves, by not acting with such per-
fect accuracy, or where there is but a single
valve, do not seem totally to prevent the pas-
sage of the blood from the centre, still the
greater number of them plainly do so; and then,
where things appear contrived more negligently,
this is compensated either by the more frequent
occurrence or more perfect action of the suc-
ceeding valves or in some other way: the veins,
in short, as they are the free and open conduits
of the blood returning to the heart, so are they
effectually prevented from serving as its chan-
nels of distribution from the heart.
But this other circumstance has to be noted:
the arm being bound, and the veins made tur-
gid, and the valves prominent, as before, apply
the thumb or finger over a vein in the situation
of one of the valves in such a way as to compress
it, and prevent any blood from passing upwards
from the hand; then, with a finger of the other
hand, streak the blood in the vein upwards till
it has passed the next valve above (N,fig. 4), the
vessel now remains empty ; but the finger at L be-
ing removed for an instant, the vein is immedi-
ately filled from below; apply the finger again,
and having in the same manner streaked the
blood upwards, again remove the finger below,
and again the vessel becomes distended as before ;
and this repeat, say a thousand times, in a short
space of time. And now compute the quantity
of blood which you have thus pressed up beyond
MOTION OF THE HEART
295
Fig. 2
Fig. 3
Fig. 4
the valve, and then multiplying the assumed
quantity by one thousand, you will find that so
much blood has passed through a certain portion
of the vessel; and I do now believe that you will
find yourself convinced of the circulation of the
blood, and of its rapid motion. But if in this ex-
periment you say that a violence is done to
nature, I do not doubt but that, if you proceed
in the same way, only taking as great a length
of vein as possible, and merely remark with what
rapidity the blood flows upwards, and fills the
vessel from below, you will come to the same
conclusion.
CHAPTER 14. Conclusion of the demonstration of
the circulation
AND now I may be allowed to give in brief my
view of the circulation of the blood, and to pro-
pose it for general adoption.
Since all things, both argument and ocular
demonstration, show that the blood passes
through the lungs and heart by the action of
296
WILLIAM HARVEY
the auricles and ventricles, and is sent for distri-
bution to all parts of the body, where it makes
its way into the veins and pores of the flesh,
and then flows by the veins from the circum-
ference on every side to the centre, from the
lesser to the greater veins, and is by them fi-
nally discharged into the vena cava and right
auricle of the heart, and this in such a quantity
or in such a flux and reflux thither by the ar-
teries, hither by the veins, as cannot possibly
be supplied by the ingesta, and is much greater
than can be required for mere purposes of nu-
trition; it is absolutely necessary to conclude
that the blood in the animal body is impelled
in a circle, and is in a state of ceaseless motion;
that this is the act or function which the heart
performs by means of its pulse; and that it is
the sole and only end of the motion and con-
traction of the heart.
CHAPTER 15. The circulation of the blood is
further confirmed by probable reasons
IT will not be foreign to the subject if I here
show further, from certain familiar reasonings,
that the circulation is matter both of conven-
ience and necessity. In the first place, since
death is a corruption which takes place through
deficiency of heat,1 and since all living things
are warm, all dying things cold, there must be
a particular seat and fountain, a kind of home
and hearth, where the cherisher of nature, the
original of the native fire, is stored and pre-
served; whence heat and life are dispensed to
all parts as from a fountain head; whence sus-
tenance may be derived; and upon which con-
coction and nutrition, and all vegetative energy
may depend. Now, that the heart is this place,
that the heart is the principle of life, and that
all passes in the manner just mentioned, I trust
no one will deny.
The blood, therefore, required to have mo-
tion, and indeed such a motion that it should
return again to the heart; for sent to the exter-
nal parts of the body far from its fountain, as
Aristotle says, and without motion, it would
become congealed. For we see motion generat-
ing and keeping up heat and spirits under all
circumstances, and rest allowing them to es-
cape and be dissipated. The blood, therefore,
become thick or congealed by the cold of the
extreme and outward parts, and robbed of its
spirits, just as it is in the dead, it was impera-
tive that from its fount and origin, it should
again receive heat and spirits, and all else req-
1 Aristotle, On Youth, Life, and Breathing, 23, 24;
On the Parts of Animals, II, 7.
uisite to its preservation— that, by returning,
it should be renovated and restored.
We frequently see how the extremities are
chilled by the external cold, how the nose and
cheeks and hands look blue, and how the blood,
stagnating in them as in the pendent or lower
parts of a corpse, becomes of a dusky hue; the
limbs at the same time getting torpid, so that
they can scarcely be moved, and seem almost
to have lost their vitality. Now they can by
no means be so effectually, and especially so
speedily restored to heat and colour and life, as
by a new afflux and appulsion of heat from its
source. But how can parts attract in which the
heat and life are almost extinct ? Or how should
they whose passages are filled with condensed
and frigid blood, admit fresh aliment — reno-
vated blood — unless they had first got rid of
their old contents ? Unless the heart were truly
that fountain where life and heat are restored
to the refrigerated fluid, and whence new
blood, warm, imbued with spirits, being sent
out by the arteries, that which has become
cooled and effete is forced on, and all the par-
ticles recover their heat which was failing, and
their vital stimulus well-nigh exhausted.
Hence it is that if the heart be unaffected,
life and health may be restored to almost all the
other parts of the body; but the heart being
chilled, or smitten with any serious disease, it
seems matter of necessity that the whole ani-
mal fabric should suffer and fall into decay.
When the source is corrupted, there is nothing,
as Aristotle says,2 which can be of service either
to it or aught that depends on it. And hence, by
the way, it may perchance be wherefore grief,
and love, and envy, and anxiety, and all affec-
tions of the mind of a similar kind are accom-
panied with emaciation and decay, or with
cacochemy and crudity, which engender all
manner of diseases and consume the body of
man. For every affection of the mind that is
attended with either pain or pleasure, hope or
fear, is the cause of an agitation whose influence
extends to the heart, and there induces change
from the natural constitution, in the tempera-
ture, the pulse and the rest, which impairing all
nutrition in its source and abating the powers
at large, it is no wonder that various forms of
incurable disease in the extremities and in the
trunk are the consequence, inasmuch as in such
circumstances the whole body labours under
the effects of vitiated nutrition and a want ol
native heat.
Moreover, when we see that all animals live
2 On the Parts of Animals, in.
MOTION OF THE HEART
297
through food concocted in their interior, it is
imperative that the digestion and distribution
be perfect; and, as a consequence, that there be
a place and receptacle where the aliment is per-
fected and whence it is distributed to the sev-
eral members. Now this place is the heart, for it
is the only organ in the body which contains
blood for the general use; all the others receive
it merely for their peculiar or private advan-
tage, just as the heart also has a supply for its
own especial behoof in its coronary veins and
arteries; but it is of the store which the heart
contains in its auricles and ventricles that I here
speak; and then the heart is the only organ
which is so situated and constituted that it can
distribute the blood in due proportion to the
several parts of the body, the quantity sent to
each being according to the dimensions of the
artery which supplies it, the heart serving as a
magazine or fountain ready to meet its de-
mands.
Further, a certain impulse or force, as well as
an impeller or forcer, such as the heart, was re-
quired to effect this distribution and motion of
the blood; both because the blood is disposed
from slight causes, such as cold, alarm, horror,
and the like, to collect in its source, to concen-
trate like parts to a whole, or the drops of water
spilt upon a table to the mass of liquid; and
then because it is forced from the capillary
veins into the smaller ramifications, and from
these into the larger trunks by the motion of
the extremities and the compression of the
muscles generally. The blood is thus more dis-
posed to move from the circumference to the
centre than in the opposite direction, were
there even no valves to oppose its motion;
whence that it may leave its source and enter
more confined and colder channels, and flow
against the direction to which it spontaneously
inclines, the blood requires both force and an
impelling power. Now such is the heart and the
heart alone, and that in the way and manner
already explained.
CHAPTER 16. The circulation of the blood is
further proved from certain consequences
THERE are still certain phenomena, which, tak-
en as consequences of this truth assumed as
proven, are not without their use in exciting
belief, as it were, a posteriori; and which, al-
though they may seem to be involved in much
doubt and obscurity, nevertheless readily ad-
mit of having reasons and causes assigned for
them. The phenomena alluded to are those that
present themselves in connexion with contag-
ions, poisoned wounds, the bites of serpents
and rabid animals, lues venerea and the like.
We sometimes see the whole system contami-
nated, though the part first infected remains
sound; the lues venerea has occasionally made
its attack with pains in the shoulders and head,
and other symptoms, the genital organs being
all the while unaffected; and then we know
that the wound made by a rabid dog having
healed, fever and a train of disastrous symptoms
nevertheless supervene. Whence it appears
that the contagion impressed upon or deposited
in a particular part, is by and by carried by the
returning current of blood to the heart, and by
that organ is sent to contaminate the whole
body.
In tertian fever, the morbific cause seeking
the heart in the first instance, and hanging
about the heart and lungs, renders the patient
short-winded, disposed to sighing, indisposed
to exertion; because the vital principle is op-
pressed and the blood forced into the lungs and
rendered thick, does not pass through their sub-
stance (as I have myself seen in opening the
bodies of those who had died in the beginning
of the attack) when the pulse is always fre-
quent, small, and occasionally irregular; but the
heat increasing, the matter becoming attenu-
ated, the passages forced, and the transit made,
the whole body begins to rise in temperature,
and the pulse becomes fuller, stronger — the
febrile paroxysm is fully formed, whilst the pre-
ternatural heat kindled in the heart is thence
diffused by the arteries through the whole body
along with the morbific matter, which is in this
way overcome and dissolved by nature.
When we perceive, further, that medicines
applied externally exert their influence on the
body just as if they had been taken internally,
the truth we are contending for is confirmed.
Colocynth and aloes move the belly, canthar-
ides excite the urine, garlic applied to the soles of
the feet assists expectoration, cordials strength-
en, and an infinite number of examples of the
same kind might be cited. It will not, therefore,
be found unreasonable perchance, if we say that
the veins, by means of their orifices, absorb
some of the things that are applied externally
and carry this inwards with the blood, not
otherwise, it may be, than those of the mesen-
tery imbibe the chyle from the intestines and
carry it mixed with the blood to the liver. For
the blood entering the mesentery by the coeliac
artery, and the superior and inferior mesen-
teries, proceeds to the intestines, from which,
along with the chyle that has been attracted
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WILLIAM HARVEY
into the veins, it returns by their numerous
ramifications into the vena portae of the liver,
and from this into the vena cava, and this in
such wise that the blood in these veins has the
same colour and consistency as in other veins,
in opposition to what many believe to be the
fact. Nor indeed can we imagine two contrary
motions in any capillary system— the chyle up-
wards, the blood downwards. This could scarcely
take place, and must be held as altogether im-
probable. But is not the thing rather arranged
as it is by the consummate providence of na-
ture? For were the chyle mingled with the
blood, the crude with the concoted, in equal
proportions, the result would not be concoc-
tion, transmutation, and sanguification, but
rather, and because they are severally active
and passive, a mixture or combination, or me-
dium compound of the two, precisely as happens
when wine is mixed with water and syrup.
But when a very minute quantity of chyle is
mingled with a very large quantity of circulat-
ing blood, a quantity of chyle that bears no
kind of proportion to the mass of blood, the
effect is the same, as Aristotle says, as when a
drop of water is added to a cask of wine, or the
contrary; the mass does not then present itself
as a mixture, but is still sensibly either wine or
water. So in the mesenteric veins of an animal
we do not find either chyme or chyle and blood,
blended together or distinct, but only blood,
the same in colour, consistency, and other sen-
sible properties, as it appears in the veins gen-
erally. Still as there is a certain though small
and inappreciable proportion of chyle or un-
concocted matter mingled with this blood, na-
ture has interposed the liver, in whose mean-
dering channels it suffers delay and undergoes
additional change, lest arriving prematurely and
crude at the heart, it should oppress the vital
principle. Hence in the embryo, there is almost
no use for the liver, but the umbilical vein
passes directly through, a foramen or anastom-
osis existing from the vena portae, so that the
blood returns from the intestines of the foetus,
not through the liver, but into the umbilical
vein mentioned, and flows at once into the heart,
mingled with the natural blood which is return-
ing from the placenta; whence also it is that in
the development of the foetus the liver is one
of the organs that is last formed; I have ob-
served all the members perfectly marked out in
the human foetus, even the genital organs,
whilst there was yet scarcely any trace of the
liver. And indeed at the period when all the
parts, like the heart itself in the beginning, are
still white, and save in the veins there is no ap-
pearance of redness, you shall see nothing in the
seat of the liver but a shapeless collection, as it
were, of extravasated blood, which you might
take for the effects of a contusion or ruptured
vein.
But in the incubated egg there are, as it were,
two umbilical vessels, one from the albumen
passing entire through the liver, and going
straight to the heart; another from the yelk,
ending in the vena portae; for it appears that
the chick, in the first instance, is entirely formed
and nourished by the white; but by the yelk
after it has come to perfection and is excluded
from the shell; for this part may still be found
in the abdomen of the chick many days after
its exclusion, and is a substitute for the milk
to other animals.
But these matters will be better spoken of in
my observations on the formation of the foetus,
where many propositions, the following among
the number, will be discussed : wherefore is this
part formed or perfected first, that last? — and
of the several members: what part is the cause
of another? And many points having special
reference to the heart, such as: wherefore does
it first acquire consistency, and appear to pos-
sess life, motion, sense, before any other part of
the body is perfected, as Aristotle says in On
the Parts of Animals, m ? And so also of the
blood: wherefore does it precede all the rest?
And in what way does it possess the vital and
animal principle ? And show a tendency to mo-
tion, and to be impelled hither and thither, the
end for which the heart appears to be made ? In
the same way, in considering the pulse: where-
fore one kind of pulse should indicate death,
another recovery ? And so of all the other kinds
of pulse, what may be the cause and indication
of each. So also in the consideration of crises
and natural critical discharges; of nutrition, and
especially the distribution of the nutriment;
and of defluxions of every description. Finally,
reflecting on every part of medicine, physiol-
ogy, pathology, semeiotics, therapeutics, when
I see how many questions can be answered, how
many doubts resolved, how much obscurity il-
lustrated, by the truth we have declared, the
light we have made to shine, I see a field of such
vast extent in which I might proceed so far,
and expatiate so widely, that this my tractate
would not only swell out into a volume, which
was beyond my purpose, but my whole life,
perchance, would not suffice for its completion.
In this place, therefore, and that indeed in a
single chapter, I ^hall only endeavour to refer
MOTION OF THE HEART
299
the various particulars that present themselves
in the dissection of the heart and arteries to
their several uses and causes; for so I shall meet
with many things which receive light from the
truth I have been contending for, and which, in
their turn, render it more obvious. And indeed
I would have it confirmed and illustrated by
anatomical arguments above all others.
There is but a single point which indeed
would be more correctly placed among our ob-
servations on the use of the spleen, but which it
will not be altogether impertinent to notice in
this place incidentally. From the splenic branch
which passes into the pancreas, and from the
upper part, arise the posterior coronary, gas-
tric, and gastroepiploic veins, all of which are
distributed upon the stomach in numerous
branches and twigs, just as the mesenteric ves-
sels are upon the intestines; in like manner,
from the inferior part of the same splenic branch,
and along the back of the colon and rectum
proceed the hemorrhoidal veins. The blood re-
turning by these veins, and bringing the cruder
juices along with it, on the one hand from the
stomach, where they are thin, watery, and not
yet perfectly chylified; on the other thick and
more earthy, as derived from the faeces, but all
poured into this splenic branch, are duly tem-
pered by the admixture of contraries; and na-
ture mingling together these two kinds of
juices, difficult of coction by reason of most op-
posite defects, and then diluting them with a
large quantity of warm blood (for we see that
the quantity returned from the spleen must be
very large when we contemplate the size of its
arteries), they are brought to the porta of the
liver in a state of higher preparation; the de-
fects of either extreme are supplied and com-
pensated by this arrangement of the veins.
CHAPTER 17. The motion and circulation of the
blood are confirmed from the particulars apparent
in the structure of the heart, and from those things
winch dissection unfolds
I do not find the heart as a distinct and separate
part in all animals; some, indeed, such as the
zoophytes, have no heart; this is because these
animals are coldest, of no great bulk, of soft tex-
ture or of a certain uniform sameness or sim-
plicity of structure; among the number I may
instance grubs and earthworms, and those that
are engendered of putrefaction and do not pre-
serve their species. These have no heart, as not
requiring any impeller of nourishment into the
extreme parts; for they have bodies which are
connate and homogeneous, and without limbs;
so that by the contraction and relaxation of the
whole body they assume and expel, move and
remove the aliment. Oysters, mussels, sponges,
and the whole genus of zoophytes or plant-ani-
mals have no heart; for the whole body is used
as a heart, or the whole animal is a heart. In a
great number of animals, almost the whole tribe
of insects, we cannot see distinctly by reason of
the smallness of the body; still in bees, flies,
hornets, and the like, we can perceive with
the help of a magnifying glass something pul-
sating; in pediculi, also, the same thing may be
seen, and as the body is transparent, the passage
of the food through the intestines, like a black
spot or stain, may be perceived by the aid of
the same magnifying glass.
In some of the bloodless and colder animals,
further, as in snails, whelks, shrimps, and shell-
fish, there is a part which pulsates— a kind of
vesicle or auricle without a heart — slowly in-
deed, and not to be perceived save in the warmer
season of the year. In these creatures this part
is so contrived that it shall pulsate, as there is
here a necessity for some impulse to distribute
the nutritive fluid, by reason of the variety of
organic parts, or of the density of the substance ;
but the pulsations occur infrequently, and
sometimes in consequence of the cold not at all,
an arrangement the best adapted to them as
being of a doubtful nature, so that sometimes
they appear to live, sometimes to die; some-
times they show the vitality of an animal, some-
times of a vegetable. This seems also to be the
case with the insects which conceal themselves
in winter, and lie, as it were, defunct, or merely
manifesting a kind of vegetative existence. But
whether the same thing happens in the case of
certain animals that have red blood, such as
frogs, tortoises, serpents, swallows, may be
made a question without any kind of impro-
priety.
In all the larger and warmer, because blooded
animals, there was need of an impeller of the
nutritive fluid, and that perchance possessing a
considerable amount of power. In fishes, ser-
pents, lizards, tortoises, frogs, and others of the
same kind there is a heart present, furnished
with both an auricle and a ventricle, whence it
is perfectly true, as Aristotle has observed,1
that no blooded animal is without a heart, by
the impelling power of which the nutritive
fluid is forced, both with greater vigour and
rapidity to a greater distance; it is not merely
agitated by an auricle as it is in lower forms.
And then in regard to animals that are yet
1 On the Parts of Animals ', in.
3oo
WILLIAM HARVEY
larger, warmer, and more perfect, as they abound
in blood, which is ever hotter and more spiritu-
ous, and possess bodies of greater size and con-
sistency, they require a larger, stronger, and
more fleshy heart, in order that the nutritive
fluid may be propelled with yet greater force
and celerity. And further, inasmuch as the more
perfect animals require a still more perfect nu-
trition, and a larger supply of native heat, in
order that the aliment may be thoroughly con-
cocted and acquire the last degree of perfection,
they required both lungs and a second ven-
tricle, which should force the nutritive fluid
through them.
Every animal that has lungs has, therefore,
two ventricles to its heart, one right, another
left; and wherever there is a right, there also is
there a left ventricle; but the contrary of this
does not hold good: where there is a left there
is not always a right ventricle, The left ven-
tricle I call that which is distinct in office, not
in place from the other, that one namely which
distributes the blood to the body at large, not
to the lungs only. Hence the left ventricle seems
to form the principal part of the heart; situated
in the middle, more strongly marked, and con-
structed with greater care, the heart seems
formed for the sake of the left ventricle, and
the right but to minister to it; for the right
neither reaches to the apex of the heart, nor is
it nearly of such strength, being three times
thinner in its walls, and in some sort jointed on
to the left (as Aristotle says) ; though indeed it
is of greater capacity, inasmuch as it has not
only to supply material to the left ventricle,
but likewise to furnish aliment to the lungs.
It is to be observed, however, that all this is
otherwise in the embryo, where there is not
such a difference between the two ventricles;
but as in a double nut, they are nearly equal in
all respects, the apex of the right reaching to
the apex of the left, so that the heart presents
itself as a sort of double-pointed cone. And this
is so, because in the foetus, as already said, whilst
the blood is not passing through the lungs from
the right to the left cavities of the heart, but
flowing by the foramen ovale and ductus ar-
teriosus, directly from the vena cava into the
aorta, whence it is distributed to the whole
body, both ventricles have in fact the same
office to perform, whence their equality of con-
stitution. It is only when the lungs come to be
used, and it is requisite that the passages indi-
cated should be blocked up, that the difference
in point of strength and other things between
the two ventricles begins to be apparent : in the
altered circumstances the right has only to
throw the blood through the lungs, whilst the
left has to impel it through the whole body.
There are further within the heart numerous
braces, so to speak, fleshy columns and fibrous
bands, which Aristotle, in his third book on
Respiration, and the Parts of Animals, entitles
nerves. These are variously extended, and are
either distinct or contained in grooves in the
walls and partition, where they occasion nu-
merous pits or depressions. They constitute a
kind of small muscles, which are superadded
and supplementary to the heart, assisting it to
execute a more powerful and perfect contrac
tion, and so proving subservient to the com
plete expulsion of the blood. They are in some
sort like the elaborate and artful arrangement
of ropes in a ship, bracing the heart on ever)
side as it contracts, and so enabling it more ef
fectually and forcibly to expel the charge ol
blood from its ventricles. This much is plain
at all events, that some animals have therr
strongly marked, others have them less so; and
in all that have them, they are more numerous
and stronger in the left than in the right ven-
tricle; and whilst some have them in the left,
there are yet none present in the right ventri-
cle. In the human subject, again, these fleshy
columns and braces are more numerous in the
left than in the right ventricle, and they are
more abundant in the ventricles than in the
auricles; occasionally, indeed, in the auricles
there appear to be none present whatsoever. In
large, more muscular and hardier bodies, as of
countrymen, they are numerous; in more slen-
der frames and in females they are fewer.
In those animals in which the ventricles of
the heart are smooth within, and entirely with-
out fibres or muscular bands, or anything like
foveae, as in almost all the smaller birds, the
partridge and the common fowl, serpents, frogs,
tortoises, and also fishes, for the major part,
there are no chordae tendineae, nor bundles of
fibres, neither are there any tricuspid valves in
the ventricles.
Some animals have the right ventricle smooth
internally, but the left provided with fibrous
bands, such as the goose, swan, and larger birds;
and the reason here is still the same as elsewhere :
as the lungs are spongy, and loose, and soft, no
great amount of force is required to force the
blood through them; hence the right ventricle
is either without the bundles in question, or
they are fewer and weaker, not so fleshy or like
muscles; those of the left ventricle, however,
are both stronger and more numerous, more
MOTION OF THE HEART
301
fleshy and muscular, because the left ventricle
requires to be stronger, inasmuch as the blood
which it propels has to be driven through the
whole body. And this, too, is the reason why
the left ventricle occupies the middle of the
heart, and has parietes three times thicker and
stronger than those of the right. Hence all ani-
mals— and among men it is not otherwise —
that are endowed with particularly strong
frames, and that have large and fleshy limbs at
a great distance from the heart, have this cen-
tral organ of greater thickness, strength, and
muscularity. And this is both obvious and neces-
sary. Those, on the contrary, that are of softer
and more slender make have the heart more
flaccid, softer, and internally either sparely or
not at all fibrous. Consider further the use of
the several valves, which are all so arranged
that the blood once received into the ventricles
of the heart shall never regurgitate, once forced
into the pulmonary artery and aorta shall not
flow back upon the ventricles. When the valves
are raised and brought together they form a
three-cornered line, such as is left by the bite
of a leech; and the more they are forced, the
more firmly do they oppose the passage of the
blood. The tricuspid valves are placed, like
gate-keepers, at the entrance into the ventri-
cles from the venae cavae and pulmonary veins,
lest the blood when most forcibly impelled
should flow back: and it is for this reason that
they are not found in all animals; neither do
they appear to have been constructed with
equal care in all the animals in which they are
found; in some they are more accurately fitted,
in others more remissly or carelessly contrived,
and always with a view to their being closed
under a greater or a slighter force of the ven-
tricle. In the left ventricle, therefore, and in
order that the occlusion may be the more per-
fect against the greater impulse, there are only
two valves, like a mitre, and produced into an
elongated cone, so that they come together and
touch to their middle; a circumstance which
perhaps led Aristotle into the error of supposing
this ventricle to be double, the division taking
place transversely. For the same reason, indeed,
and that the blood may not regurgitate upon
the pulmonary veins, and thus the force of the
ventricle in propelling the blood through the
system at large come to be neutralized, it is
that these mitral valves excel those of the right
ventricle in size and strength, and exactness of
closing. Hence, too, it is essential that there can
be no heart without a ventricle, since this must
be the source and storehouse of the blood. The
same law does not hold good in reference to the
brain. For almost no genus of birds has a ven-
tricle in the brain, as is obvious in the goose and
swan, the brains of which nearly equal that of a
rabbit in size; now rabbits have ventricles in
the brain, whilst the goose has none. In like
manner, wherever the heart has a single ven-
tricle, there is an auricle appended, flaccid,
membranous, hollow, filled with blood; and
where there are two ventricles, there are like-
wise two auricles. On the other hand, however,
some animals have an auricle without any ven-
tricle; or at all events they have a sac analogous
to an auricle; or the vein itself, dilated at a par-
ticular part, performs pulsations, as is seen in
hornets, bees, and other insects, which certain
experiments of my own enable me to demon-
strate have not only a pulse, but a respiration
in that part which is called the tail, whence it is
that this part is elongated and contracted now
more rarely, now more frequently, as the crea-
ture appears to be blown and to require a larger
quantity of air. But of these things, more in our
Treatise on Respiration.
It is in like manner evident that the auricles
pulsate, contract, as I have said before, and
throw the blood into the ventricles; so that
wherever there is a ventricle an auricle is nec-
essary, not merely that it may serve, according
to the general belief, as a source and magazine
for the blood: for what were the use of its pul-
sations had it nothing to do save to contain?
No; the auricles are prime movers of the blood,
especially the right auricle, which is "the first
to live, the last to die"; as already said; whence
they are subservient to sending the blood into
the ventricle, which, contracting incontinently,
more readily and forcibly expels the blood al-
ready in motion; just as the ball-player can
strike the ball more forcibly and farther if he
takes it on the rebound than if he simply threw
it. Moreover, and contrary to the general opin-
ion, since neither the heart nor anything else
can dilate or distend itself so as to draw aught
into its cavity during the diastole, unless, like a
sponge, it has been first compressed, and as it is
returning to its primary condition; but in ani-
mals all local motion proceeds from, and has its
original in the contraction of some part: it is
consequently by the contraction of the auricles
that the blood is thrown into the ventricles, as
I have already shown, and from thence, by the
contraction of the ventricles, it is propelled and
distributed. Which truth concerning local mo-
tions, and how the immediate moving organ in
every motion of an animal primarily endowed
302
WILLIAM HARVEY
with a motive spirit (as Aristotle has it),1 is
contractile; and in what way the word vtvpov
is derived from veva), nuto, contraho; and how
Aristotle was acquainted with the muscles, and
did not unadvisedly refer all motion in animals
to the nerves, or to the contractile element,
and therefore called those little bands in the
heart nerves— all this, if I am permitted to pro-
ceed in my purpose of making a particular dem-
onstration of the organs of motion in animals
from observations in my possession, I trust I
dhall be able to make sufficiently plain.
But that we may go on with the subject we
nave in hand, viz., the use of the auricles in
filling the ventricles: we should expect that the
more dense and compact the heart, the thicker
its parietes, the stronger and more muscular
must be the auricle to force and fill it, and vice
versa. Now this is actually so: in some the auricle
presents itself as a sanguinolent vesicle, as a thin
membrane containing blood, as in fishes, in
which the sac that stands in lieu of the auricle,
is of such delicacy and ample capacity, that it
seems to be suspended or to float above the
heart; in those fishes in which the sac is some-
what more fleshy, as in the carp, barbel, tench,
and others, it bears a wonderful and strong re-
semblance to the lungs.
In some men of sturdier frame and stouter
make, the right auricle is so strong, and so curi-
ously constructed within of bands and variously
interlacing fibres, that it seems to equal the
ventricle of the heart in other subjects; and I
must say that I am astonished to find such di-
versity in this particular in different individu-
als. It is to be observed, however, that in the
foetus the auricles are out of all proportion large,
which is because they are present before the
heart makes its appearance or suffices for its
office even when it has appeared, and they,
therefore, have, as it were, the duty of the
whole heart committed to them, as has already
been demonstrated. But what I have observed
in the formation of the foetus as before remarked
(and Aristotle had already confirmed all in
studying the incubated egg) throws the greatest
light and likelihood upon the point. Whilst the
foetus is yet in the guise of a soft worm, or, as
is commonly said, in the milk, there is a mere
bloody point or pulsating vesicle, a portion ap-
parently of the umbilical vein, dilated at its
commencement or base; by and by, when the
outline of the foetus is distinctly indicated, and
it begins to have greater bodily consistence, the
vesicle in question having become more fleshy
1 In the book, DC spiritu, and elsewhere.
and stronger, and changed its position, passes
into the auricles, over or upon which the body
of the heart begins to sprout, though as yet it
apparently performs no duty; but when the
foetus is farther advanced, when the bones can
be distinguished from the soft parts, and move-
ments take place, then it has also a heart inter-
nately which pulsates, and, as I have said,
throws blood by either ventricle from the vena
cava into the arteries.
Thus nature, ever perfect and divine, doing
nothing in vain, has neither given a heart where
it was not required, nor produced it before its
office had become necessary; but by the same
stages in the development of every animal,
passing through the constitutions of all, as I
may say (ovum, worm, foetus), it acquires per-
fection in each. These points will be found
elsewhere confirmed by numerous observations
on the formation of the foetus.
Finally, it was not without good grounds
that Hippocrates, in his book, De corde, entitles
it a muscle; as its action is the same, so is its
function, viz., to contract and move something
else, in this case, the charge of blood.
Further, as in muscles at large, so can we in-
fer the action and use of the heart from the
arrangement of its fibres and its general struc-
ture. All anatomists admit with Galen that the
body of the heart is made up of various courses
of fibres running straight, obliquely, and trans-
versely, with reference to one another; but in a
heart which has been boiled the arrangement
of the fibres is seen to be different: all the fibres
in the parietes and septum are circular, as in the
sphincters; those, again, which are in the co-
lumnae extend lengthwise, and are oblique longi-
tudinally; and so it comes to pass that, when all
the fibres contract simultaneously, the apex of
the cone is pulled towards its base by the co-
lumnae, the walls are drawn circularly together
into a globe, the whole heart in short is con-
tracted, and the ventricles narrowed; it is there-
fore impossible not to perceive that, as the ac-
tion of the organ is so plainly contraction, its
function is to propel the blood into the arteries.
Nor are we the less to agree with Aristotle in
regard to the sovereignty of the heart; nor are
we to inquire whether it receives sense and mo-
tion from the brain? whether blood from the
liver? whether it be the origin of the veins and
of the blood ? and more of the same description.
They who affirm these propositions against
Aristotle, overlook, or do not rightly under-
stand the principal argument, to the effect that
the heart is the first part which exists, and that
MOTION OF THE HEART
3<>3
it contains within itself blood, life, sensation,
motion, before either the brain or the liver
were in being, or had appeared distinctly, or, at
all events, before they could perform any func-
tion. The heart, ready furnished with its proper
organs of motion, like a kind of internal crea-
ture, is of a date anterior to the body: first
formed, nature willed that it should afterwards
fashion, nourish, preserve, complete the entire
animal, as its work and dwelling place: the
heart, like the prince in a kingdom, in whose
hands lie the chief and highest authority, rules
over all; it is the original and foundation from
which all power is derived, on which all power
depends in the animal body.
And many things having reference to the
arteries further illustrate and confirm this truth.
Why does not the arteria venosa pulsate, seeing
that it is numbered among the arteries? Or
wherefore is there a pulse in the vena arteriosa?
Because the pulse of the arteries is derived from
the impulse of the blood. Why does an artery
differ so much from a vein in the thickness and
strength of its coats? Because it sustains the
shock of the impelling heart and streaming
blood. Hence, as perfect nature does nothing in
vain, and suffices under all circumstances, we
find that the nearer the arteries are to the heart,
the more do they differ from the veins in struc-
ture; here they are both stronger and more lig-
amentous, whilst in extreme parts of the body,
such as the feet and hands, the brain, the mes-
entery, and the testicles, the two orders of ves-
sels are so much alike that it is impossible to dis-
tinguish between them with the eye. Now this
is for the following very sufficient reasons: for
the more remote vessels are from the heart,
with so much the less force are they impinged
upon by the stroke of the heart, which is broken
by the great distance at which it is given. Add
to this, that the impulse of the heart exerted
upon the mass of blood, which must needs fill
the trunks and branches of the arteries, is di-
verted, divided, as it were, and diminished at
every subdivision; so that the ultimate capil-
lary divisions of the arteries look like veins, and
this not merely in constitution but in function;
for they have either no perceptible pulse, or
they rarely exhibit one, and never save where
the heart beats more violently than wont, or at
a part where the minute vessel is more dilated
or open than elsewhere. Hence it happens that
at times we are aware of a pulse in the teeth, in
inflammatory tumours, and in the fingers; at
another time we feel nothing of the sort. Hence,
too, by this single symptom I have ascertained
for certain that young persons, whose pulses are
naturally rapid, were labouring under fever; in
like manner, on compressing the fingers in youth-
ful and delicate subjects during a febrile par-
oxysm, I have readily perceived the pulse there.
On the other hand, when the heart pulsates
more languidly, it is often impossible to feel
the pulse not merely in the fingers, but at the
wrist, and even at the temple; this is the case
in persons afflicted with lipothymise and as-
phyxia, and hysterical symptoms, as also in
persons of very weak constitution and in the
moribund.
And here surgeons are to be advised that,
when the blood escapes with force in the ampu-
tation of limbs, in the removal of tumours, and
in wounds, it constantly comes from an artery;
not always per saltum, however, because the
smaller arteries do not pulsate, especially if a
tourniquet has been applied.
And then the reason is the same wherefore
the pulmonary artery has not only the struc-
ture of an artery, but wherefore it does not
differ so widely in the thickness of its tunics
from the veins as the aorta: the aorta sustains a
more powerful shock from the left ventricle
than the pulmonary artery does from the right;
and the tunics of this last vessel are thinner and
softer than those of the aorta in the same pro-
portion as the walls of the right ventricle of the
heart are weaker and thinner than those of the
left ventricle; and in like manner, in the same
degree in which the lungs are softer and laxer
in structure than the flesh and other constitu-
ents of the body at large, do the tunics of the
branches of the pulmonary artery differ from
the tunics of the vessels derived from the aorta.
And the same proportion in these several par-
ticulars is universally preserved. The more mus-
cular and powerful men are, the firmer their
flesh, the stronger, thicker, denser, and more
fibrous their heart, in the same proportion are
the auricles and arteries in all respects thicker,
closer, and stronger. And again, and on the
other hand, in those animals the ventricles of
whose heart are smooth within, without villi or
valves, and the walls of which are thinner, as in
fishes, serpents, birds, and very many genera of
animals, in all of them the arteries differ little
or nothing in the thickness of their coats from
the veins.
Further, the reason why the lungs have such
ample vessels, both arteries and veins (for the
capacity of the pulmonary veins exceeds that
of both the crural and jugular vessels), and why
they contain so large a quantity of blood, as by
304
WILLIAM HARVEY
experience and ocular inspection we know they
do, admonished of the fact indeed by Aristotle,
and not led into error by the appearances found
in animals which have been bled to death, is,
because the blood has its fountain, and store-
house, and the workshop of its last perfection
in the heart and lungs. Why, in the same way
we find in the course of our anatomical dissec-
tions the arteria venosa and left ventricle so
full of blood, of the same black colour and clot-
ted character, too, as that with which the right
ventricle and pulmonary artery are filled, in-
asmuch as the blood is incessantly passing from
one side of the heart to the other through the
lungs. Wherefore, in fine, the pulmonary artery
or vena arteriosa has the constitution of an ar-
tery, and the pulmonary veins or arteriae veno-
sae have the structure of veins; because, in
sooth, in function and constitution, and every-
thing else, the first is an artery, the others are
veins, in opposition to what is commonly be-
lieved; and why the pulmonary artery has so
large an orifice, because it transports much
more blood than is requisite for the nutrition
of the lungs.
All these appearances, and many others, to be
noted in the course of dissection, if rightly
weighed, seem clearly to illustrate and fully to
confirm the truth contended for throughout
these pages, and at the same time to stand in
opposition to the vulgar opinion; for it would
be very difficult to explain in any other way
to what purpose all is constructed and arranged
as we have seen it to be.
The First Anatomical Disquisition on the Circu-
lation of the Blood, Addressed to John Riolan
SOME few months ago there appeared a small
anatomical and pathological work from the pen
of the celebrated Riolanus, for which, as sent
to me by the author himself, I return him my
grateful thanks.1 1 also congratulate this author
on the highly laudable undertaking in which he
has engaged. To demonstrate the seats of all
diseases is a task that can only be achieved un-
der favour of the highest abilities; for surely he
enters on a difficult province who proposes to
bring under the cognizance of the eyes those
diseases which almost escape the keenest un-
derstanding. But such efforts become the prince
of anatomists; for there is no science which does
not spring from preexisting knowledge, and no
certain and definite idea which has not derived
its origin from the senses. Induced therefore by
the subject itself, and the example of so dis-
tinguished an individual, which makes me think
lightly of the labour, I also intend putting to
press my Medical Anatomy, or Anatomy in its
Application to Medicine. Not with the purpose,
like Riolanus, of indicating the seats of diseases
from the bodies of healthy subjects, and dis-
cussing the several diseases that make their ap-
pearance there, according to the views which
others have entertained of them; but that I may
relate from the many dissections I have made of
the bodies of persons diseased, worn out by seri-
ous and strange affections, how and in what
way the internal organs were changed in their
situation, size, structure, figure, consistency,
and other sensible qualities, from their natural
forms and appearances, such as they are usually
described by anatomists; and in what various
and remarkable ways they were affected. For
even as the dissection of healthy and well-con-
stituted bodies contributes essentially to the
advancement of philosophy and sound physi-
ology, so does the inspection of diseased and ca-
chectic subjects powerfully assist philosophical
pathology. And, indeed, the physiological
1 Enchcindtum anatomicum ct pathologicutn, 12010,
Parisiis, 1648.
consideration of the things which are according
to nature is to be first undertaken by medical
men; since that which is in conformity with
nature is right, and serves as a rule both to it-
self and to that which is amiss; by the light it
sheds, too, aberrations and affections against
nature are defined; pathology then stands out
more clearly; and from pathology the use and
art of healing, as well as occasions for the dis-
covery of many new remedies, are perceived.
Nor could anyone readily imagine how exten-
sively internal organs are altered in diseases,
especially chronic diseases, and what monstrosi-
ties among internal parts these diseases engen-
der. So that I venture to say, that the examina-
tion of a single body of one who has died of
tabes or some other disease of long standing, or
poisonous nature, is of more service to medicine
than the dissection of the bodies of ten men
who have been hanged.
I would not have it supposed by this that I in
any way disapprove of the purpose of Riolanus,
that learned and skilful anatomist; on the con-
trary, I think it deserving of the highest praise,
as likely to be extremely useful to medicine, in-
asmuch as it illustrates the physiological branch
of this science; but I have thought that it would
scarcely turn out less profitable to the art of
healing, did I place before the eyes of my read-
ers not only the places, but the affections of
these places, illustrating them as I proceed with
observations, and recording the results of my
experience derived from my numerous dissec-
tions.
But it is imperative on me first to dispose of
those observations contained in the work re-
ferred to, which bear upon the circulation of
the blood as discovered by me, and which seem
to require especial notice at my hands. For the
judgment of such a man, who is indeed the
prince and leader of all the anatomists of the
present age, in such a matter, is not to be
lightly esteemed, but is rather to be held of
greater weight and authority, either for praise
3°5
WILLIAM HARVEY
or blame, than the commendations or censure
of all the world besides.
Riolanus, then, admits our motion of the
blood in animals,1 and falls in with our conclu-
sions in regard to the circulation; yet not en-
tirely and avowedly; for he says2 that the blood
contained in the vena portae does not circulate
like that in the vena cava; and again he states3
that there is some blood which circulates, and
that the circulatory vessels are the aorta and
vena cava; but then he denies that the continu-
ations of these trunks have any circulation, "be-
cause the blood is effused into all the parts of
the second and third regions, where it remains
for purposes of nutrition; nor does it return to
any greater-vessels, unless forcibly drawn back
when there is a great lack of blood in the main
channels, or driven by a fit of passion when it
flows to the greater circulatory vessels"; and
shortly afterwards: "thus, as the blood of the
veins naturally ascends incessantly or returns to
the heart, so the blood of the arteries descends
or departs from the heart; still, if the smaller
veins of the arms and legs be empty, the blood
filling the empty channels in succession, may
descend in the veins, as I have clearly shown,"
he says, "against Harvey and Walaeus." And as
the authority of Galen and daily experience
confirm the anastomoses of the arteries and
veins, and the necessity of the circulation of
the blood, "you perceive," he continues, "how
the circulation is effected, without any pertur-
bation or confusion of fluids and the destruc-
tion of the ancient system of medicine."
These words explain the motives by which
this illustrious anatomist was actuated when he
was led partly to admit, partly to deny the cir-
culation of the blood; and why he only ven-
tures on an undecided and inconclusive opinion
of the subject; his fear is lest it destroy the an-
cient medicine. Not yielding implicitly to the'
truth, which it appears he could not help see-
ing, but rather guided by caution, he fears
speaking plainly out, lest he offend the ancient
physic, or perhaps seem to retract the physio-
logical doctrines he supports in his Anthropology.
The circulation of the blood does not shake, but
much rather confirms the ancient medicine;
though it runs counter to the physiology of
physicians, and their speculations upon natural
subjects, and opposes the anatomical doctrine
of the use and action of the heart and lungs,
and rest of the viscera. That this is so shall
1 Enchiridion, Book in, chap. 8.
* Ibid., Book n, chap. 21.
" "" d., Book in, chap. 8.
readily be made to appear, both from his own
words and avowal, and partly also from what I
shall supply; viz., that the whole of the blood,
wherever it be in the living body, moves and
changes its place, not merely that which is in
the larger vessels and their continuations, but
that also which is in their minute subdivisions,
and which is contained in the pores or inter-
stices of every part; that it flows from and back
to the heart ceaselessly and without pause, and
could not pause for ever so short a time without
detriment, although I admit that occasionally,
and in some places, its motion is quicker or
slower.4
In the first place, then, our learned anatomist
only denies that the contents of the branches in
continuation of the vena portae circulate; but
he could neither oppose nor deny this, did he
not conceal from himself the force of his own
arguments; for he says in his Third Book, chap-
ter 8 ...., "If the heart at each pulsation admits a
drop of blood which it throws into the aorta,
and in the course of an hour makes two thou-
sand beats, it is a necessary consequence that
the quantity of blood transmitted must be
great." He is further forced to admit as much in
reference to the mesentery, when he sees that
far more than single drops of blood are sent
into the cceliac and mesenteric arteries at each
pulsation; so that there must either be some
outlet for the fluid, of magnitude commen-
surate with its quantity, or the branches of the
vena portae must give way. Nor can the explan-
ation that is had recourse to with a view of
meeting the difficulty, viz., that the blood of
the mesentery ebbs and flows by the same chan-
nels, after the manner of Euripus, be received
as either probable or possible. Neither can the
reflux from the mesentery be effected by those
passages and that system of translation, by
which he will have it to disgorge itself into the
aorta; this were against the force of the existing
current, and by a contrary motion; nor can any-
thing like pause or alternation be admitted,
where there is very certainly an incessant in-
flux: the blood sent into the mesentery must as
inevitably go elsewhere as that which is poured
into the heart. And this is obvious; were it other-
wise, indeed, everything like a circulation
might be overturned upon the same showing
and by the same subterfuge; it might just as
well be said that the blood contained in the left
ventricle of the heart is propelled into the aorta
during the systole, and flows back to it during
4 See Chapter 3, of the Disquisition on the Motion of
the Heart and Blood.
CIRCULATION OF THE BLOOD
307
the diastole, the aorta disgorging itself into the
ventricle, precisely as the ventricle has dis-
gorged itself into the aorta. There would thus
be circulation neither in the heart nor in the
mesentery, but an alternate flux and reflux —
a useless labour, as it seems. If, therefore, and
for the reason assigned and approved by him, a
circulation through the heart be argued for as a
thing necessary, the argument has precisely the
same force when applied to the mesentery: if
there be no circulation in the mesentery, nei-
ther is there any in the heart; for both affirma-
tions, this in reference to the heart, that in ref-
erence to the mesentery, merely changing the
words, stand or fall together, by force of the
very same arguments.
He says: "The sigmoid valves prevent regur-
gitation into the heart; but there are no valves
in the mesentery." To this I reply, that the
thing is not so; for there is a valve in the splenic
vein, and sometimes also in other veins. And
besides, valves are not met with universally in
veins; there are few or none in the deep-seated
veins of the extremities, but many in the sub-
cutaneous branches. For where the blood is
flowing naturally from smaller into greater
branches, into which it is disposed to enter, the
pressure of the circumjacent muscles is enough,
and more than enough to prevent all retrograde
movement, and it is forced on where the way
lies open; in such circumstances, what use were
there for valves ? But the quantity of blood that
is forced into the mesentery by each stroke of
the heart, may be estimated in the same way as
you estimate the quantity impelled into the
hand when you bind a ligature with medium
tightness about the wrist: if in so many beats
the vessels of the hand become distended, and
the whole extremity swells, you will find that
much more than a single drop of blood has en-
tered with each pulse, and which cannot re-
turn, but must remain to fill the hand and in-
crease its size. But analogy permits us to say
that the same thing takes place in reference to
the mesentery and its vessels, in an equal de-
gree at least, if not in a greater degree, seeing
that the vessels of the mesentery are consider-
ably larger than those of the carpus. And if any-
one will but think on the difficulty that is ex-
perienced with all the aid supplied by com-
presses, bandages, and a multiplied apparatus,
in restraining the flow of blood from the small-
est artery when wounded, with what force it
overcomes all obstacles and soaks through the
whole apparatus, he will scarcely, I imagine,
think it likely that there can be any retrograde
motion against such an impulse and influx of
blood, any retrograde force to meet and over-
come a direct force of such power. Turning
over these things in his mind, I say, no one wiU
ever be brought to believe that the blood from
the branches of the vena portae can possibly
make its way by the same channels against an
influx by the artery of such impetuosity and
force, and so unload the mesentery.
Moreover, if the learned anatomist does not
think that the blood is moved and changed by
a circular motion, but that the same fluid al-
ways stagnates in the channels of the mesentery,
he appears to suppose that there are two descrip-
tions of blood, serving different uses and ends;
that the blood of the vena portae, and that of
the vena cava are dissimilar in constitution,
seeing that the one requires a circulation for its
preservation, the other requires nothing of the
kind; which neither appears on the face of the
thing, nor is its truth demonstrated by him.
Our author then refers to "A fourth order of
mesenteric vessels, the lacteal vessels, discov-
ered by Asellius";1 and having mentioned
these, he seems to infer that they extract all the
nutriment from the intestines, and transfer this
to the liver, the workshop of the blood, whence,
having been concocted and changed into blood
(so he says in his Third Boo\, chapter 8), the
blood is transferred from the liver to the right
ventricle of the heart. "Which things pre-
mised," he continues, "all the difficulties
which were formerly experienced in regard to
the distribution of the chyle and blood by the
same channel come to an end; for the lacteal
veins carry the chyle to the liver, and as these
canals are distinct, so may they be severally ob-
structed."2 But truly I would here ask: how
this milky fluid can be poured into and pass
through the liver, and how from thence gain
the vena cava and the ventricle of the heart ?
when our author denies that the blood of the
vena portae passes through the liver, and that
so a circulation is established. I pause for a
reply. I would fain know how such a thing can
be shown to be probable; especially when the
blood appears to be both more spirituous or
subtile and penetrating than the chyle or milk
contained in these lacteal vessels, and is further
impelled by the pulsations of the arteries that
it may find a passage by other channels.
Our learned author mentions a certain tract
of his on the Circulation of the Blood: I wish I
could obtain a sight of it; perhaps I might re-
1 Enchiridion^ Book n, chap. 18.
308
WILLIAM HARVEY
tract. But had the learned writer been so dis-
posed, I do not see but that having admitted the
circular motion of the blood,1 all the difficulties
which were formerly felt in connexion with the
distribution of the chyle and the blood by the
same channels are brought to an equally satis-
factory solution; so much so indeed that there
would be no necessity for inquiring after or
laying down any separate vessels for the chyle.
Even as the umbilical veins absorb the nutri-
tive juices from the fluids of the egg and trans-
port them for the nutrition and growth of the
chick, in its embryo state, so do the meseraic
veins suck up the chyle from the intestines and
transfer it to the liver; and why should we not
maintain that they perform the same office in
the adult? For all the mooted difficulties van-
ish when we cease to suppose two contrary mo-
tions in the same vessels, and admit but one
and the same continuous motion in the mesen-
teric vessels from the intestines to the liver.
I shall elsewhere state my views of the lacteal
veins when I treat of the milk found in dif-
ferent parts of new-born animals, especially of
the human subject; for it is met with in the mes-
entery and all its glands, in the thymus, in the
axillae, also in the breasts of infants. This milk
the midwifes are in the habit of pressing out, for
the health, as they believe, of the infants. But
it has pleased the learned Riolanus, not only to
take away circulation from the blood contained
in the mesentery ; he affirms that neither do the
vessels in continuation of the vena cava, nor
the arteries, nor any of the parts of the second
and third regions, admit of circulation, so that
he entitles and enumerates as circulating vessels
the vena cava and aorta only. For this he ap-
pears to me to give a very indifferent reason:
'The blood," he says, "effused into all the parts
of the second and third regions, remains there
for their nutrition; nor does it return to the
great vessels, unless forcibly drawn back by an
extreme dearth of blood in the great vessels,
nor, unless carried by an impulse, does it flow to
the circulatory vessels."2
That so much of the blood must remain as is
appropriated to the nutrition of the tissues, is
matter of necessity ; for it cannot nourish unless
it be assimilated and become coherent, and
form substance in lieu of that which is lost; but
that the whole of the blood which flows into a
1 Enchiridion, Book in, chap. 8: "The blood incessantly
and naturally ascends or flows back to the heart in the
veins, as in the arteries it descends or departs from the
heart."
part should there remain, in order that so small
a portion should undergo transformation, is no-
wise necessary; for no part uses so much blood
for its nutrition as is contained in its arteries,
veins, and interstices. Nor because the blood is
continually coming and going is it necessary to
suppose that it leaves nothing for nutriment be-
hind it. Consequently it is by no means neces-
sary that the whole remain in order that nutri-
tion be effected. But our learned author, in the
same book, where he affirms so much, appears
almost everywhere else to assert the contrary.
In that paragraph especially where he describes
the circulation in the brain, he says: "And the
brain by means of the circulation sends back
blood to the heart, and thus refrigerates the
organ." And in the same way are all the more
remote parts said to refrigerate the heart; thus
in fevers, when the praecordia are scorched and
burn with febrile heat, patients baring their
limbs and casting off the bedclothes, seek to
cool their heart; and the blood generally, tem-
pered and cooled down, as our learned author
states it to be with reference to the brain in
particular, returns by the veins and refriger-
ates the heart. Our author, therefore, appears
to insinuate a certain necessity for a circula-
tion from every part, as well as from the brain,
in opposition to what he had before said in very
precise terms. But then he cautiously and am-
biguously asserts, that the blood does not re-
turn from the parts composing the second and
third regions, unless, as he says, it is drawn by
force, and through a signal deficiency of blood
in the larger vessels, &c., which is most true if
these words be rightly understood; for by the
larger vessels, in which the deficiency is said to
cause the reflux, I think he must be held to
mean the veins not the arteries; for the arteries
are never emptied, save into the veins or in-
terstices of parts, but are incessantly filled by
the strokes of the heart; but in the vena cava
and other returning channels, in which the
blood glides rapidly on, hastening to the heart,
there would speedily be a great deficiency of
blood did not every part incessantly restore the
blood that is incessantly poured into it. Add to
this, that by the impulse of the blood which is
forced with each stroke into every part of the
second and third regions, that which is con-
tained in the pores or interstices is urged into
the smaller veins, from which it passes into
larger vessels, its motion assisted besides by the
motion and pressure of circumjacent parts; for
from every containing thing compressed and
const ringed, contained matters arc forced out.
CIRCULATION OF THE BLOOD
309
And thus it is that by the motions of the mus-
cles and extremities, the blood contained in the
minor vessels is forced onwards and delivered
into the larger trunks. But that the blood is
incessantly driven from the arteries into every
part of the body, there gives a pulse and never
flows back in these channels, cannot be doubted,
if it be admitted that with each pulse of the
heart all the arteries are simultaneously dis-
tended by the blood sent into them; and as our
learned author himself allows that the diastole
of the arteries is occasioned by the systole of
the heart, and that the blood once out of the
heart can never get back into the ventricles by
reason of the opposing valves; if I say, our
learned author believes that these things are so,
it will be as manifestly true with regard to the
force and impulse by which the blood con-
tained in the vessels is propelled into every part
of every region of the body. For wheresoever
the arteries pulsate, so far must the impulse and
influx extend, and therefore is the impulse felt
in every part of each several region; for there is
a pulse everywhere, to the very points of the
ringers and under the nails, nor is there any part
of the body where the shooting pain that ac-
companies each pulse of the artery, and the ef-
fort made to effect a solution of the continuity
is not experienced when it is the seat of a phleg-
mon or furuncle.
But, further, that the blood contained in the
pores of the living tissues returns to the heart,
is manifest from what we observe in the hands
and feet. For we frequently see the hands and
feet, in young persons especially, during severe
weather, become so cold that to the touch they
feel like ice, and they are so benumbed and
stiffened that they seem scarcely to retain a
trace of sensibility or to be capable of any mo-
tion; still are they all the while surcharged with
blood, and look red or livid. Yet can the ex-
tremities be warmed in no way, save by circu-
lation; the chilled blood, which has lost its spirit
and heat, being driven out, and fresh, warm,
and vivified blood flowing in by the arteries in
its stead, which fresh blood cherishes and warms
the parts, and restores to them sense and mo-
tion; nor could the extremities be restored by
the warmth of a fire or other external heat, any
more than those of a dead body could be so re-
covered: they are only brought to life again, as
it were, by an influx of internal warmth. And
this indeed is the principal use and end of the
circulation; it is that for which the blood is sent
on its ceaseless course, and to exert its influence
continually in its circuit, to wit, that all parts
dependent on the primary innate heat may be
retained alive, in their state of vital and vege-
tative being, and apt to perform their func-
tions; whilst, to use the language of physiolo-
gists, they are sustained and actuated by the in-
flowing heat and vital spirits. Thus, by the aid
of two extremes, viz., cold and heat, is the tem-
perature of the animal body retained at its
mean. For as the air inspired tempers the too
great heat of the blood in the lungs and centre
of the body, and effects the expulsion of suffo-
cating fumes, so in its turn does the hot blood,
thrown by the arteries into all parts of the
body, cherish and nourish and keep them in
life, defending them from extinction through
the power of external cold.
It would, therefore, be in some sort unfair
and extraordinary did not every particle com-
posing the body enjoy the advantages of the
circulation and transmutation of the blood; the
ends for which the circulation was mainly es-
tablished by nature would no longer be ef-
fected. To conclude then: you see how circula-
tion may be accomplished without confusion or
admixture of humours, through the whole body,
and each of its individual parts, in the smaller
as well as in the larger vessels; and all as matter
of necessity and for the general advantage;
without circulation, indeed, there would be no
restoration of chilled and exhausted parts, no
continuance of these in life; since it is apparent
enough that the whole influence of the preserv-
ative heat comes by the arteries, and is the
work of the circulation.
It, therefore, appears to me that the learned
Riolanus speaks rather expediently than truly,
when in his Enchiridion he denies a circulation
to certain parts; it would seem as though he had
wished to please the mass, and oppose none; to
have written with such a bias rather than rigid-
ly and in behalf of the simple truth. This is also
apparent when he would have the blood to
make its way into the left ventricle through the
septum of the heart, by certain invisible anc
unknown passages, rather than through those
ample and abundantly pervious channels, the
pulmonary vessels, furnished with valves, op-
posing all reflux or regurgitation. He informs uj
that he has elsewhere discussed the reasons oj
the impossibility or inconvenience of this: ]
much desire to see his disquisition. It would be
extraordinary, indeed, were the aorta and pul
monary artery, with the same dimensions, pro
perties, and structure, not to have the same
functions. But it would be more wonderfu
still were the whole tide of the blood to reach
3io
WILLIAM HARVEY
the left ventricle by a set of inscrutable pas-
sages of the septum, a tide which, in quantity
must correspond, first to the influx from the
vena cava into the right side of the heart, and
next to the efflux from the left, both of which
require such ample conduits. But our author
has adduced these matters inconsistently, for
he has established the lungs as an emunctory
or passage from the heart;1 and he says: "The
lung is affected by the blood which passes
through it, the sordes flowing along with the
blood." And, again: "The lungs receive injury
from distempered and ill-conditioned viscera;
these deliver an impure blood to the heart,
which it cannot correct except by multiplied
circulations." In the same place, he further pro-
ceeds, whilst speaking against Galen of blood-
letting in peripneumonia and the communica-
tion of the veins: "Were it true that the blood
naturally passed from the right ventricle of the
heart to the lungs, that it might be carried into
the left ventricle and from thence into the aor-
ta; and were the circulation of the blood ad-
mitted, who does not see that in affections of
the lungs the blood would flow to them in
larger quantity and would oppress them, un-
less it were taken away, first, freely, and then in
repeated smaller quantities in order to relieve
them, which indeed was the advice of Hippo-
crates, who, in affections of the lungs takes
away blood from every part —the head, nose,
tongue, arms and feet, in order that its quan-
tity may be diminished and a diversion effected
from the lungs; he takes away blood till the
body is almost bloodless. Now admitting the
circulation, the lungs are most readily depleted
by opening a vein; but rejecting it, I do not
see how any revulsion of the blood can be ac-
complished by this means; for did it flow back
by the pulmonary artery upon the right ven-
tricle, the sigmoid valves would oppose its en-
trance, and any escape from the right ventricle
into the vena cava is prevented by the tricus-
pid valves. The blood, therefore, is soon ex-
hausted when a vein is opened in the arm or
foot, if we admit the circulation; and the opin-
ion of Fernelius is at the same time upset by
this admission, viz^ that in affections of the
lungs it is better to bleed from the right than
the left arm; because the blood cannot flow
backwards into the vena cava unless the two
barriers situated in the heart be first broken
down."
He adds yet further in the same place: "If
the circulation of the blood be admitted, and it
1 Encheiridion, Book in, chap. 6.
be acknowledged that this fluid generally passes
through the lungs, not through the middle par-
tition of the heart, a double circulation be-
comes requisite; one effected through the lungs,
in the course of which the blood quitting the
right ventricle of the heart passes through the
lungs in order that it may arrive at the left ven-
tricle; leaving the heart on the one hand, there-
fore, the blood speedily returns to it again; an-
other and longer circulation proceeding from
the left ventricle of the heart performs the cir-
cuit of the whole body by the arteries, and by
the veins returns to the right side of the heart."2
The learned anatomist might here have added
a third and extremely short circulation, viz.,
from the left to the right ventricle of the heart,
with that blood which courses through the coro-
nary arteries and veins, and by their ramifica-
tions is distributed to the body, walls, and sep-
tum of the heart.
"He who admits one circulation," proceeds
our author, "cannot repudiate the other"; and
he might, as it appears, have added, "the third."
For why should the coronary arteries of the
heart pulsate, if it were not to force on the
blood by their pulsations? and why should
there be coronary veins, the end and office of
all veins being to receive the blood brought
by the arteries, were it not to deliver and dis-
charge the blood sent into the substance of the
heart? In this consideration let it be remem-
bered that a valve is very commonly found at
the orifice of the coronary vein, as our learned
author himself admits,3 preventing all ingress,
but offering no obstacle to the egress of the
blood. It therefore seems that he cannot do
otherwise than admit this third circulation,
who acknowledges a general circulation through
the body, and that the blood also passes through
the lungs and the brain.4 Nor, indeed, can he
deny a similar circulation to every other part
of every other region. The blood flowing in
under the influence of the arterial pulse, and
returning by the veins, every particle of the
body has its circulation.
From the words of our learned writer quoted
above, consequently, his opinion may be gath-
ered both of the general circulation, and then
of the circulation through the lungs and the
several parts of the body; for he who admits the
first, manifestly cannot refuse to acknowledge
the others. How indeed could he who has re-
peatedly asserted a circulation through the
2 Ibtd.
8 Ibid., chap. 9.
4 Ibid.* Book iv, chap. 2.
CIRCULATION OF THE BLOOD
311
general system and the greater vessels, deny a
circulation in the branches continuous with
these vessels, or in the several parts of the sec-
ond and third regions ? as if all the veins, and
those he calls greater circulatory vessels, were
not enumerated by every anatomist, and by
himself, as being within the second region of
the body. Is it possible that there can be a cir-
culation which is universal, and which yet does
not extend through every part? Where he
denies it, then, he does so hesitatingly, and
vacillates between negations, giving us mere
words. Where he asserts the circulation, on the
contrary, he speaks out heartily, and gives suf-
ficient reasons, as becomes a philosopher; and
then, when he relies on this opinion in a parti-
cular instance, he delivers himself like an ex-
perienced physician and honest man, and, in
opposition to Galen and his favorite Fernelius,
advises blood-letting as the chief remedy in
dangerous diseases of the lungs.
No learned man and Christian, having doubts
in such a case, would have recommended his
experience to posterity, to the imminent risk,
and even loss of human life; neither would he
without very sufficient reasons, have repudi-
ated the authority of Galen and Fernelius,
which has usually such weight with him. What-
ever he has denied in the circulation of the
blood, therefore, whether with reference to the
mesentery or any other part, and with an eye
to the lacteal veins or the ancient system of
physic, or any other consideration, must be as-
cribed to his courtesy and modesty, and is to be
excused.
Thus far, I think, it appears plain enough,
from the very words and arguments of our
author, that there is a circulation everywhere;
that the blood, wherever it is, changes its place,
and by the veins returns to the heart; so that
our learned author seems to be of the same
opinion as myself. It would therefore be labour
in vain, did I here quote at greater length the
various reasons which I have consigned in my
work on the Motion of the Blood^ in confirma-
tion of my opinions, and which are derived
from the structure of the vessels, the position
of the valves, and other matters of experience
and observation; and this the more, as I have
not yet seen the treatise on the Circulation of
the Blood of the learned writer; nor, indeed,
have I yet met with a single argument of his, or
more than his simple negation, which would
lead me to see wherefore he should reject a cir-
culation which he admits as universal, in certain
parts, regions, and vessels.
It is true that by way of subterfuge he has
recourse to an anastomosis of the vessels on the
authority of Galen, and the evidence of daily
experience. But so distinguished a personage,
an anatomist so expert, so inquisitive, and care-
ful, should first have shown anastomoses be-
tween the larger arteries and larger veins, and
these, both obvious and ample, having mouths
in relation with such a torrent as is constituted
by the whole mass of the blood, and larger than
the capacity of the continuous branches (from
which he takes away all circulation), before he
had rejected those that are familiarly known,
that are more likely and more open; he ought
to have clearly shown us where these anasto-
moses are, and how they are fashioned, whether
they be adapted only to permit the access of
the blood into the veins, and not to allow of its
regurgitation, in the same way as we see the
ureters connected with the urinary bladder, or
in what other manner things are contrived. But
— and here I speak over boldly perhaps —
neither our learned author himself, nor Galen,
nor any experience, has ever succeeded in mak-
ing such anastomoses as he imagines, sensible to
the eye.
I have myself pursued this subject of the an-
astomosis with all the diligence I could com-
mand, and have given not a little both of time
and labour to the inquiry; but I have never suc-
ceeded in tracing any connexion between ar-
teries and veins by a direct anastomosis of their
orifices. I would gladly learn of those who give
so much to Galen, how they dare swear to what
he says. Neither in the liver, spleen, lungs, kid-
neys, nor any other viscus, is such a thing as an
anastomosis to be seen; and by boiling, I have
rendered the whole parenchyma of these organs
so friable that it could be shaken like dust from
the fibres, or picked away with a needle, until
I could trace the fibres of every subdivision,
and see every capillary filament distinctly. I
can therefore boldly affirm, that there is neither
any anastomosis of the vena portae with the
cava, of the arteries with the veins, or of the
capillary ramifications of the biliary ducts,
which can be traced through the entire liver,
with the veins. This alone may be observed in
the recent liver: all the branches of the vena
cava ramifying through the convexity of the
liver, have their tunics pierced with an infinity
of minute holes, as is a sieve, and are fashioned
to receive the blood in its descent. The branches
of the porta are not so constituted, but simply
spread out in subdivisions; and the distribution
of these two vessels is such that, whilst the one
312
WILLIAM HARVEY
runs upon the convexity, the other proceeds
along the concavity of the liver to its outer
margin, and all the while without anastomos-
ing.
In three places only do I find anything that
can be held equivalent to an anastomosis. From
the carotids, as they are creeping over the base
of the brain, numerous interlaced fibres arise,
which afterwards form the choroid plexus, and
passing through the lateral ventricles, finally
unite and terminate in the third sinus, which
performs the office of a vein. In the spermatic
vessels, commonly called vasa praeparantia, cer-
tain minute arteries proceeding from the great
artery adhere to the venae praeparantes, which
they accompany, and are at length taken in and
included within their coats, in such a way that
they seem to have a common ending, so that
where they terminate on the upper portion of
the testis, on that cone-shaped process called
the corpus varicosum et pampiniforme, it is
altogether uncertain whether we are to re-
gard their terminations as veins, or as arteries,
or as both. In the same way are the ultimate
ramifications of the arteries which run to
the umbilical vein, lost in the tunics of this
vessel.
What doubt can there be, if by such channels
the great arteries, distended by the stream of
blood sent into them, are relieved of so great
and obvious a torrent, but that nature would
not have denied distinct and visible passages,
vortices, and estuaries, had she intended to
divert the whole current of the blood, and had
wished in this way to deprive the lesser branches
and the solid parts of all the benefit of the in-
flux of that fluid ?
Finally, I shall quote this single experiment,
which appears to me sufficient to clear up all
doubts about the anastomoses, and their uses,
if any exist, and to set at rest the question of a
passage of the blood from the veins to the ar-
teries, by any special channels, or by regurgita-
tion.
Having laid open the thorax of an animal,
and tied the vena cava near the heart, so that
nothing shall pass from that vessel into its cavi-
ties, and immediately afterwards, having di-
vided the carotid arteries on both sides, the jug-
ular veins being left untouched; if the arteries
be now perceived to become empty but not the
veins, I think it will be manifest that the blood
does nowhere pass from the veins into the ar-
teries except through the ventricles of the
heart. Were it not so, as observed by Galen, we
should see the veins as well as the arteries em-
ptied in a very short time, by the efflux from
their corresponding arteries.
For what further remains, oh Riolanus! I
congratulate both myself and you : myself, for
the opinion with which you have graced my
circulation; and you, for your learned, polished,
and terse production, than which nothing more
elegant can be imagined. For the favour you
have done me in sending me this work, I feel
most grateful, and I would gladly, as in duty
bound, proclaim my sense of its merits, but I
confess myself unequal to the task; for I know
that the Enchiridion bearing the name of Rio-
lanus inscribed upon it, has thereby more of
honour conferred upon it than it can derive
from any praise of mine, which nevertheless I
would yield without reserve. The famous book
will live for ever; and when marble shall have
mouldered, will proclaim to posterity the glory
that belongs to your name. You have most hap-
pily conjoined anatomy with pathology, and
have greatly enriched the subject with a new
and most useful osteology. Proceed in your
worthy career, most illustrious Riolanus, and
love him who wishes that you may enjoy both
happiness and length of days, and that all your
admirable works may conduce to your eternal
fame. WILLIAM HARVEY
A Second Disquisition to John Riolan
IT is now many years, most learned Riolanus,
since, with the aid of the press, I published a
portion of my work. But scarce a day, scarce an
hour, has passed since the birth-day of the
Circulation of the Blood, that I have not
heard something for good or for evil said of this
my discovery. Some abuse it as a feeble infant,
and yet unworthy to have seen the light;
others, again, think the bantling deserves to be
cherished and cared for; these oppose it with
much ado, those patronize it with abundant
commendation; one party holds that I have
completely demonstrated the circulation of the
blood by experiment, observation, and ocular
inspection, against all force and array of argu-
ment; another thinks it scarcely yet sufficient-
ly illustrated — not yet cleared of all objections.
There are some, too, who say that I have shown
a vainglorious love of vivisections, and who
scoff at and deride the introduction of frogs
and serpents, flies, and others of the lower ani-
mals upon the scene, as a piece of puerile levity,
not even refraining from opprobrious epithets.
To return evil speaking with evil speaking,
however, I hold to be unworthy in a philos-
opher and searcher after truth; I believe that I
shall do better and more advisedly if I meet so
many indications of ill breeding with the light
of faithful and conclusive observation. It can-
not be helped that dogs bark and vomit their
foul stomachs, or that cynics should be num-
bered among philosophers; but care can be tak-
en that they do not bite or inoculate their mad
humours, or with their dogs' teeth gnaw the
bones and foundations of truth.
Detractors, mummers, and writers defiled
with abuse, as I resolved with myself never to
read them, satisfied that nothing solid or excel-
lent, nothing but foul terms, was to be expected
from them, so have I held them still less worthy
of an answer. Let them consume on their own
ill nature; they will scarcely find many well-
disposed readers, I imagine, nor does God give
that which is most excellent and chiefly to be
desired — wisdom, to the wicked ; let them go on
railing, I say, until they are weary, if not
ashamed.
If for the sake of studying the meaner ani-
mals you should even enter the bakehouse with
Heraclitus, as related in Aristotle, I bid you
approach; for neither are the immortal gods ab-
sent here, and the great and Almighty Father
is sometimes most visible in His lesser, and to
the eye least considerable works.
In my book On the Motion of the Heart
and Blood in Animals, I have only adduced
those facts from among many other observa-
tions, by which either errors were best refuted,
or truth was most strongly supported; I have
left many proofs, won by dissection and ap-
preciable to sense, as redundant and unneces-
sary; some of these, however, I now supply in
brief terms, for the sake of the studious, and
those who have expressed their desire to have
them.
The authority of Galen is of such weight
with all, that I have seen several hesitate great-
ly with that experiment before them, in which
the artery is tied upon a tube placed within its
cavity; and by which it is proposed to prove
that the arterial pulse is produced by a power
communicated from the heart through the
coats of the arteries, and not from the shock of
the blood contained within them; and thence,
that the arteries dilate as bellows, are not filled
as sacs. This experiment is spoken of by Vesalius,
the celebrated anatomist; but neither Vesalius
nor Galen says that he had tried the experi-
ment, which, however, I did. Vesalius only pre-
scribes, and Galen advises it, to those anxious
to discover the truth, and for their better as-
surance, not thinking of the difficulties that at-
tend its performance, nor of its futility when
done; for indeed, although executed with the
greatest skill, it supplies nothing in support of
the opinion which maintains that the coats of the
vessel are the cause of the pulse; it much rather
proclaims that this is owing to the impulse of
the blood. For the moment you have thrown
your ligature around the artery upon the reed
or tube, immediately, by the force of the blood
thrown in from above, it is dilated beyond the
circle of the tube, by which the flow is im-
peded, and the shock is broken; so that the ar-
WILLIAM HARVEY
tery which is tied only pulsates obscurely, being
now cut off from the full force of the blood that
flows through it, the shock being reverberated,
as it were, from that part of the vessel which is
above the ligature; but if the artery below the
ligature be now divided, the contrary of what
has been maintained will be apparent, from
the spurting of the blood impelled through the
tube; just as happens in the cases of aneurism,
referred to in my book On the Motion of the
Blood, which arise from an erosion of the coats
of the vessel, and when the blood is contained
in a membranous sac, formed not by the coats
of the vessel dilated, but preternaturally pro-
duced from the surrounding tissues and flesh.
The arteries beyond an aneurism of this kind
will be felt beating very feebly, whilst in those
above it and in the swelling itself the pulse will be
perceived of great strength and fulness. And
here we cannot imagine that the pul^tion and
dilatation take place by the coats of the arter-
ies, or any power communicated to the walls of
the sac; they are plainly due to the shock of the
blood.
But that the error of Vesalius, and the inex-
perience of those who assert their belief that
the part below the tube does not pulsate when
the ligature is tied, may be made the more ap-
parent, I can state, after having made the trial,
that the inferior part will continue to pulsate if
the experiment be properly performed; and
whilst they say that when you have undone the
ligature the inferior arteries begin again to pul-
sate, I maintain that the part below beats less
forcibly when the ligature is untied than it did
when the thread was still tight. But the ef-
fusion of blood from the wound confuses every-
thing, and renders the whole experiment unsat-
isfactory and nugatory, so that nothing certain
can be shown, by reason, as I have said, of the
hemorrhage. But if, as I know by experience,
you lay bare an artery, and control the divided
portion by the pressure of your fingers, you
may try many things at pleasure by which the
truth will be made to appear. In the first place,
you will feel the blood coming down in the ar-
tery at each pulsation, and visibly dilating the
vessel. You may also at will suffer the blood to
escape, by relaxing the pressure, and leaving a
small outlet; and you will see that it jets out
with each stroke, with each contraction of the
heart, and with each dilatation of the artery,
as I have said in speaking of arteriotomy, and
the experiment of perforating the heart. And
if you suffer the efflux to go on uninterrupted-
ly, either from the simple divided artery or
from a tube inserted into it, you will be able to
perceive by the sight, and if you apply your
hand, by the touch likewise, every character of
the stroke of the heart in the jet; the rhythm,
order, intermission, force, &c., of its pulsations,
all becoming sensible there, no otherwise than
would the jets from a syringe, pushed in succes-
sion and with different degrees of force, re-
ceived upon the palm of the hand, be obvious
to sight and touch. I have occasionally observed
the jet from a divided carotid artery to be so
forcible, that, when received on the hand, the
blood rebounded to the distance of four or five
feet.
But that the question under discussion, viz.,
that the pulsific power does not proceed from
the heart by the coats of the vessels, may be
set in yet a clearer light, I beg here to refer to
a portion of the descending aorta, about a span
in length, with its division into the two crural
trunks, which I removed from the body of a
nobleman, and which is converted into a bony
tube; by this hollow tube, nevertheless, did the
arterial blood reach the lower extremities of
this nobleman during his life, and cause the ar-
teries in these to beat; and yet the main trunk
was precisely in the same condition as is the ar-
tery in the experiment of Galen, when it is tied
upon a hollow tube; where it was converted
into bone it could neither dilate nor contract
like bellows, nor transmit the pulsific power
from the heart to the inferior vessels; it could
not convey a force which it was incapable of re-
ceiving through the solid matter of the bone.
In spite of all, however, I well remember to
have frequently noted the pulse in the legs and
feet of this patient whilst he lived, for I was
myself his most attentive physician, and he my
very particular friend. The arteries in the in-
ferior extremities of this nobleman must there-
for and of necessity have been dilated by the
impulse of the blood like flaccid sacs, and not
have expanded in the manner of bellows through
the action of their tunics. It is obvious that,
whether an artery be tied over a hollow tube, or
its tunics be converted into a bony and un-
yielding canal, the interruption to the pulsific
power in the inferior part of the vessel must be
the same.
I have known another instance in which a
portion of the aorta near the heart was found
converted into bone, in the body of a nobleman,
a man of great muscular strength. The experi-
ment of Galen, therefore, or, at all events, a
state analogous to it, not effected on purpose
but encountered by accident, makes it suffi-
CIRCULATION OF THE BLOOD
3*5
ciently to appear that compression or ligature of
the coats of an artery does not interfere with the
pulsative properties of its derivative branches;
and indeed, if the experiment which Galen rec-
ommends were properly performed by anyone,
its results would be found in opposition to the
views which Vesalius believed they would sup-
port.
But we do not therefore deny everything
like motion to the tunics of the arteries; on the
contary, we allow them the same motions
which we concede to the heart, viz., a diastole,
and a systole or return from the distended to
the natural state; this much we believe to be ef-
fected by a power inherent in the coats them-
selves. But it is to be observed that they are not
both dilated and contracted by the same, but
by different causes and means; as may be ob-
served of the motions of all parts, and of the
ventricle of the heart itself, which is distended
by the auricle, contracted by its own inherent
power; so, the arteries are dilated by the stroke
of the heart, but they contract or collapse of
themselves.1
You may also perform another experiment
at the same time: if you fill one of two basins of
the same size with blood issuing per saltum from
an artery, the other with venous blood from a
vein of the same animal, you will have an op-
portunity of perceiving by the eye, both im-
mediately and by and by, when the blood in
either vessel has become cold, what differences
there are between them. You will find that it is
not as they believe who fancy that there is one
kind of blood in the arteries and another in the
veins, that in the arteries being of a more florid
colour, more frothy, and imbued with an abun-
dance of I know not what spirits, effervescing
and swelling, and occupying a greater space,
like milk or honey set upon the fire. For were
the blood which is thrown from the left ven-
tricle of the heart into the arteries, fermented
into any such frothy and flatulent fluid, so that
a drop or two distended the whole cavity of
the aorta; unquestionably, upon the subsidence
of this fermentation, the blood would return to
its original quantity of a few drops (and this,
indeed, is the reason that some assign for the
usually empty state of the arteries in the dead
body); and so should it be with the arterial
blood in the cup, for so it is with boiling milk
and honey when they come to cool. But if in
either basin you find blood nearly of the same
colour, not of very different consistency in the
1 See Chapter 3, of the Disquisition on the Motion of
the Heart and Blood.
coagulated state, forcing out serum in the same
manner, and filling the cups to the same height
when cold that it did when hot, this will be
enough for any one to rest his faith upon, and
afford argument enough, I think, for rejecting
the dreams that have been promulgated on the
subject. Sense and reason alike assure us that the
blood contained in the left ventricle is not of a
different nature from that in the right. And
then, when we see that the mouth of the pul-
monary artery is of the same size as the aorta,
and in other respects equal to that vessel, it
were imperative on us to affirm that the pul-
monary artery was distended by a single drop
of spumous blood, as well as the aorta, and so
that the right as well as the left side of the
heart was filled with a brisk or fermenting
blood.
The particulars which especially dispose men's
minds to admit diversity in the arterial and ve-
nous blood are three in number: one, because in
arteriotomy the blood that flows is of a more
florid hue than that which escapes from a vein;
a second, because in the dissection of dead
bodies the left ventricle of the heart, and the
arteries in general, are mostly found empty;
a third, because the arterial blood is believed
to be more spirituous, and being replete with
spirit is made to occupy a much larger space.
The causes and reasons, however, wherefore all
these things are so, present themselves to us
when we ask after them.
ist. With reference to the colour it is to be
observed that wherever the blood issues by a
very small orifice, it is in some measure strained,
and the thinner and lighter part, which usually
swims on the top and is the most penetrating, is
emitted. Thus, in phlebotomy, when the blood
escapes forcibly and to a distance, in a full
stream, and from a large orifice, it is thicker,
has more body, and a darker colour; but, if it
flows from a small orifice, and only drop by
drop, as it usually does when the bleeding fillet
is untied, it is of a brighter hue; for then it is
strained as it were, and the thinner and more
penetrating portion only escapes; in the same
way, in the bleeding from the nose, in that
which takes place from a leech-bite, or from
scarifications, or in any other way by diapedesis
or transudation, the blood is always seen to
have a brighter cast, because the thickness and
firmness of the coats of the arteries render the
outlet or outlets smaller, and less disposed to
yield a ready passage to the outpouring blood;
it happens also that when fat persons are let
blood, the orifice of the vein is apt to be com-
3i6
WILLIAM HARVEY
pressed by the subcutaneous fat, by which the
blood is made to appear thinner, more florid,
and in some sort arterious. On the other hand,
the blood that flows into a basin from a large ar-
tery freely divided, will look venous. The blood
in the lungs is of a much more florid colour than
it is in the arteries, and we know how it is
strained through the pulmonary tissue.
2d. The emptiness of the arteries in the dead
body, which probably mislead Erasistratus in
supposing that they only contained aereal spir-
its, is caused by this, that when respiration
ceases the lungs collapse, and then the passages
through them are closed; the heart, however,
continues for a time to contract upon the blood,
whence we find the left auricle more contracted,
and the corresponding ventricle, as well as the
arteries at large, appearing empty, simply be-
cause there is no supply of blood flowing round
to fill them. In cases, however, in which the
heart has ceased to pulsate and the lungs to
afford a passage to the blood simultaneously, as
in those have died from drowning or syncope,
or who die suddenly, you will find the arteries,
as well as the veins, full of blood.
3d. With reference to the third point, or that
of the spirits, it may be said that, as it is still a
question what they are, how extant in the
body, of what consistency, whether separate
and distinct from the blood and solids, or min-
gled with these — upon each and all of these
points there are so many and such conflicting
opinions, that it is not wonderful that the spir-
its, whose nature is thus left so wholly ambigu-
ous, should serve as the common subterfuge of
ignorance. Persons of limited information,
when they are at a loss to assign a cause for any-
thing, very commonly reply that it is done by
the spirits; and so they bring the spirits into
play upon all occasions; even as indifferent
poets are always thrusting the gods upon the
stage as a means of unravelling the plot, and
bringing about the catastrophe.
Fernelius, and many others, suppose that
there are aereal spirits and invisible substances.
Fernelius proves that there are animal spirits,
by saying that the cells in the brain are appar-
ently unoccupied, and as nature abhors a vacu-
um, he concludes that in the living body they
are filled with spirits, just as Erasistratus had
held that, because the arteries were empty of
blood, therefore they must be filled with spirits.
But medical schools admit three kinds of spir-
its: the natural spirits flowing through the
veins, the vital spirits through the arteries, and
the animal spirits through the nerves; whence
physicians say, out of Galen, that sometimes
the parts of the brain are oppressed by sympa-
thy, because the faculty with the essence, *'. c.,
the spirit, is overwhelmed; and sometimes this
happens independently of the essence. Further,
besides the three orders of influxive spirits ad-
verted to, a like number of implanted or sta-
tionary spirits seem to be acknowledged; but
we have found none of all these spirits by dis-
section, neither in the veins, nerves, arteries,
nor other parts of living animals. Some speak
of corporeal, others of incorporeal spirits; and
they who advocate the corporeal spirits will
have the blood, or the thinner portion of the
blood, to be the bond of union with the soul,
the spirit being contained in the blood as the
flame is in the smoke of a lamp or candle, and
held admixed by the incessant motion of the
fluid; others, again, distinguish between the
spirits and the blood. They who advocate in-
corporeal spirits have no ground of experience
to stand upon; their spirits indeed are synony-
mous with powers or faculties, such as a con-
coctive spirit, a chylopoietic spirit, a procre-
ative spirit, &c. — they admit as many spir-
its, in short, as there are faculties or organs.
But then the schoolmen speak of a spirit of
fortitude, prudence, patience, and the other
virtues, and also of a most holy spirit of wisdom,
and of every divine gift; and they besides sup-
pose that there are good and evil spirits that
roam about or possess the body, that assist or
cast obstacles in the way. They hold some dis-
eases to be owing to a Cacodaemon or evil spirit,
as there are others that are due to a cacochemy
or defective assimilation.
Although there is nothing more uncertain
and questionable, then, than the doctrine of
spirits that is proposed to us, nevertheless phy-
sicians seem for the major part to conclude,
with Hippocrates, that our body is composed
or made up of three elements, viz., containing
parts, contained parts, and causes of action,
spirits being understood by the latter term. But
if spirits are to be taken as synonymous with
causes of activity, whatever has power in the
living body and a faculty of action must be in-
cluded under the denomination. It would ap-
pear, therefore, that all spirits were neither
aereal substances, nor powers, nor habits; and
that all were not incorporeal.
But keeping in view the points that espe-
cially interest us, others, as leading to tedious-
ness, being left unnoticed, it seems that the
spirits which flow by the veins or the arteries
are not distinct from the blood, any more than
CIRCULATION OF THE BLOOD
the flame of a lamp is distinct from the inflam-
mable vapour that is on fire; in short, that the
blood and these spirits signify one and the same
thing, though different— like generous wine
and its spirit; for as wine, when it has lost all its
spirit, is no longer wine, but a vapid liquor or
vinegar; so blood without spirit is not blood,
but something else — clot or cruor; even as a
hand of stone, or of a dead body, is no hand in
the most complete sense, neither is blood void
of the vital principle proper blood; it is imme-
diately to be held as corrupt when deprived of
its spirit. The spirit, therefore, which inheres in
the arteries, and especially in the blood which
fills them, is to be regarded either as its act or
agent, in the same way as the spirit of wine in
wine, and the spirit of aqua vitae in brandy, or
as a flame kindled in alcohol, which lives and
feeds on, or is nourished by itself. The blood,
consequently, though richly imbued with spir-
its, does not swell, nor ferment, nor rise to a
head through them, so as to require and occupy
a larger space — a fact that may be ascertained
beyond the possibility of question by the two
cups of equal size; it is to be regarded as wine,
possessed of a large amount of spirits, or, in the
Hippocratic sense, of signal powers of acting
and effecting.
It is, therefore, the same blood in the arteries
that is found in the veins, although it may be
admitted to be more spirituous, possessed of
higher vital force in the former than in the
latter; but it is not changed into anything more
vaporous, or more aereal, as if there were no
spirits but such as are aereal, and no cause of
action or activity that is not of the nature of
flatus or wind. But neither the animal, natural,
nor vital spirits which inhere in the solids, such
as the ligaments and nerves (especially if they
be of so many different species), and are con-
tained within the viewless interstices of the tis-
sues, are to be regarded as so many different
aereal forms, or kinds of vapour.
And here I would gladly be informed by
those who admit corporeal spirits, but of a gas-
eous or vaporous consistency, in the bodies of
animals, whether or not they have the power of
passing hither and thither, like distinct bodies
independently of the blood ? Or whether the
spirits follow the blood in its motions, either as
integral parts of the fluid or as indissolubly con-
nected with it, so that they can neither quit
the tissues nor pass hither nor thither without
the influx and reflux, and motion of the blood ?
For if the spirits exhaling from the blood, like
the vapour of water attenuated by heat, exist
in a state of constant flow and succession as the
pabulum of the tissues, it necessarily follows
that they are not distinct from this pabulum,
but are incessantly disappearing; whereby it
seems that they can neither have influx nor re-
flux, nor passage, nor yet remain at rest without
the influx, the reflux, the passage of the blood,
which is the fluid that serves as their vehicle or
pabulum.
And next I desire to know of those who tell
us that the spirits are formed in the heart, being
compounded of the vapours or exhalations of
the blood (excited either by the heat of the
heart or the concussion) and the inspired air,
whether such spirits are not to be accounted
much colder than the blood, seeing that both
the elements of their composition, namely, air
and vapour, are much colder? For the vapour
of boiling water is much more bearable than
the water itself; the flame of a candle is less
burning than the red-hot snuff, and burning
charcoal than incandescent iron or brass. Whence
it would appear that spirits of this nature rather
receive their heat from the blood, than that the
blood is warmed by these spirits; such spirits
are rather to be regarded as fumes and excre-
mentitious effluvia proceeding from the body
in the manner of odours, than in any way as
natural artificers of the tissues; a conclusion
which we are the more disposed to admit, when
we see that they so speedily lose any virtue they
may possess, and which they had derived from
the blood as their source — they are at best of a
very frail and evanescent nature. Whence also
it becomes probable that the expiration of the
lungs is a means by which these vapours being
cast off, the blood is fanned and purified; whilst
inspiration is a means by which the blood in its
passage between the two ventricles of the heart
is tempered by the cold of the ambient atmos-
phere, lest, getting heated, and blown up with
a kind of fermentation, like milk or honey set
over the fire, it should so distend the lungs that
the animal got suffocated; somewhat in the
same way, perchance, as one labouring under a
severe asthma, which Galen himself seems to
refer to its proper cause when he says it is owing
to an obstruction of the smaller arteries, viz.,
the vasa venosa et arteriosa. And I have found
by experience that patients affected with asthma
might be brought out of states of very immi-
nent danger by having cupping-glasses applied,
and a plentiful and sudden affusion of cold
water. Thus much— and perhaps it is more than
was necessary— have I said on the subject of
spirits in this place, for I felt it proper to define
3i8
WILLIAM HARVEY
them, and to say something of their nature in a
physiological disquisition.
I shall only further add that they who des-
cant on the calidum innatum or innate heat, as
an instrument of nature available for every
purpose, and who speak of the necessity of heat
as the cherisher and retainer in life of the sev-
eral parts of the body, who at the same time ad-
mit that this heat cannot exist unless connected
with something, and because they find no sub-
stance of anything like commensurate mobility,
or which might keep pace with the rapid influx
and reflux of this heat (in affections of the mind
especially), take refuge in spirits as most subtile
substances, possessed of the most penetrating
qualities, and highest mobility— these persons
see nothing less than the wonderful and almost
divine character of the natural operations as
proceeding from the instrumentality of this
common agent, viz., the calidum innatum; they
further regard these spirits as of a sublime, lucid,
ethereal, celestial, or divine nature, and the
bond of the soul; even as the vulgar and unlet-
tered, when they do not comprehend the causes
of various effects, refer them to the immediate
interposition of the Deity. Whence they de-
clare that the heat perpetually flowing into the
several parts is in virtue of the influx of spirits
through the channels of the arteries; as if the
blood could neither move so swiftly, nor pen-
etrate so intimately, nor cherish so effectually.
And such faith do they put in this opinion,
such lengths are they carried by their belief,
that they deny the contents of the arteries to
be blood! And then they proceed with trivial
reasonings to maintain that the arterial blood
is of a peculiar kind, or that the arteries are
filled with such aereal spirits, and not with
blood; all the while, in opposition to every-
thing which Galen has advanced against Erasis-
tratus, both on grounds of experiment and of
reason. But that arterial blood differs in noth-
ing essential from venous blood has been al-
ready sufficiently demonstrated; and our senses
likewise assure us that the blood and spirits do
not flow in the arteries separately and disjoined,
but as one body.
We have occasion to observe so often as our
hands, feet, or ears have become stiff and cold,
that as they recover again by the warmth that
flows into them, they acquire their natural
colour and heat simultaneously; that the veins
which had become small and shrunk, swell
visibly and enlarge, so that when they regain
their heat suddenly they become painful; from
which it appears that that which by its influx
brings heat is the same which causes repletion
and colour; now this can be and is nothing but
blood.
When an artery and a vein are divided, any-
one may clearly see that the part of the vein
towards the heart pours out no blood, whilst
that beyond the wound gives a torrent; the di-
vided artery, on the contrary (as in my experi-
ment on the carotids), pours out a flood of pure
blood from the orifice next the heart, and in
jets as if it were forced from a syringe, whilst
from the farther orifice of the divided artery
little or no blood escapes. This experiment
therefore plainly proves in what direction the
current sets in either order of vessels— towards
the heart in the veins, from the heart in the
arteries; it also shows with what velocity the
current moves, not gradually and by drops, but
even with violence. And lest anyone, by way of
subterfuge, should take shelter in the notion of
invisible spirits, let the orifice of the divided
vessel be plunged under water or oil, when, if
there be any air contained m it, the fact will be
proclaimed by a succession of visible bubbles.
Hornets, wasps, and other insects of the same
description plunged in oil, and so suffocated,
emit bubbles of air from their tail whilst they
are dying; whence it is not improbable that
they thus respire when alive; for all animals
submerged and drowned, when they finally sink
to the bottom and die, emit bubbles of air from
the mouth and lungs. It is also demonstrated by
the same experiment, that the valves of the
veins act with such accuracy, that air blown in-
to them does not penetrate; much less then can
blood make its way through them: it is certain,
I say, that neither sensibly nor insensibly, nor
gradually and drop by drop, can any blood pass
from the heart by the veins.
And that no one may seek shelter in asserting
that these things are so when nature is disturbed
and opposed, but not when she is left to herself
and at liberty to act; that the same things do
not come to pass in morbid and unusual states
as in the healthy and natural condition; they
are to be met by saying that, if it were so, if it
happened that so much blood was lost from the
farther orifice of a divided vein because nature
was disturbed, still that the incision does not
close the nearer orifice, from which nothing
either escapes or can be expressed, whether na-
ture be disturbed or not. Others argue in the
same way, maintaining that, although the blood
immediately spurts out in such profusion with
every beat, when an artery is divided near the
heart, it does not therefore follow that the
CIRCULATION OF THE BLOOD
3*9
blood is propelled by the pulse when the heart
and artery are entire. It is most probable, how-
ever, that every stroke impels something; and
that there would be no pulse of the container,
without an impulse being communicated to the
thing contained, seems certain. Yet some, that
they may seize upon a further means of defence,
and escape the necessity of admitting the circu-
lation, do not fear to affirm that the arteries in
the living body and in the natural state are
already so full of blood that they are incapable
of receiving another drop; and so also of the
ventricles of the heart. But it is indubitable
that, whatever the degree of distension and the
extent of contraction of the heart and arteries,
they are still in a condition to receive an addi-
tional quantity of blood forced into them, and
that this is far more than is usually reckoned in
grains or drops, seems also certain. For if the
ventricles become so excessively distended that
they will admit no more blood, the heart ceases
to beat (and we have occasional opportunities
of observing the fact in our vivisections) and,
continuing tense and resisting, death by as-
phyxia ensues.
In the work, On the Motion of the Heart and
Blood, I have already sufficiently discussed the
question as to whether the blood in its motion
was attracted, or impelled, or moved by its own
inherent nature. I have there also spoken at
length of the action and office, of the dilatation
and contraction of the heart, and have shown
what these truly are, and how the heart con-
tracts during the diastole of the arteries; so that
I must hold those who take points for dispute
from among them as either not understanding
the subject, or as unwilling to look at things for
themselves, and to investigate them with their
own senses.1
For my part, I believe that no other kind of
attraction can be demonstrated in the living
body save that of the nutriment, which gradu-
ally and incessantly passes on to supply the
waste that takes place in the tissues; in the
same way as the oil rises in the wick of a lamp to
be consumed by the flame. Whence I conclude
that the primary and common organ of all sen-
sible attraction and impulsion is of the nature
of sinew (nervus), or fibre, or muscle, and this to
the end that it may be contractile, that con-
tracting it may be shortened, and so either
stretch out, draw towards, or propel. But these
topics will be better discussed elsewhere, when
we speak of the organs of motion in the animal
body.
1 See chapter 14.
To those who repudiate the circulation be-
cause they neither see the efficient nor final
cause of it, and who exclaim, cut bono? I have
yet to reply, having hitherto taken no note of
the ground of objection which they take up.
And first I own I am of opinion that our first
duty is to inquire whether the thing be or not,
before asking wherefore it is ? for from the facts
and circumstances which meet us in the circula-
tion admitted, established, the ends and objects
of its institution are especially to be sought.
Meantime I would only ask, how many things
we admit in physiology, pathology, and thera-
peutics, the causes of which are unknown to us ?
That there are many, no one doubts — the causes
of putrid fevers, of revulsions, of the purgation
of excrementitious matters, among the number.
Whoever, therefore, sets himself in opposi-
tion to the circulation, because, if it be ac-
knowledged, he cannot account fora variety of
medical problems, nor in the treatment of dis-
eases and the administration of medicines, give
satisfactory reasons for the phenomena that ap-
pear; or who will not see that the precepts he
has received from his teachers are false; or who
thinks it unseemly to give up accredited opin-
ions; or who regards it as in some sort criminal
to call in question doctrines that have descended
through a long succession of ages, and carry the
authority of the ancients — toall of these I reply:
that the facts cognizable by the senses wait upon
no opinions, and that the works of nature bow to
no antiquity; for indeed there is nothing either
more ancient or of higher authority than nature.
To those who object to the circulation as
throwing obstacles in the way of their explana-
tions of the phenomena that occur in medical
cases (and there are persons who will not be
content to take up with a new system, unless it
explains everything, as in astronomy), and who
oppose it with their own erroneous assump-
tions, such as that, if it be true, phlebotomy
cannot cause revulsion, seeing that the blood
will still continue to be forced into the affected
part; that the passage of excrementitious mat-
ters and foul humours through the heart, that
most noble and principal viscus, is to be appre-
hended; that an efflux and excretion, occasion-
ally of foul and corrupt blood, takes place from
the same body, from different parts, even from
the same part and at the same time, which,
were the blood agitated by a continuous cur-
rent, would be shaken and effectually mixed in
passing through the heart, and many points of
the like kind admitted in our medical schools,
which are seen to be repugnant to the doctrine
320
WILLIAM HARVEY
of the circulation — to them I shall not answer
further here, than that the circulation is not
always the same in every place, and at every
time, but is contingent upon many circum-
stances: the more rapid or slower motion of the
blood, the strength or weakness of the heart as
the propelling organ, the quantity and quality
or constitution of the blood, the rigidity or
laxity of the tissues, and the like. A thicker
blood, of course, moves more slowly through
narrower channels; it is more effectually strained
in its passage through the substance of the liver
than through that of the lungs. It has not the
same velocity through flesh and the softer par-
enchyma tous structures and through sinewy
parts of greater compactness and consistency:
for the thinner and purer and more spirituous
part permeates more quickly, the thicker more
earthy and indifferently concocted portion
moves more slowly, or is refused admission. The
nutritive portion, or ultimate aliment of the
tissues, the dew or cambium, is of a more pene-
trating nature, inasmuch as it has to be added
everywhere, and to everything that grows and
is nourished in its length and thickness, even to
the horns, nails, hair and feathers; and then the
excrementitious matters have to be secreted in
some places, where they accumulate, and either
prove a burthen or are concocted. But I do not
imagine that the excrementitious fluids or bad
humours when once separated, nor the milk,
the phlegm, and the spermatic fluid, nor the
ultimate nutritive part, the dew or cambium,
necessarily circulate with the blood: that which
nourishes every part adheres and becomes ag-
glutinated to it. Upon each of these topics and
various others besides, to be discussed and dem-
onstrated in their several places, viz., in the
physiology and other parts of the art of medi-
cine, as well as of the consequences, advantages
or disadvantages of the circulation of the blood,
I do not mean to touch here; it were fruitless
indeed to do so until the circulation has been es-
tablished and conceded as a fact. And here the
example of astronomy is by no means to be fol-
lowed, in which from mere appearances or
phenomena that which is in fact, and the reason
wherefore it is so, are investigated. But as he
who inquires into the cause of an eclipse must
be placed beyond the moon if he would ascer-
tain it by sense, and not by reason, still, in ref-
erence to things sensible, things that come un-
der the cognizance of the senses, no more cer-
tain demonstration or means of gaining faith
can be adduced than examination by the senses,
than ocular inspection.
There is one remarkable experiment which I
would have every one try who is anxious for
truth, and by which it is clearly shown that the
arterial pulse is owing to the impulse of the
blood. Let a portion of the dried intestine of a
dog or wolf, or any other animal, such as we see
hung up in the druggists' shops, be taken and
filled with water, and then secured at both ends
like a sausage : by tapping with the finger at one
extremity, you will immediately feel a pulse
and vibration in any other part to which you
apply the fingers, as you do when you feel the
pulse at the wrist. In this way, indeed, and also
by means of a distended vein, you may accurate-
ly either m the dead or living body, imitate
and show every variety of the pulse, whether as
to force, frequency, volume, rhythm, &c. Just
as in a long bladder full of fluid, or in an oblong
drum, every stroke upon one end is imme-
diately felt at the other; so also in a dropsy of the
belly and in abscesses under the skin, we are ac-
customed to distinguish between collections of
fluid and of air, between anasarca and tympan-
ites in particular. If a slap or push given on one
side is clearly felt by a hand placed on the other
side, we judge the case to be tympanites, not, as
falsely asserted, because we hear a sound like
that of a drum, and this produced by flatus,
which never happens; but because, as in a
drum, even the slightest tap passes through and
produces a certain vibration on the opposite
side; for it indicates that there is a serous and
ichorous substance present, of such a consist-
ency as urine, and not any sluggish or viscid
matter as in anasarca, which when struck re-
tains the impress of the blow or pressure, and
does not transmit the impulse.
Having brought forward this experiment I
may observe that a most formidable objection
to the circulation of the blood rises out of it,
which, however, has neither been observed nor
adduced by anyone who has written against
me. When we see by the experiment just de-
scribed, that the systole and diastole of the
pulse can be accurately imitated without any
escape of fluid, it is obvious that the same thing
may take place in the arteries from the stroke
of the heart, without the necessity for a circu-
lation, but like Euripus, with a mere motion of
the blood alternately backwards and forwards.
But we have already satisfactorily replied to
this difficulty; and now we venture to say that
the thing could not be so in the arteries of a liv-
ing animal; to be assured of this it is enough to
see that the right auricle is incessantly injecting
the right ventricle of the heart with blood, the
CIRCULATION OF THE BLOOD
321
return of which is effectually prevented by the
tricuspid valves; the left auricle in like manner
filling the left ventricle, the return of the blood
there being opposed by the mitral valves; and
then the ventricles in their turn are propelling
the blood into either great artery, the reflux in
each being prevented by the sigmoid valves in
its orifice. Either, consequently, the blood must
move on incessantly through the lungs, and in
like manner within the arteries of the body, or
stagnating and pent up, it must rupture the
containing vessels, or choke the heart by over
distension, as I have shown it to do in the vivi-
section of a snake, described in my book On the
Motion of the Blood. To resolve this doubt I
shall relate two experiments among many
others, the first of which, indeed, I have al-
ready adduced, and which show with singular
clearness that the blood flows incessantly and
with great force and in ample abundance in the
veins towards the heart. The internal jugular
vein of a live fallow deer having been exposed
(many of the nobility and his Most Serene
Majesty the King, my master, being present),
was divided; but a few drops of blood were ob-
served to escape from the lower orifice rising up
from under the clavicle; whilst from the supe-
rior orifice of the vein and coming down from
the head, a round torrent of blood gushed forth.
You may observe the same fact any day in
practising phlebotomy: if with a finger you
compress the vein a little below the orifice, the
flow of blood is immediately arrested; but the
pressure being removed, forthwith the flow re-
turns as before.
From any long vein of the forearm get rid of
the blood as much as possible by holding the
hand aloft and pressing the blood towards the
trunk, you will perceive the vein collapsed and
leaving, as it were, in a furrow of the skin; but
now compress the vein with the point of a fin-
ger, and you will immediately perceive all that
part of it which is towards the hand, to enlarge
and to become distended with the blood that is
coming from the hand. How comes it when the
breath is held and the lungs thereby com-
pressed, a large quantity of air having been
taken in, that the vessels of the chest are at the
same time obstructed, the blood driven into
the face, and the eyes rendered red and suf-
fused ? Why is it, as Aristotle asks in his Prob-
lems^ that all the actions are more energetically
performed when the breath is held than when
it is given? In like manner, when the frontal
and lingual veins are incised, the blood is made
to flow more freely by compressing the neck
and holding the breath. I have several times
opened the breast and pericardium of a man
within two hours after his execution by hang-
ing, and before the colour had totally left the
face, and in presence of many witnesses, have
demonstrated the right auricle of the heart and
the lungs distended with blood; the auricle in
particular of the size of a large man's fist, and so
full of blood that it looked as if it would burst.
This great distension, however, had disap-
peared next day, the body having stiffened and
become cold, and the blood having made its
escape through various channels. These and
other similar facts, therefore, make it suf-
ficiently certain that the blood flows through
the whole of the veins of the body towards the
base of the heart, and that unless there was a
further passage afforded it, it would be pent up
in these channels, or would oppress and over-
whelm the heart; as on the other hand, did it
not flow outwards by the arteries, but was
found regurgitating, it would soon be seen how
much it would oppress.
I add another observation. A noble knight,
Sir Robert Darcy, an ancestor of that cele-
brated physician and most learned man, my
very dear friend Dr. Argent, when he had
reached to about the middle period of life,
made frequent complaint of a certain distressing
pain in the chest, especially in the night season ;
so that dreading at one time syncope, at an-
other suffocation in his attacks he led an un-
quiet and anxious life. He tried many reme-
dies in vain, having had the advice of almost
every medical man. The disease going on from
bad to worse, he by and by became cachectic and
dropsical, and finally, grievously distressed, he
died in one of his paroxysms. In the body of
this gentleman, at the inspection of which
there were present Dr. Argent, then president
of the College of Physicians, and Dr. Gorge, a
distinguished theologian and preacher, who was
pastor of the parish, we found the wall of the
left ventricle of the heart ruptured, having a
rent in it of size sufficient to admit any of my
fingers, although the wall itself appeared suf-
ficiently thick and strong; this laceration had
apparently been caused by an impediment to
the passage of the blood from the left ventricle
into the arteries.
I was acquainted with another strong man,
who having received an injury and affront from
one more powerful than himself, and upon
whom he could not have his revenge, was so
overcome with hatred and spite and passion,
which he yet communicated to no one, that at
WILLIAM HARVEY
last he fell into a strange distemper, suffering
from extreme oppression and pain of the heart
and breast, and the prescriptions of none of the
very best physicians proving of any avail, he
fell in the course of a few years into a scorbutic
and cachectic state, became tabid and died.
This patient only received some little relief
when the whole of his chest was pummelled or
kneaded by a strong man, as a baker kneads
dough. His friends thought him poisoned by
some maleficent influence, or possessed with an
evil spirit. His jugular arteries, enlarged to the
size of the thumb, looked like the aorta itself,
or they were as large as the descending aorta;
they had pulsated violently, and appeared like
two long aneurisms. These symptoms had led
to trying the effects of arteriotomy in the tem-
ples, but with no relief. In the dead body I
found the heart and aorta so much gorged and
distended with blood, that the cavities of the
ventricles equalled those of a bullock's heart in
size. Such is the force of the blood pent up, and
such are the effects of its impulse.
We may, therefore, conclude, that although
there may be impulse without any exit, as il-
lustrated in the experiment lately spoken of,
still that this could not take place in the vessels
of living creatures without most serious dangers
and impediments. From this, however, it is
manifest that the blood in its course does not
everywhere pass with the same celerity, nei-
ther with the same force in all places and at all
times, but that it varies greatly according to
age, sex, temperament, habit of body, and
other contingent circumstances, external as
well as internal, natural or non-natural. For it
does not course through intricate and obstruct-
ed passages with the same readiness that it does
through straight, unimpeded, and pervious
channels. Neither does it run through close,
hard, and crowded parts with the same velocity
as through spongy, soft, and permeable tissues.
Neither does it flow and penetrate with such
swiftness when the impulse is slow and weak, as
when this is forcible and frequent, in which
case the blood is driven onwards with vigour
and in large quantity. Nor is the same blood,
when it has become more consistent or earthy,
so penetrative as when it is more serous and at-
tenuated or liquid. And then it seems only rea-
sonable to think that the blood in its circuit
passes more slowly through the kidneys than
through the substance of the heart; more swift-
ly through the liver than through the kidneys;
through the spleen more quickly than through
the lungs, and through the lungs more speedUy
than through any of the other viscera or the
muscles, in proportion always to the denseness
or sponginess of the tissue of each.
We may be permitted to take the same view
of the influence of age, sex, temperament, and
habit of body, whether this be hard or soft; of
that of the ambient cold which condenses bod-
ies, and makes the veins in the extremities to
shrink and almost to disappear, and deprives
the surface both of colour and heat; and also of
that of meat and drink which render the blood
more watery, by supplying fresh nutritive mat-
ter. From the veins, therefore, the blood flows
more freely in phlebotomy when the body is
warm than when it is cold. We also observe the
signal influence of the affections of the mind
when a timid person is bled and happens to
faint: immediately the flow of blood is arrested,
a deadly pallor overspreads the surface, the
limbs stiffen, the ears sing, the eyes are dazzled
or blinded, and, as it were, convulsed. But here
I come upon a field where I might roam freely
and give myself up to speculation. And, in-
deed, such a flood of light and truth breaks in
upon me here; occasion offers of explaining so
many problems, of resolving so many doubts,
of discovering the causes of so many slighter and
more serious diseases, and of suggesting reme-
dies for their cure, that the subject seems al-
most to demand a separate treatise. And it will
be my business in my Medical Observations, to
lay before my reader matter upon all these top-
ics which shall be worthy of the gravest con-
sideration.
And what indeed is more deserving of atten-
tion than the fact that in almost every affec-
tion, appetite, hope, or fear, our body suffers,
the countenance changes, and the blood appears
to course hither and thither. In anger the eyes
are fiery and the pupils contracted; in modesty
the cheeks are suffused with blushes; in fear,
and under a sense of infamy and of shame, the
face is pale, but the ears burn as if for the evil
they heard or were to hear; in lust how quickly
is the member distended with blood and erect-
ed! But, above all, and this is of the highest in-
terest to the medical practitioner, how speedily
is pain relieved or removed by the detraction
of blood, the application of cupping-glasses, or
the compression of the artery which leads to a
part! It sometimes vanishes as if by magic. But
these are topics that I must refer to my Medical
Observations, where they will be found exposed
at length and explained.
Some weak and inexperienced persons vainly
seek by dialectics and far-fetched arguments,
CIRCULATION OF THE BLOOD
323
either to upset or establish things that are only
to be founded on anatomical demonstration,
and believed on the evidence of the senses. He
who truly desires to be informed of the question
in hand, and whether the facts alleged be sensi-
ble, visible, or not, must be held bound either
to look for himself, or to take on trust the con-
clusions to which they have come who have
looked; and indeed there is no higher method of
attaining to assurance and certainty. Who
would pretend to persuade those who had never
tasted wine that it was a drink much pleasanter
to the palate than water? By what reasoning
should we give the blind from birth to know
that the sun was luminous, and far surpassed the
stars in brightness? And so it is with the circu-
lation of the blood, which the world has now
had before it for so many years, illustrated by
proofs cognizable by the senses, and confirmed
by various experiments. No one has yet been
found to dispute the sensible facts, the motion,
efflux and afflux of the blood, by like observa-
tions based on the evidence of sense, or to
oppose the experiments adduced, by other
experiments of the same character; nay, no one
has yet attempted an opposition on the ground
of ocular testimony.
There have not been wanting many who, in-
experienced and ignorant of anatomy, and mak-
ing no appeal to the senses in their opposition,
have, on the contrary, met it with empty as-
sertions, and mere suppositions, with assertions
derived from the lessons of teachers and cap-
tious cavillings; many, too, have vainly sought
refuge in words, and these not always very
nicely chosen, but reproachful and contume-
lious; which, however, have no further effect
than to expose their utterer's vanity and weak-
ness, and ill breeding and lack of the arguments
that are to be sought in the conclusions of the
senses, and false sophistical reasonings that seem
utterly opposed to sense. Even as the waves of
the Sicilian sea, excited by the blast, dash
against the rocks around Charybdis, and then
hiss and foam, and are tossed hither and thither;
so do they who reason against the evidence of
their senses. *
Were nothing to be acknowledged by the
senses without evidence derived from reason, or
occasionally even contrary to the previously re-
ceived conclusions of reason, there would now
be no problem left for discussion. Had we not
our most perfect assurances by the senses, and
were not their perceptions confirmed by rea-
soning, in the same way as geometricians pro-
ceed with their figures, we should admit no
science of any kind; for it is the business of ge-
ometry, from things sensible, to make rational
demonstration of things that are not sensible;
to render credible or certain things abstruse
and beyond sense from things more manifest
and better known. Aristotle counsels us better
when, in treating of the generation of bees, he
says: "Faith is to be given to reason, if the mat-
ters demonstrated agree with those that are
perceived by the senses; when the things have
been thoroughly scrutinized, then are the senses
to be trusted rather than the reason."1 Whence
it is our duty to approve or disapprove, to re-
ceive or reject everything only after the most
careful examination; but to examine, to test
whether anything have been well or ill ad-
vanced, to ascertain whether some falsehood
does not lurk under a proposition, it is impera-
tive on us to bring it to the proof of sense, and
to admit or reject it on the decision of sense.
Whence Plato in his Critias, says that the ex-
planation of those things is not difficult of
which we can have experience; whilst they are
not of apt scientific apprehension who have no
experience.
How difficult is it to teach those who have no
experience, the things of which they have not
any knowledge by their senses! And how use-
less and intractable, and unimpregnable to true
science are such auditors! They show the judg-
ment of the blind in regard to colours, of the
deaf in reference to concords. Who ever pre-
tended to teach the ebb and flow of the tide, or
from a diagram to demonstrate the measure-
ments of the angles and the proportions of the
sides of a triangle to a blind man, or to one who
had never seen the sea nor a diagram ? He who
is not conversant with anatomy, inasmuch as
he forms no conception of the subject from the
evidence of his own eyes, is virtually blind to
all that concerns anatomy, and unfit to appre-
ciate what is founded thereon; he knows noth-
ing of that which occupies the attention of the
anatomist, nor of the principles inherent in
the nature of the things which guide him in his
reasonings; facts and inferences as well as their
sources are alike unknown to such a one. But
no kind of science can possibly flow, save from
some preexisting knowledge of more obvious
things; and this is one main reason why our
science in regard to the nature of celestial bod-
ies, is so uncertain and conjectural. I would ask
of those who profess a knowledge of the causes
of all things, why the two eyes keep constantly
moving together, up or down, to this side or to
1 On the Generation of Animals ^ in. 10.
3*4
WILLIAM HARVEY
that, and not independently, one looking this
way, another that; why the two auricles of the
heart contract simultaneously, and the like?
Are fevers, pestilence, and the wonderful prop-
erties of various medicines to be denied because
their causes are unknown ? Who can tell us why
the foetus in utero, breathing no air up to the
tenth month of its existence, is yet not suffo-
cated? Born in the course of the seventh or
eighth month, and having once breathed, it is
nevertheless speedily suffocated if its respira-
tion be interrupted. Why can the foetus still
contained within the uterus, or enveloped in
the membranes, live without respiration; whilst
once exposed to the air, unless it breathes it in-
evitably dies P1
Observing that many hesitate to acknowl-
edge the circulation, and others oppose it, be-
cause, as I conceive, they have not rightly un-
derstood me, I shall here recapitulate briefly
what I have said in my work On the Motion of
the Heart and Blood. The blood contained in the
veins, in its magazine, and where it is collected
in largest quantity, viz^ in the vena cava, close
to the base of the heart and right auricle, grad-
ually increasing in temperature by its internal
heat, and becoming attenuated, swells and rises
like bodies in a state of fermentation, whereby
the auricle being dilated, and then contracting,
in virtue of its pulsative power, forthwith de-
livers its charge into the right ventricle; which
being filled, and the systole ensuing, the charge,
hindered from returning into the auricle by the
tricuspid valves, is forced into the pulmonary
artery, which stands open to receive it, and is
immediately distended with it. Once in the
pulmonary artery, the blood cannot return, by
reason of the sigmoid valves; and then the
lungs, alternately expanded and contracted
during inspiration and expiration, afford it pas-
sage by the proper vessels into the pulmonary
veins; from the pulmonary veins, the left auri-
cle, acting equally and synchronously with the
right auricle, delivers the blood into the left
ventricle; which acting harmoniously with the
right ventricle, and all regress being prevented
by the mitral valves, the blood is projected into
the aorta, and consequently impelled into all
the arteries of the body. The arteries, filled by
this sudden push, as they cannot discharge
themselves so speedily, are distended; they re-
ceive a shock, or undergo their diastole. But as
this process goes on incessantly, I infer that the
arteries both of the lungs and of the body at
1 Sec Chapter 6, of the Disquisition on the Motion of
the Heart and Blood.
large, under the influence of such a multitude
of strokes of the heart and injections of blood,
would finally become so over-gorged and dis-
tended that either any further injection must
cease, or the vessels would burst, or the whole
blood in the body would accumulate within
them, were there not an exit provided for it.
The same reasoning is applicable to the ven-
tricles of the heart: distended by the ceaseless
action of the auricles, did they not dis bur then
themselves by the channels of the arteries, they
would by and by become over-gorged, and be
fixed and made incapable of all motion. Now
this, my conclusion, is true and necessary, if
my premises be true; but that these are either
true or false, our senses must inform us, not our
reason — ocular inspection, not any process of
the mind.
I maintain, further, that the blood in the
veins always and everywhere flows from less to
greater branches, and from every part towards
the heart; whence I gather that the whole
charge which the arteries receive, and which is
incessantly thrown into them, is delivered to
the veins, and flows back by them to the source
whence it came. In this way, indeed, is the cir-
culation of the blood established: by an efflux
and reflux from and to the heart; the fluid be-
ing forcibly projected into the arterial system,
and then absorbed and imbibed from every
part by the veins, it returns through these in a
continuous stream. That all this is so, sense as-
sures us; and necessary inference from the per-
ceptions of sense takes away all occasion for
doubt. Lastly, this is what I have striven, by
my observations and experiments, to illustrate
and make known ; I have not endeavoured from
causes and probable principles to demonstrate
my propositions, but, as of higher authority, to
establish them by appeals to sense and experi-
ment, after the manner of anatomists.
And here I would refer to the amount of
force, even of violence, which sight and touch
make us aware of in the heart and greater arter-
ies; and to the systole and diastole constituting
the pulse in the large warm-blooded animals,
which I do not say*is equal in all the vessels con-
taining blood, nor in all animals that have
blood; but which is of such a nature and
amount in all, that a flow and rapid passage of
the blood through the smaller arteries, the in-
terstices of the tissues, and the branches of the
veins, must of necessity take place; and, there-
fore, there is a circulation.
For neither do the most minute arteries, nor
the veins, pulsate; but the larger arteries and
CIRCULATION OF THE BLOOD
3*5
those near the heart pulsate, because they do
not transmit the blood so quickly as they re-
ceive it.1 Having exposed an artery, and di-
vided it so that the blood shall flow out as fast
and freely as it is received, you will scarcely
perceive any pulse in that vessel; and for the
simple reason that, an open passage being af-
forded, the blood escapes, merely passing
through the vessel, not distending it. In fishes,
serpents, and the colder animals, the heart
beats so slowly and feebly that a pulse can
scarcely be perceived in the arteries; the blood
in them is transmitted gradually. Whence in
them, as also in the smaller branches of the ar-
teries in man, there is no distinction between
the coats of the arteries and veins, because the
arteries have to sustain no shock from the im-
pulse of the blood.
An artery denuded and divided in the way I
have indicated, sustains no shock, and therefore
does not pulsate; whence it clearly appears that
the arteries have no inherent pulsative power,
and that neither do they derive any from the
heart; but that they undergo their diastole
solely from the impulse of the blood; for in the
full stream, flowing to a distance, you may see
the systole and diastole, all the motions of the
heart — their order, force, rhythm, &c.,2 as it
were in a mirror, and even perceive them by
the touch. Precisely as in the water that is
forced aloft, through a leaden pipe, by work-
ing the piston of a forcing-pump, each stroke of
which, though the jet be many feet distant, is
nevertheless distinctly perceptible — the begin-
ning, increasing strength, and end of the im-
pulse, as well as its amount, and the regularity
or irregularity with which it is given, being in-
dicated, the same precisely is the case from the
orifice of a divided artery; whence, as in the in-
stance of the forcing engine quoted, you will
perceive that the efflux is uninterrupted, al-
though the jet is alternately greater and less.
In the arteries, therefore, besides the concussion
or impulse of the blood, the pulse or beat of the
artery, which is not equally exhibited in all,
there is a perpetual flow and motion of the
blood, which returns in an unbroken stream to
the point from whence it commenced — the
right auricle of the heart.
All these points you may satisfy yourself
upon, by exposing one of the longer arteries,
and having taken it between your finger and
thumb, dividing it on the side remote from the
1 See Chapter 3, of the Disquisition on the Motion of
the Heart and Blood.
heart. By the greater or less pressure of your
fingers, you can have the vessel pulsating less or
more, or losing the pulse entirely, and recover-
ing it at will. And as these things proceed thus
when the chest is uninjured, so also do they go
on for a short time when the thorax is laid open,
and the lungs having collapsed, all the respira-
tory motions have ceased; here, nevertheless,
for a little while you may perceive the left auri-
cle contracting and emptying itself, and becom-
ing whiter; but by and by growing weaker and
weaker, it begins to intermit, as does the left
ventricle also, and then it ceases to beat alto-
gether, and becomes quiescent. Along with
this, and in the same measure, does the stream
of blood from the divided artery grow less and
less, the pulse of the vessel weaker and weaker,
until at last, the supply of blood and the im-
pulse of the left ventricle failing, nothing es-
capes from it. You may perform the same ex-
periment, tying the pulmonary veins, and so
taking away the pulse of the left auricle, or
relaxing the ligature, and restoring it at pleas-
ure. In this experiment, too, you will observe
what happens in moribund animals, war., that
the left ventricle first ceases from pulsation and
motion, then the left auricle, next the right
ventricle, finally the right auricle; so that
where the vital force and pulse first begin, there
do they also last fail.
All of these particulars having been recog-
nized by the senses, it is manifest that the
blood passes through the lungs, not through
the septum, and only through them when they
are moved in the act of respiration, not when
they are collapsed and quiescent; whence we see
the probable reason wherefore nature has in-
stituted the foramen ovale in the foetus, instead
of sending the blood by the way of the pulmo-
nary artery into the left auricle and ventricle,
which foramen she closes when the newborn
creature begins to breathe freely. We can also
now understand why, when the vessels of the
lungs become congested and oppressed, and in
those who are affected with serious diseases, it
should be so dangerous and fatal a symptom
when the respiratory organs become implicated.
We perceive, further, why the blood is so
florid in the lungs, which is, because it is thin-
ner, as having there to undergo filtration.
Still further; from the summary which pre-
cedes, and by way of satisfying those who are
importunate in regard to the causes of the cir-
culation, and incline to regard the power of the
heart as competent to everything—as that it is
not only the seat and source of the pulse which
326
WILLIAM HARVEY
propels the blood, but also, as Aristotle thinks,
of the power which attracts and produces it;
moreover, that the spints are engendered by the
heart, and the influxive vital heat, in virtue of
the innate heat of the heart, as the immediate
instrument of the soul, or common bond and
prime organ in the performance of every act of
vitality; in a word, that the motion, perfec-
tion, heat, and every property besides of the
blood and spirits are derived from the heart, as
their fountain or original (a doctrine as old as
Aristotle, who maintained all these qualities to
inhere in the blood, as heat inheres in boiling
water or pottage), and that the heart is the
primary cause of pulsation and life; to those
persons, did I speak openly, I should say that I
do not agree with the common opinion; there
are numerous particulars to be noted in the pro-
duction of the parts of the body which incline
me this way, but which it does not seem ex-
pedient to enter upon here. Before long, per-
haps, I shall have occasion to lay before the
world things that are more wonderful than
these, and that are calculated to throw still
greater light upon natural philosophy.
Meantime I shall only say, and, without pre-
tending to demonstrate it, propound —with the
good leave of our learned men, and with all re-
spect for antiquity — that the heart, with the
veins and arteries and the blood they contain,
is to be regarded as the beginning and author,
the fountain and original of all things in the
body, the primary cause of life; and this in the
same acceptation as the brain with its nerves,
organs of sense and spinal marrow inclusive, is
spoken of as the one and general organ of sensa-
tion. But if by the word "heart" the mere body
of the heart, made up of its auricles and ven-
tricles, be understood, then I do not believe
that the heart is the fashioner of the blood;
neither do I imagine that the blood has powers,
properties, motion, or heat, as the gift of the
heart; lastly, neither do I admit that the cause
of the systole and contraction is the same as
that of the diastole or dilatation, whether in the
arteries, auricles, or ventricles; for I hold that
that part of the pulse which is designated the
diastole depends on another cause different
from the systole, and that it must always and
everywhere precede any systole; I hold that the
innate heat is the first cause of dilatation, and
that the primary dilatation is in the blood it-
self, after the manner of bodies in a state of fer-
mentation, gradually attenuated and swelling,
and that in the blood is this finally extinguished;
I assent to Aristotle's example of gruel or milk
upon the fire, to this extent, that the rising and
falling of the blood does not depend upon va-
pours or exhalations, or spirits, or anything ris-
ing in a vaporous or aereal shape, nor upon any
external agency, but upon an internal prin-
ciple under the control of nature.
Nor is the heart, as some imagine, anything
like a chauffer or fire, or heated kettle, and so
the source of the heat of the blood; the blood,
instead of receiving, rather gives heat to the
heart, as it does to all the other parts of the
body; for the blood is the hottest element in
the body; and it is on this account that the
heart is furnished with coronary arteries and
veins; it is for the same reason that other parts
have vessels, viz., to secure the access of warmth
for their due conservation and stimulation; so
that the warmer any part is, the greater is its
supply of blood, or otherwise; where the blood
is in largest quantity, there also is the heat high-
est. For this reason is the heart, remarkable
through its cavities, to be viewed as the elabora-
tory, fountain, and perennial focus of heat, and
as comparable to a hot kettle, not because of its
proper substance, but because of its contained
blood; for the same reason, because they have
numerous veins or vessels containing blood, are
the liver, spleen, lungs, &c. reputed hot parts.
And in this way do I view the native or innate
heat as the common instrument of every func-
tion, the prime cause of the pulse among the
rest. This, however, I do not mean to state ab-
solutely, but only propose it by way of thesis.
Whatever may be objected to it by good and
learned men, without abusive or contemptuous
language, I shall be ready to listen to— I shall
even be most grateful to any one who will take
up and discuss the subject.
These then, are, as it were, the very ele-
ments and indications of the passage and circu-
lation of the blood, viz., from the right auricle
into the right ventricle; from the right ven-
tricle by the way of the lungs into the left
auricle; thence into the left ventricle and aorta;
whence by the arteries at large through the
pores or interstices of the tissues into the veins,
and by the veins back again with great rapidity
to the base of the heart.
There is an experiment on the veins by which
any one that chooses may convince himself of
this truth: let the arm be bound with a moder-
ately tight bandage, and then, by opening and
shutting the hand, make all the veins to swell as
much as possible, and the integuments below
the fillet to become red; and now let the arm
and hand be plunged into very cold water, or
CIRCULATION OF THE BLOOD
327
mow, until the blood pent up in the veins shall
have become cooled down; then let the fillet be
undone suddenly, and you will perceive, by the
:old blood returning to the heart, with what
:elerity the current flows, and what an effect
it produces when it has reached the heart; so
that you will no longer be surprised that some
should faint when the fillet is undone after ve-
nesection.1 This experiment shows that the
veins swell below the ligature not with attenu-
ited blood, or with blood raised by spirits or
vapours, for the immersion in the cold water
ivould repress their ebullition, but with blood
3nly, and such as could never make its way
back into the arteries, either by open-mouthed
:ommunications or by devious passages; it
;hows, moreover, how and in what way those
ivho are travelling over snowy mountains are
sometimes stricken suddenly with death, and
3ther things of the same kind.
Lest it should seem difficult for the blood to
nake its way through the pores of the various
structures of the body, I shall add one illustra-
:ion: the same thing happens in the bodies of
:hose that are hanged or strangled, as in the arm
:hat is bound with a fillet: all the parts beyond
:he noose — the face, lips, tongue, eyes, and
:very part of the head appear gorged with blood,
swollen and of a deep red or livid colour; but
f the noose be relaxed, in whatever position
yrou have the body, before many hours have
massed you will perceive the whole of the blood
:o have quitted the head and face, and gravitat-
:d through the pores of the skin, flesh, and
3ther structures, from the superior parts to-
wards those that are inferior and dependent, un-
il they become tumid and of a dark colour.
But if this happens in the dead body, with the
blood dead and coagulated, the frame stif-
ened with the chill of death, the passages all
:ompressed or blocked up, it is easy to per-
reive how much more apt it will be to occur in
•he living subject, when the blood is alive and
•eplete with spirits, when the pores are all open,
:he fluid ready to penetrate, and the passage in
:very way made easy.
When the ingenious and acute Descartes
'whose honourable mention of my name de-
nands my acknowledgments) and others, hav-
ng taken out the heart of a fish, and put it on a
jlate before them, see it continuing to pulsate
'in contracting), and when it raises or erects it-
self and becomes firm to the touch, they think
t enlarges, expands, and that its ventricles
1 Sec Chapter 1 1 , of the Disquisition on the Motion of
he Heart and Blood.
thence become more capacious. But, in my
opinion, they do not observe correctly; for, at
the time the heart gathers itself up, and be-
comes erect, it is certain that it is rather less-
ened in every one of its dimensions; that it is in
its systole, in short, not in its diastole. Neither,
on the contrary, when it collapses and sinks
down, is it then properly in its state of diastole
and distension, by which the ventricles become
more capacious. But as we do not say that the
heart is in the state of diastole in the dead
body, as having sunk relaxed after the systole,
but is then collapsed, and without all motion —
in short, is in a state of rest, and not distended.
It is only truly distended, and in the proper
state of diastole, when it is filled by the charge
of blood projected into it by the contraction of
the auricles; a fact which sufficiently appears in
the course of vivisections. Descartes, therefore,
does not perceive how much the relaxation and
subsidence of the heart and arteries differ from
their distension or diastole; and that the
cause of the distension, relaxation, and con-
striction is not one and the same; as contrary ef-
fects so must they rather acknowledge con-
trary causes; as different movements they must
have different motors; just as all anatomists
know that the flexion and extension of an ex-
tremity are accomplished by opposite antago-
nist muscles, and contrary or diverse motions are
necessarily performed by contrary and diverse
organs instituted by nature for the purpose.
Neither do I find the efficient cause of the pulse
aptly explained by this philosopher, when with
Aristotle he assumes the cause of the systole to
be the same as that of the diastole, viz., an ef-
fervescence of the blood due to a kind of ebulli-
tion. For the pulse is a succession of sudden
strokes and quick percussions; but we know of
no kind of fermentation or ebullition in which
the matter rises and falls in the twinkling of an
eye; the heaving is always gradual where the
subsidence is notable. Besides, in the body of a
living animal laid open, we can with our eyes
perceive the ventricles of the heart both charged
and distended by the contraction of the auri-
cles, and more or less increased in size accord-
ing to the charge; and, further, we can see that
the distension of the heart is rather a violent
motion, the effect of an impulsion, and not
performed by any kind of attraction.
Some are of opinion that, as no kind of im-
pulse of the nutritive juices is required in vege-
tables, but that these are attracted by the parts
which require them, and flow in to take the
place of what has been lost; so neither is there
328
WILLIAM HARVEY
any necessity for an impulse in animals, the
vegetative faculty in both working alike. But
there is a difference between plants and ani-
mals. In animals, a constant supply of warmth
is required to cherish the members, to main-
tain them in life by the vivifying heat, and
to restore parts injured from without. It is
not merely nutrition that has to be provided
for.
So much for the circulation; any impedi-
ment, or perversion or excessive excitement of
which, is followed by a host of dangerous dis-
eases and remarkable symptoms: in connexion
with the veins— varices, abscesses, pains, hem-
orrhoids, hemorrhages; in connexion with the
arteries— enlargements, phlegmons, severe and
lancinating pains, aneurisms, sarcoses, fluxions,
sudden attacks of suffocation, asthmas, stupors,
apoplexies, and innumerable other affections.
But this is not the place to enter on the con-
sideration of these; neither may I say under
what circumstances and how speedily some of
these diseases, that are even reputed incurable,
are remedied and dispelled, as if by enchant-
ment. I shall have much to put forth in my
Medical Observations and Pathology, which, so
far as I know, has as yet been observed by no one.
That I may afford you still more ample satis-
faction, most learned Riolanus, as you do not
think there is a circulation in the vessels of the
mesentery, I shall conclude by proposing the
following experiment: throw a ligature around
the porta close to the liver, in a living animal,
which is easily done. You will forthwith per-
ceive the veins below the ligature swelling in
the same way as those of the arm when the
bleeding fillet is bound above the elbow; a cir-
cumstance which will proclaim the course of
the blood there. And as you still seem to think
that the blood can regurgitate from the veins
into the arteries by open anastomoses, let the
vena cava be tied in a living animal near the
divarication of the crural veins, and immediate-
ly afterwards let an artery be opened to give is-
sue to the blood: you will soon observe the
whole of the blood discharged from all the
veins, that of the ascending cava among the
number, with the single exception of the crural
veins, which will continue full; and this cer-
tainly could not happen were there any retro-
grade passage for the blood from the veins to
the arteries by open anastomoses.
Anatomical Exercises on the Generation
of Animals
To THE LEARNED AND ILLUSTRIOUS THE PRESIDENT AND FELLOWS
OF THE COLLEGE OF PHYSICIANS OF LONDON
HARASSED with anxious, and in the end not much
availing cares, about Christmas last, I sought to
rid my spirit of the cloud that oppressed it, by
a visit to that great man, the chief honour and
ornament of our College, Dr. William Harvey,
then dwelling not far from the city. I found
him, Democritus-hke, busy with the study of
natural things, his countenance cheerful, his
mind serene, embracing all within its sphere. I
forthwith saluted him, and asked if all were
well with him? "How can it," said he, "whilst
the Commonwealth is full of distractions, and I
myself am still in the open sea? And truly," he
continued, "did I not find solace in my studies,
and a balm for my spirit in the memory of my
observations of former years, I should feel little
desire for longer life. But so it has been, that
this life of obscurity, this vacation from public
business, which causes tedium and disgust to so
many, has proved a sovereign remedy to me."
I answering said, "I can readily account for
this: whilst most men are learned through oth-
ers' wits, and under cover of a different diction
and a new arrangement, vaunt themselves on
things that belong to the ancients, thou ever
interrogatest nature herself concerning her mys-
teries. And this line of study as it is less likely
to lead into error, so is it also more fertile in en-
joyment, inasmuch as each particular point ex-
amined often leads to others which had not be-
fore been surmised. You yourself, I well remem-
ber, informed me once that you had never dis-
sected any animal — and many and many a one
have you examined — but that you discovered
something unexpected, something of which you
were formerly uninformed."
"It is true," said he: "the examination of the
bodies of animals has always been my delight;
and I have thought that we might thence not
only obtain an insight into the lighter mysteries
of nature, but there perceive a kind of image
or reflex of the omnipotent Creator himself.
And though much has already been made out
by the learned men of former times, I have still
thought that much more remained behind, hid-
den by the dusky night of nature, uninterro-
gated; so that I have oftentimes wondered and
even laughed at those who have fancied that
everything had been so consummately and ab-
solutely investigated by an Aristotle or a Galen,
or some other mighty name, that nothing could
by possibility be added to their knowledge.
Nature, however, is the best and most faithful
interpreter of her own secrets; and what she
presents either more briefly or obscurely in one
department, that she explains more fully and
clearly in another. No one indeed has ever
rightly ascertained the use or function of a part
who has not examined its structure, situation,
connexions by means of vessels, and other acci-
dents, in various animals, and carefully weighed
and considered all he has seen. The ancients,
our authorities in science, even as their knowl-
edge of geography was limited by the bounda-
ries of Greece, so neither did their knowledge
of animals, vegetables, and other natural objects
extend beyond the confines of their country.
But to us the whole earth lies open, and the
zeal of our travellers has made us familiar not
only with other countries and the manners and
customs of their inhabitants, but also with the
animals, vegetables, and minerals that are met
with in each. And truly there is no nation so
barbarous which has not discovered something
for the general good, whether led to it by acci-
dent or compelled by necessity, which had been
overlooked by more civilized communities.
But shall we imagine that nothing can accrue
to the wide domains of science from such ad-
vantages, or that all knowledge was exhausted
by the first ages of the world ? If we do, the
blame very certainly attaches to our indolence,
nowise to nature.
"To this there is another evil added: many
329
33<>
WILLIAM HARVEY
persons, wholly without experience, from the
presumed verisimilitude of a previous opinion,
are often led by and by to speak of it boldly, as
a matter that is certainly known; whence it
comes, that not only are they themselves de-
ceived, but that they likewise lead other in-
cautious persons into error."
Discoursing in this manner, and touching up-
on many topics besides with wonderful fluency
and facility, as is his custom, I interposed by
observing, "How free you yourself are from the
fault you indicate all know who are acquainted
with you; and this is the reason wherefore the
learned world, who are aware of your unwearied
industry in the study of philosophy, are eagerly
looking for your further experiments."
"And would you be the man," said Harvey,
smiling, "who should recommend me to quit
the peaceful haven, where I now pass my life,
and launch again upon the faithless sea? You
know full well what a storm my former lucu-
brations raised. Much better is it oftentimes to
grow wise at home and in private, than by pub-
lishing what you have amassed with infinite la-
bour, to stir up tempests that may rob you of
peace and quiet for the rest of your days."
"True," said I; "it is the usual reward of vir-
tue to have received ill for having merited well.
But the winds which raised those storms, like
the northwestern blast, which drowns itself in
its own rain, have only drawn mischief on
themselves."
Upon this he showed me his Exercises on the
Generation of Animals, a work composed with
vast labour and singular care; and having it in
my hands, I exclaimed, "Now have I what I
so much desired! and unless you consent to
make this work public, I must'say that you will
be wanting both to your own fame and to the
public usefulness. Nor let any fear of further
trouble in the matter induce you to withhold it
longer: I gladly charge myself with the whole
business of correcting the press."
Making many difficulties at first, urging,
among other things, that his work must be held
imperfect, as not containing his investigations
on the generation of insects, I nevertheless pre-
vailed at length, and he said to me, "I intrust
these papers to your care with full authority
either speedily to commit them to the press, or
to suppress them till some future time." Having
returned him many thanks, I bade him adieu,
and took my leave, feeling like another Jason
laden with the Golden Fleece. On returning
home I forthwith proceeded to examine my
prize in all its parts, and could not but wonder
with myself that such a treasure should have
lain so long concealed; and that whilst others
produce their trifles and emptinesses with much
ado, their messes twice, aye, an hundred times,
heated up, our Harvey should set so little store
by his admirable observations. And indeed, so
often as he has sent forth any of his discoveries
to the world, he has not comported himself like
those who, when they publish, would have us
believe that an oak had spoken, and that they
had merited the rarest honours — a draught of
hen's milk at the least. Our Harvey rather
seems as though discovery were natural to him,
a thing of ease and of course, a matter of ordi-
nary business; though he may nevertheless have
expended infinite labour and study on his works.
And we have evidence of his singular candour
in this, that he never hostilely attacks any pre-
vious writer, but ever courteously sets down
and comments upon the opinions of each; and
indeed he is wont to say that it is argument of
an indifferent cause when it is contended for
with violence and distemper; and that truth
scarce wants an advocate.
It would have been easy for our illustrious
colleague to have woven the whole of this web
from materials of his own; but to escape the
charge of envy, he has rather chosen to take
Aristotle and Fabricius of Aquapendente as his
guides, and to appear as contributing but his
portion to the general fabric. Of him, whose
virtue, candour, and genius are so well known
to you all, I shall say no more, lest I should
seem to praise to his face one whose singular
worth has exalted him beyond the reach of all
praise. Of myself I shall only say that I have
done no more than perform the midwife's office
in this business, ushering into the light this
product of our colleague's genius as you see it,
consummate and complete, but long delayed,
and fearing perchance some envious blast: in
other words, I have overlooked the press; and as
our author writes a hand which no one without
practice can easily read (a thing that is common
among our men of letters), I have taken some
pains to prevent the printer commit ting any very
grave blunders through this — a point which I
observe not to have been sufficiently attended to
in the small work of his which lately appeared.
Here then, my learned friends, you have the
cause of my addressing you at this time, viz^
that you may know that our Harvey presents
an offering to the benefit of the republic of let-
ters, to your honour, to his own eternal fame.
Farewell, and prosper.
GEORGE ENT
ANIMAL GENERATION
33'
INTRODUCTION
IT will not, I trust, be unwelcome to you, can-
did reader, if I yield to the wishes, I might even
say the entreaties, of many, and in these Exer-
cises on Animal Generation, lay before the stu-
dent and lover of truth what I have observed
on this subject from anatomical dissections,
which turns out to be very different from any-
thing that is delivered by authors, whether
philosophers or physicians.
Physicians, following Galen, teach that from
the semen of the male and female mingled in
coition the offspring is produced, and resembles
one or other, according to the predominance of
this one or of that; and, further, that in virtue
of the same predominance, it is either male or
female. Sometimes they declare the semen mas-
culinum as the efficient cause, and the semen
feminmum as supplying the matter; and some-
times, again, they advocate precisely the oppo-
site doctrine. Aristotle, one of Nature's most
diligent inquirers, however, affirms the prin-
ciples of generation to be the male and the fe-
male, she contributing the matter, he the form;
and that immediately after the sexual act the
vital principle and the first particle of the fu-
ture foetus, viz., the heart, in animals that have
red blood, are formed from the menstrual blood
in the uterus.
But that these are erroneous and hasty con-
clusions is easily made to appear: like phantoms
of darkness they suddenly vanish before the
light of anatomical inquiry. Nor is any long
refutation necessary where the truth can be
seen with one's proper eyes; where the inquirer
by simple inspection finds everything in con-
formity with reason; and where at the same
time he is made to understand how unsafe, how
base a thing it is to receive instruction from
others' comments without examination of the
objects themselves, the rather as the book of
Nature lies so open and is so easy of consultation.
What I shall deliver in these my Exercises on
Animal Generation I am anxious to make pub-
licly known, not merely that posterity may
there perceive the sure and obvious truth, but
further, and especially, that by exhibiting the
method of investigation which I have followed,
I may propose to the studious a new and, unless
I mistake, a safer way to the attainment of
knowledge.
For although it is a new and difficult road in
studying nature, rather to question things them-
selves than, by turning over books, to discover
the opinions of philosophers regarding them,
still it must be acknowledged that it is the more
open path to the secrets of natural philosophy,
and that which is less likely to lead into error.
Nor is there any just cause wherefore the la-
bour should deter anyone, if he will but think
that he himself only lives through the ceaseless
working of his heart. Neither, indeed, would
the way I propose be felt as so barren and lonely,
but for the custom, or vice rather, of the age
we live in, when men, inclined to idleness, pre-
fer going wrong with the many, to becoming
wise with the few through dint of toil and out-
lay of money. The ancient philosophers, whose
industry even we admire, went a different way
to work, and by their unwearied labour and
variety of experiments, searching into the na-
ture of things, have left us no doubtful light to
guide us in our studies. In this way it is that
almost everything we yet possess of note or
credit in philosophy, has been transmitted to
us through the industry of ancient Greece. But
when we acquiesce in the discoveries of the
ancients, and believe (which we are apt to do
through indolence) that nothing further re-
mains to be known, we suffer the edge of our
ingenuity to be taken off, and the lamp which
they delivered to us to be extinguished. No one
of a surety will allow that all truth was en-
grossed by the ancients, unless he be utterly
ignorant (to pass by other arts for the present)
of the many remarkable discoveries that have
lately been made in anatomy, these having
been principally achieved by individuals who,
either intent upon some particular matter, fell
upon the novelty by accident, or (and this is
the more excellent way) who, following the
traces of nature with their own eyes, pursued
her through devious but most assured ways till
they reached her in the citadel of truth. And
truly in such pursuits it is sweet not merely to
toil, but even to grow weary, when the pains of
discovering are amply compensated by the
pleasures of discovery. Eager for novelty, we
are wont to travel far into unknown countries
that, with our own eyes, we may witness what
we have heard reported as having been seen by
others, where, however, we for the most part
find
minuit prxsentia famam :
that the presence lessens the repute. It were
disgraceful, therefore, with this most spacious
and admirable realm of nature before us, and
where the reward ever exceeds the promise, did
we take the reports of others upon trust, and go
on coining crude problems out of these, and on
332
WILLIAM HARVEY
them hanging knotty and captious and petty
disputations. Nature is herself to be addressed;
the paths she shows us are to be boldly trodden;
for thus, and whilst we consult our proper
senses, from inferior advancing to superior lev-
els, shall we penetrate at length into the heart
of her mystery.
Of the Manner and Order of acquiring Knowl-
edge
Although there is but one road to science,
that, to wit, in which we proceed from things
more known to things less known, from mat-
ters more manifest to matters more obscure;
and universals are principally known to us,
science springing by reasonings from universals
to particulars; still the comprehension of uni-
versals by the understanding is based upon the
perception of individual things by the senses.
Both of Aristotle's propositions, therefore, are
true: first, the one in his Physics,1 where he says,
"The way is naturally prepared, from those
things that are more obvious and clear to us, to
those things that are more obvious and clear by
nature. For, indeed, the same things are not
both known to us and extant simply: whence it
is indispensable to proceed in this way, viz.,
from those things that are of a more obscure
nature, but to us are more apparent, to those
that are of a nature more obvious and distinct.
Now those things are, in the first instance,
more perspicuous and manifest to us that are
most confused in fact; whence it is necessary to
proceed from universals to particulars; for the
whole, according to the dictates of sense, is the
more obvious; and the universal is a certain
whole." And again, that other in his Analytics?
where he thus expresses himself: "Singulars are
to us more known, and are the first that exist
according to the information of sense; for, in-
deed, there is nothing in the understanding
which was not first in the sense. And although
that reasoning is naturally prior and more
known which proceeds by syllogism, still is
that more perspicuous to us which is based on
induction. And, therefore, do we more readily
define singulars than universals, for there is
more of equivocation in universals: whence it is
advisable from singulars to pass to universals."
All this agrees with what we have previously
said, although at first blush it may seem con-
tradictory; inasmuch as universals are first im-
bibed from particulars by the senses, and in so
far are only known to us as an universal is a cer-
1 Book i, i.
* Posterior Analytics, 1,2.
tain whole and indistinct thing, and a whole is
known to us according to sense. For though in
all knowledge we begin from sense, because, as
the philosopher quoted has it, sensible particu-
lars are better known to sense, still the sensa-
tion itself is an universal thing. For, if you ob-
serve rightly, although in the external sense the
object perceived is singular, as, for example, the
colour which we call yellow in the eye, still
when this impression comes to be made an
abstraction, and to be judged of and under-
stood by the internal sensorium, it is an uni-
versal. Whence it happens that several persons
abstract several species, and conceive different
notions, from viewing the same object at the
same time. This is conspicuous among poets
and painters, who, although they contemplate
one and the same object in the same place at
the same moment, and with all other circum-
stances agreeing, nevertheless regard and de-
scribe it variously, and as each has conceived or
formed an idea of it in his imagination. In the
same way, the painter having a certain portrait
to delineate, if he draw the outline a thousand
times, he will still give a different face, and each
not only differing from the other, but from the
original countenance; with such slight variety,
however, that looking at them singly, you shall
conceive you have still the same portrait set
before you, although, when set side by side, you
perceive how different they are. Now the rea-
son is this: that in vision, or the act of seeing
itself, each particular is clear and distinct; but
the moment the object is removed, as it is by
merely shutting the eyes, when it becomes an
abstraction in the fancy, or is only retained in
the memory, it appears obscure and indistinct;
neither is it any longer apprehended as a partic-
ular, but as a something that is common and
universal. Seneca explains this subtlety, accord-
ing to Plato's views, in very elegant terms: "An
idea," he says, "is an eternal copy of the things
that have place in nature. I add an explanation
of this definition, that the matter may be made
plainer to you. I desire to take your portrait;
I have you as the prototype of the picture,
from which my mind takes a certain impression
which it transfers to the canvass. The counte-
nance, therefore, which teaches and directs me,
and from which the imitation is sought, is the
idea."3 A little farther on he proceeds: "I have
but just made use of the image which a painter
forms in his mind, by way of illustration. Now,
if he would paint a likeness of Virgil, he forms
an intuitive image of his subject: the idea is the
8 Letter 58.
ANIMAL GENERATION
333
face of Virgil, the type of his future work; and
this which the artist conveys and transfers to
his work is the resemblance or portrait. What
difference is there? you ask: the one is the pat-
tern or prototype, the other the form taken
from the pattern and fixed in the work; the
artist imitates the one, he creates the other. A
statue has a certain expression of face; this is
the eidos, the species or representation; the
prototype himself has a certain expression,
which the statuary conceiving, transfers to his
statue: this is the idea. Do you desire yet an-
other illustration of the distinction ? The eidos
is in the work; the idea without the work, and
not only without the work, but it even existed
before the work was begun.'* For the things
that have formerly been noted, and that by
use or wont have become firmly fixed in the
mind of the artist, do, in fact, constitute art
and the artistic faculty; art, indeed, is the rea-
son of the work in the mind of the artist. On
the same terms, therefore, as art is attained to,
is all knowledge and science acquired; for as art
is a habit with reference to things to be done,
so is science a habit in respect of things to be
known: as that proceeds from the imitation
of types or forms, so this proceeds from the
knowledge of natural things. Each has its
origin in sense and experience, and it is im-
possible that there can rightly be either art or
science without visible instance or example. In
both, that which we perceive in sensible ob-
jects differs from the image itself which we re-
tain in our imagination or memory. That is the
type, idea, forma informans; this is the imita-
tion, the eidos, the abstract species. That is a
thing natural, a real entity; this a representa-
tion or similitude, and a thing of the reason.
That is occupied with the individual thing, and
itself is single and particular; this is a certain
universal and common thing. That in the artist
and man of science is a sensible thing, clearer,
more perfect; this a matter of reason and more
obscure: for things perceived by sense are more
assured and manifest than matters inferred by
reason, inasmuch as the latter proceed from
and are illustrated by the former. Finally, sen-
sible things are of themselves and antecedent;
things of intellect, however, are consequent,
and arise from the former, and, indeed, we can
in no way attain to them without the help of
the others. And hence it is, that without the
due admonition of the senses, without frequent
observation and reiterated experiment, our
mind goes astray after phantoms and appear-
ances. Diligent observation is, therefore, req-
uisite in every science, and the senses are fre-
quently to be appealed to. We are, I say, to
strive after personal experience, not to rely on
the experience of others; without which, in-
deed, no one can properly become a student of
any branch of natural science, nor show him-
self a competent judge of what I am about to
say on the subject of generation; for without
experience and skill in anatomy, he would not
better understand me than could one born
blind appreciate the nature and difference of
colours, or one deaf from birth judge of sounds.
I would, therefore, have you, gentle reader, to
take nothing on trust from me concerning the
generation of animals; I appeal to your own
eyes as my witnesses and judge. For as all true
science rests upon those principles which have
their origin in the operation of the senses, par-
ticular care is to be taken that by repeated dis-
section the grounds of our present subject be
fully established. If we do otherwise, we shall
but come to empty and unstable opinions; solid
and true science will escape us altogether: just
as commonly happens to those who form their
notions of distant countries and cities, or who
pretend to get a knowledge of the parts of the
human body, from drawings and engravings,
which but too frequently present things under
false and erroneous points of view. And so it is,
that in the present age we have an abundance
of writers and pretenders to knowledge, but
very few who are really learned and philoso-
phers.
Thus much have I thought good, gentle
reader, to present to you, by way of preface,
that understanding the nature of the assistance
to which I have trusted, and the counsel by
which I have been led in publishing these my
observations and experiments; and that you
yourself in passing over the same ground, may
not merely be in a condition to judge between
Aristotle and Galen, but, quitting subtleties
and fanciful conjectures, embracing nature
with your own eyes, that you may discover
many things unknown to others, and of great
importance.
Of the same matters, according to Aristotle
There is no such thing as innate knowledge,
according to Aristotle; neither opinion, nor art,
nor understanding, nor speech, nor reason it-
self, inhere in us by nature and from our birth;
but all of these, as well as the qualities and habi-
tudes, which are believed to be spontaneous,
and to lie under the control of our will, are to
be regarded as among the number of those
334
WILLIAM HARVEY
things that reach us from without according to
nature: such as the virtues and the vices, for
which men are either praised and rewarded or
reproved and punished. All our knowledge,
therefore, of every kind has to be acquired. But
this is not the place to inquire into the first
principles of knowledge.
I believe, however, that it will not be useless
if I premise a few words as to whence and how
our knowledge reaches us, both with a view to
rendering what I shall say on the subject of gen-
eration more readily intelligible, and of remov-
ing any doubts that may arise out of this opin-
ion of the Stagirite,1 who asserts that all doc-
trine and discipline based on reason are derived
from antecedent knowledge; whence it seems
to follow that there is either no first knowledge,
or that this must be innate, a conclusion which
is in contradiction with what has already been
stated.
The doubt, however, is by and by resolved
by Aristotle2 himself, when he treats of the
mode in which knowledge is acquired: for after
he has taught that all certain knowledge is ob-
tained through syllogism and demonstration,
and made it manifest that every demonstrative
syllogism proceeds from true and necessary first
principles; he goes on to inquire how principles
become known, and what the faculty is that
knows; at the same time, too, he discusses the
question: whether habits, if not innate, are en-
gendered; and whether, being innate, they lie
concealed? "We have not," he says, "these
habits; for it happens that they are concealed
from those who acquire the most admirable
kinds of knowledge through demonstration. If,
however, we receive them, not having had
them previously, how should we become in-
formed, how learn from non-antecedent knowl-
edge? It is obvious, therefore, that they are
neither possessed, nor can they be engendered
in the ignorant and those who are endowed
with no habit. Whence it is essential that some
faculty be possessed, not, however, any which
were more excellent, more exquisite than they.
Now it seems a thing common to all animals
that they have a congenital power of judging,
which we call sense. Since sense is innate, then,
the things perceived by sense remain in some
animals; in others they do not remain. Those in
whom they do not remain, however, have
either no knowledge at all, or at least none be-
yond the simple perception of the things which
do not remain; others, again, when they per-
1 Posterior Analytics, I. i.
*lbid, n. 19.
ceive, retain a certain something in their soul.
Now, as there are many animals of this descrip-
tion, there is already a distinction between one
animal and another; and to this extent, that in
some there is reason from the memory of things;
and in others there is none. Memory, therefore,
as is said, follows from sense; but from repeated
recollection of the same thing springs expe-
rience (for repeated acts of memory constitute a
single experience). From experience, however,
or from the whole and universal stored quietly
in the mind (one, to wit, in place of a multitude
— because in the whole crowd of particulars
there is one and the same universal), is derived
the principle of art and of science: of art, if it
belong to production (/'. e., action); of science,
if it belong to that which is (/'. e., the knowl-
edge of entity). Consequently, there are neither
any definite habits that are innate, nor any
habits that are formed from other and more
known habits, but from sense."
From which words of Aristotle it plainly ap-
pears by what order or method any art or science
is acquired, viz., the thing perceived by sense
remains; from the permanence of the thing per-
ceived results memory; from multiplied mem-
ory, experience; from experience, universal rea-
son, definitions, and maxims or common axi-
oms, the most certain principles of knowledge;
for example, the same thing under like condi-
tions cannot be and not be; every affirmation
or negation is either true or false; and so on.
Wherefore, as we have said above, there is
no perfect knowledge which can be entitled
ours, that is innate; none but what has been ob-
tained from experience, or derived in some way
from our senses; all knowledge, at all events, is
examined by these, approved by them, and
finally presents itself to us firmly grounded
upon some preexisting knowledge which we
possessed: because without memory there is no
experience, which is nothing else than reiter-
ated memory; in like manner memory cannot
exist without endurance of the things per-
ceived, and the thing perceived cannot remain
where it has never been.
The supreme dictator in philosophy again
and elsewhere expresses himself very elegantly
in the same direction: "All men desire by na-
ture to know; the evidence of this is the pleas-
ure they take in using their senses, among
which the sight is that which is particularly
preferred, because this especially serves us to
acquire knowledge, and informs us of the great-
est number of differences. Nature, therefore,
endowed animals with sense; some of them,
ANIMAL GENERATION
335
however, have no memory from the operations
of their senses; others, again, have memory;
and this is the reason wherefore some are more
intelligent, and some more capable of receiving
instruction than others, those, namely, that
want recollection. Some show discretion inde-
pendently of tuition: inasmuch as there are
many that do not hear, such as bees and others
of the same kind. But all animals which along
with memory have the faculty of hearing are
susceptible of education. Other creatures,
again, live possessed of fancy and memory, but
they have little store of experience; the human
kind, however, have both art and reasoning.
Now experience comes to man through mem-
ory; for many memories of the same thing have
the force of a single experience: so that expe-
rience appears to be almost identical with cer-
tain kinds of art and science; and, indeed, men
acquire both art and science by experience: for
experience, as Polus1 rightly remarks, begets
art, inexperience is waited on by accident."2
By this he plainly tells us that no one can
truly be entitled discreet or well-informed, who
does not of his own experience, /'. <?., from re-
peated memory, frequent perception by sense,
and diligent observation, know that a thing is
so in fact. Without these, indeed, we only imag-
ine or believe, and such knowledge is rather to
be accounted as belonging to others than to us.
The method of investigating truth commonly
pursued at this time, therefore, is to be held as
erroneous and almost foolish, in which so many
inquire what others have said, and omit to ask
whether the things themselves be actually so or
not; and single universal conclusions being de-
duced from several premises, and analogies
being thence shaped out, we have frequently
mere verisimilitudes handed down to us instead
of positive truths. Whence it comes that pre-
tenders to knowledge and sophists, trimming
up the discoveries of others, changing the ar-
rangement only, or the language, and adding a
few things of no importance, audaciously send
them forth as their own, and so render philoso-
phy, which ought to be certain and perspicu-
ous, obscure and intricate. For he who reads
the words of an author and fails, through his
own senses, to obtain images of the things that
are conveyed in these words, derives not true
ideas, but false fancies and empty visions;
whence he conjures up shadows and chimeras,
and his whole theory or contemplation, which,
however, he regards as knowledge, is nothing
1 Plato in Gorgias,
8 Metaphysics, i. i.
more than a waking dream, or such a delirium
as the sick fancy engenders.
I, therefore, whisper in your car, friendly
reader, and recommend you to weigh carefully
in the balance of exact experience all that I
shall deliver in these Exercises on the Generation
of Animals; I would not that you gave credit
to aught they contain save in so far as you find
it confirmed and borne out by the unquestion-
able testimony of your own senses.
The same course is even advised by Aristotle,
who, after having gone over a great many par-
ticulars about bees, says at length: "That the
generation of bees takes place in this way ap-
pears both from reason and from those things
that are seen to occur in their kind. Still all the
incidents have not yet been sufficiently exam-
ined. And when the investigation shall be com-
plete, then will sense be rather to be trusted
than reason ; reason, however, will also deserve
credit, if the things demonstrated accord with
the things that are perceived by sense."3
Of the Method to be pursued in studying
Generation
Since in animal generation (and, indeed, in
all other subjects upon which information is de-
sired) inquiry must be begun from the causes,
especially the material and efficient ones, it ap-
pears advisable to me to look back from the
perfect animal, and to inquire by what process
it has arisen and grown to maturity, to retrace
our steps, as it were, from the goal to the start-
ing place; so that when at last we can retreat no
farther, we shall feel assured that we have at-
tained to the principles; at the same time we
shall perceive from what primary matter, and
from what efficient principle, and in what way
from these the plastic force proceeds; as also
what processes nature brings into play in the
work. For primary and more remote matter, by
abstraction and negation (being stripped of its
garments, as it were), becomes more conspicu-
ous; and whatever is first formed or exists pri-
marily in generation is the material cause of
everything that succeeds. For example, before
a man attains to maturity, he was a boy, an in-
fant, an embryo. And then it is indispensable to
inquire further as to what he was in his moth-
er's womb before he was an embryo or foetus;
whether made up of three bubbles, or a shape-
less mass, or a conception or coagulum proceed-
ing from the mingled seminal fluids ot his par-
ents, or what else, as we have it delivered to us
by writers. In like manner, before a fowl had
3 On the Generation of Animals , in. 10.
336
WILLIAM HARVEY
attained to maturity or perfection — because
capable of engendering its like— it was a chicken ;
previous to which it was an embryo or foetus in
the egg; and before this, Hieronymus Fabricius
of Aquapendente, has observed rudiments of
the head, eyes, and spine. But when he asserts
that the bones are formed before the muscles,
heart, liver, lungs, and precordial parts, and
contends that all the internal organs must exist
before the external ones, he follows probabili-
ties according to previous notions rather than
inspection; and quitting the evidences of sense
that rest on anatomy, he seeks refuge in reason-
ings upon mechanical principles; a procedure
that is anything but becoming in a great anato-
mist, whose duty it was faithfully to narrate the
changes he observed taking place day by day in
the egg, up to the period when the foetus is per-
fected; and this the rather as he expressly pro-
posed to himself to write the history of the
formation of the chick in the egg, and to ex-
hibit in figures what happens in the course of
each successive day. It would have been in har-
mony with such a design, I say, had we been
informed, on the testimony of the senses, of
what parts are formed first, together, or sub-
sequently in the egg; and not had mere opin-
ions or musty conjectures, and the instances
of houses and ships, adduced in illustration
of the order and mode of formation of the
parts.
We, therefore, in conformity with the method
proposed, shall show in the first place in the
egg, and then in the conceptions of other ani-
mals, what parts are first, and what are sub-
sequently formed by the great God of Nature
with inimitable providence and intelligence,
and most admirable order. Next we shall in-
quire into the primary matter out of which,
and the efficient cause by which generation is
accomplished, and also the order and economy
of generation, as observed by us; that from
thence, from its own work, we may have some
certain information of the several faculties of
the formative and vegetative soul, and of the
nature of the soul itself, judging from its mem-
bers or organs, and their functions.
This, indeed, cannot be done in all animals:
first, because a sufficient number of several of
these cannot be commanded; and again, be-
cause, from the small size of many, they escape
our powers of vision. It must suffice, therefore,
that this is done in some kinds which are more
familiarly known to us, and that we refer all
the rest to these as types or standards.
We have, therefore, selected those that may
tend to render our experiments more undeni-
able, viz., the larger and more perfect animals,
and that are easily within reach. For in the larger
animals all things are more conspicuous; in the
more perfect, they are also more distinct; and
in those that we can command, and that live
with us, everything is more readily examined:
we have it in our power so often as we please to
repeat our observations, and so to free them
from all uncertainty and doubt. Now, among
oviparous animals of this description, we have
the common fowl, the goose, duck, pigeon; and
then we have frogs, and serpents, and fishes;
Crustacea, testacea, and mollusca; among in-
sects, bees, wasps, butterflies, and silkworms;
among viviparous creatures, we have sheep,
goats, dogs, cats, deer, and oxen; lastly, we
have the most perfect of all animals, man.
Having studied and made ourselves familiar
with these, we may turn to the consideration of
the more abstruse nature of the vegetative soul,
and feel ourselves in a condition to understand
the method, order, and causes of generation in
animals generally; for all animals resemble one
or other of those above mentioned, and agree
with them either generally or specifically, and
are procreated in the same manner, or the mode
of their generation at least is referrible by anal-
ogy to that of one or other of them. For Nature,
perfect and divine, is ever in the same things
harmonious with herself, and as her works either
agree or differ (viz., in genus, species, or some
other proportion), so is her agency in these
(viz., generation or development) either the
same or diverse. He who enters on this new and
untrodden path, and out of the vast realm of
Nature endeavours to find the truth by means
of anatomical dissections and experiments, is
met by such a multitude of facts, and these of
so unusual an aspect, that he may find it more
difficult to explain and describe to others the
things he has seen, than he reckoned it labour
to make his observations; so many things are
encountered that require naming; such is the
abundance of matter and the dearth of words.
But if he would have recourse to metaphors,
and by means of old and familiar terms would
make known his ideas concerning the things he
has newly discovered, the reader would have
little chance of understanding him better than
if they were riddles that were propounded; and
of the thing itself, which he had never seen, he
could have no conception. But then, to have
recourse to new and unusual terms were less to
bring a torch to lighten, than to darken things
still more with a cloud: it were to attempt an
ANIMAL GENERATION
337
explanation of a matter unknown by one still
more unknown, and to impose a greater toil on
the reader to understand the meaning of words
than to comprehend the things themselves.
And so it happens that Aristotle is believed by
the inexperienced to be obscure in many places;
and on this account, perhaps, Fabricius of Aqua-
pendente rather intended to exhibit the chick
in ovo in his figures than to explain its forma-
tion in words.
Wherefore, courteous reader, be not dis-
pleased with me, if, in illustrating the history
of the egg, and in my account of the generation
of the chick, I follow a new plan, and occasion-
ally have recourse to unusual language. Think
me not eager for vainglorious fame rather than
anxious to lay before you observations that are
true, and that are derived immediately from
the nature of things. That you may not do me
this injustice, I would have you know that I
tread in the footsteps of those who have already
thrown a light upon this subject, and that,
wherever I can, I make use of their words. And
foremost of all among the ancients I follow
Aristotle; among the moderns, Fabricius of
Aquapendente; the former as my leader, the
latter as my informant of the way. For even as
they who discover new lands, and first set foot
on foreign shores, are wont to give them new
names which mostly descend to posterity, so
also do the discoverers of things and the earliest
writers with perfect propriety give names to
their discoveries. And now I seem to hear Galen
admonishing us, that we should but agree about
the things, and not dispute greatly about the
words.
On Animal Generation
EXERCISE 1. Wherefore we begin with the history
of the hen's egg
HIERONYMUS FABRICIUS of Aquapendente
(whom, as I have said, I have chosen my in-
formant of the way I am to follow), in the be-
ginning of his book on the Formation of the
Ovum and Chicly has these words: "My purpose
is to treat of the formation of the foetus in every
animal, setting out from that which proceeds
from the egg: for this ought to take precedence
of all discussion of the subject, both because
from this it is not difficult to make out Aris-
totle's views of the matter, and because his
treatise on the Formation of the Foetus from the
egg, is by far the fullest, and the subject is by
much the most extensive and difficult."
We, however, commence with the history
of the hen's egg as well for the reasons above
assigned, as because we can thence obtain cer-
tain data which, as more familiar to us, will
serve to throw light on the generation of other
animals; for as eggs cost little, and are always to
be had, we have an opportunity from them of
observing the first clear and unquestionable
commencements of generation, how nature pro-
ceeds in the process, and with what admirable
foresight she governs every part of the work.
Fabricius proceeds: "Now that the contem-
plation of the formation of the chick from the
egg is of very ample scope, appears from this
that the greater number of animals are pro-
duced from ova. Passing by almost all insects
and the whole of the less perfect animals, which
are obviously produced from eggs, the greater
number of the more perfect are also engendered
from eggs." And then he goes on to particu-
larize: "All feathered creatures; fishes likewise,
with the single exception of the whale tribes;
Crustacea, testacea, and all mollusca; among
land animals, reptiles, millepeds, and all creep-
ing things; and among quadrupeds, the entire
tribe of lizards."
We, however, maintain (and shall take care
to show that it is so) that all animals whatso-
ever, even the viviparous, and man himself not
excepted, are produced from ova; that the first
conception, from which the foetus proceeds in
338
all, is an ovum of one description or another, as
well as the seeds of all kinds of plants. Emped-
ocles, therefore, spoke not improperly of the
oviparum genus arboreum, "the egg- bearing race
of trees."1 The history of the egg is, therefore,
of the widest scope, inasmuch as it illustrates
generation of every description.
We shall, therefore, begin by showing where,
whence, and how eggs are produced; and then
inquire by what means and order and successive
steps the foetus or chick is formed and per-
fected in and from the egg.
Fabricius has these additional words: "The
foetus of animals is engendered in one case from
an ovum, in another from the seminal fluid, in
a third from putrefaction; whence some crea-
tures are oviparous, others viviparous, and yet
others, born of putrefaction or by the sponta-
neous act of nature, automatically."
Such a division as this, however, does not
satisfy me, inasmuch as all animals whatsoever
may be said in a certain sense to spring from
ova, and in another certain sense from seminal
fluid; and they are entitled oviparous, vivip-
arous, or vermiparous, rather in respect of their
mode of bringing forth than of their first forma-
tion. Even the creatures that arise spontane-
ously are called automatic, not because they
spring from putrefaction, but because they
have their origin from accident, the spontane-
ous act of nature, and are equivocally engen-
dered, as it is said, proceeding from parents un-
like themselves. And, then, certain other ani-
mals bring forth an egg or a worm as their con-
ception and semen, from which, after it has
been exposed abroad, a foetus is produced;
whence such animals are called oviparous or
vermiparous. Viviparous animals are so en-
titled because they retain and cherish their con-
ception in their interior, until from thence the
foetus comes forth into the light completely
formed and alive.
EXERCISE 2. Of the seat of generation
"Nature," says Fabricius, "was first solicitous
about the place, which she determined should
be either within or without the animal: within
1 Aristotle, On the Generation of Animals, i. 20.
ANIMAL GENERATION
339
she ordained the uterus; without, the ovum: in
the uterus the blood and seminal fluid engen-
dering; in the ovum, however, the fluids or ele-
ments of which it consists supplying pabulum
for the production of the foetus."
Now, whatever is procreated of the semen
properly so called originates and is perfected
either in the same place or in different places.
All viviparous creatures derive their origin and
have their completion in the uterus itself; but
oviparous animals, as they have their beginning
within their parents, and there become ova, so
is it beyond their parents that they are per-
fected into the fcetal state. Among oviparous
animals, however, there are some that retain
their ova till such time as they are mature and
perfect; such as all the feathered tribes, reptiles
and serpents. Others, again, extrude their se-
mina in a state still immature and imperfect, and
it is without the body of the parent that in-
crease, maturity, and perfection, are attained.
Under this head we range frogs, many kinds of
fishes, crustaceous, molluscous, and testaceous
animals, the ova of which, when first extruded,
are but beginnings, sketches, yelks which after-
wards surround themselves with whites, and at-
tracting, concocting, and attaching nutriment
to themselves, are changed into perfect seeds or
eggs. Such also are the semina of insects (called
worms by Aristotle), which, imperfect on their
extrusion and in the beginning, seek food for
themselves, upon which they are nourished,
and grow from a grub into a chrysalis: from an
imperfect into a perfect egg or seed. Birds,
however, and the rest of the oviparous tribes,
lay perfect eggs; whence without the uterus the
foetus is engendered. And it was on this account
that Fabricius admitted two seats of genera-
tion : one internal, the uterus; another external,
the ovum. But he would have had more rea-
son, in my opinion, had he called the nest, or
place where the eggs are laid, the external seat,
that, to wit, in which the extruded seed or egg
is cherished, matured, and perfected into a
foetus; for it is from the differences of this seat
that the generation of oviparous animals is
principally distinguished: And it is, indeed, a
thing most worthy of admiration to see these
creatures selecting and preparing their nests
with so much foresight, and fashioning, and
furnishing, and concealing them with such in-
imitable art and ingenuity ; so that it seems im-
perative on us to admit in them a certain spark
of the divine flame (as the poet said of bees) ;
and, indeed, we can more readily admire than
imitate their untaught art and sapience.
EXERCISE 3. Of the upper part of the hen's uterus,
or the ovary
The uterus of the fowl is divided by Fabri-
cius into the superior and inferior portions, and
the superior portion he calls the ovary.
The ovary is situated immediately beneath
the liver, close to the spine, over the descend-
ing aorta. In this situation, in the larger ani-
mals with red blood, the coeliac artery enters
the mesentery, at the origin, namely, of the
emulgent veins, or a little lower; in the situa-
tion moreover in which in the other red-
blooded and viviparous animals the vasa prse-
parantia, tending to the testes, take their ori-
gin: in the same place at which the testes of the
cock-bird are situated, there is the ovary of the
hen discovered. For some animals carry their
testicles externally; others have them within
the body, in the loins, in the space midway
from the origins of the vasa praeparantia. But
the cock has his testicles at the very origin of
these vessels, as if his spermatic fluid needed no
preparation.
Aristotle1 says that the ovum begins at the
diaphragm; "I, however," says Fabricius, "in
my treatise on Respiration have denied that the
feathered kinds have any diaphragm. The dif-
ficulty is resolved by admitting that birds are
not entirely destitute of a kind of diaphragm,
inasmuch as they have a delicate membrane in
the place of this septum, which Aristotle calls a
cincture and septum. Still they have no dia-
phragm that is muscular, and that might aid
respiration, like other animals. But, indeed,
Aristotle did not know the muscles."
Thus is the prince of philosophers accused
and excused in the same breath, his challenger
being himself not free from error; because it is
certain that Aristotle knew both the muscles,
as I have elsewhere shown, and the membranes,
which in birds are not only situated transverse-
ly in the direction of the cincture of the body,
but extended in the line of the longitudinal
direction of the belly, supplying the place of
the diaphragm and being subservient to respira-
tion, as I have shown in the clearest manner in
my disquisitions on the Respiration of Animals.
And, passing over other particulars at this time,
I shall only direct attention to the fact that
birds breathe with great freedom, and in sing-
ing also modulate their voice in the most ad-
mirable manner, their lungs all the while being
so closely connected with their sides and ribs,
that they can neither be dilated and rise, nor
1 History of Animal^ vi. 2.
340
WILLIAM HARVEY
suffer contraction in any considerable de-
gree.
The bronchia or ends of the trachea in birds,
moreover, are perforate, and open into the ab-
domen (and this is an observation which I do
not remember to have met with elsewhere), so
that the air inspired is received into and stored
up within the cells or cavities formed by the
membranes mentioned above. In the same man-
ner as fishes and serpents draw air into ample
bladders situated in the abdomen, and there
store it up, by which they are thought to swim
more lightly; and as frogs and toads, when in
the height of summer they respire more vigor-
ously assume more than the usual quantity of
air into their vesicular lungs (whence they ac-
quire so large a size), which they afterwards
freely expire, croaking all the while; so in the
feathered tribes are the lungs rather the route
and passage for respiration than its adequate
instrument.
Now, had Fabricius seen this, he would never
have denied that these membranes (with the
assistance of the abdominal muscles at all events)
could subserve respiration and perform the of-
fice of the diaphragm, which, indeed, of itself,
and without the assistance of the abdominal
muscles, were incompetent to act as an instru-
ment of respiration. And, then, the diaphragm
has another duty to perform in those creatures
in whom it is muscular or fleshy, viz., to depress
the stomach filled with food, and the intestines
distended with flatus, so that the heart and
lungs shall not be invaded, and life itself op-
pressed in its citadel. But as there was no dan-
ger of anything of this kind in birds, they have
a membranous septum, perfectly well adapted
to the purposes of respiration, so that they have
very properly been said to have a diaphragm.
And were birds even entirely without any-
thing in the shape of a diaphragm, still would
Aristotle not be liable to criticism for speaking
of the ova commencing at the septum trans-
versum, because by this title he merely indi-
cates the place where the diaphragm is usually
met with in other animals. In the same way we
ourselves say that the ovary is situated at the
origin of the spermatic vasa praeparantia, al-
though the hen has, in fact, no such vessels.
The perforations of the lungs discovered by
me (and to which I merely direct attention in
this place) are neither obscure nor doubtful,
but, in birds especially, sufficiently conspicuous,
so that in the ostrich I found many conduits
which readily admitted the points of my fin-
gers. In the turkey, fowl, and, indeed, almost
all birds, you will find that a probe passed down-
wards by the trachea makes its way out of the
lungs, and is discovered lying naked and ex-
posed in one or another of the abdominal cells.
Air blown into the lungs of these creatures with
a pair of bellows passes on with a certain force
even into the most inferior of these cells.
We may even be permitted to ask, whether
in man, whilst he lives, there is not a passage
from openings of the same kind into the cavity
of the thorax? For how else should the pus
poured out in empyema and the blood extrava-
sated in pleurisy make its escape ? In penetrating
wounds of the chest, the lungs themselves being
uninjured, air often escapes by the wound; or
liquids thrown into the cavity of the thorax,
are discharged with the expectoration. But our
views of this subject will be found fully ex-
pressed elsewhere, viz., in our disquisitions On
the Causes, Uses, and Organs of Respiration.
I return to the ovary and the upper portion
of the fowl's uterus, in which the rudiments of
the eggs are produced. These, according to
Aristotle,1 in the first instance are small, and of a
white colour; growing larger, they subsequently
become of a paler and then of a deeper yellow.
The superior uterus of Fabricius, however,
has no existence until after the hen has con-
ceived, and contains the rudiments of ova with-
in it; when it may be designated as a cluster of
papulae. And he therefore observes very prop-
erly, "The superior uterus is nothing more than
an almost infinite congeries of yelks, which ap-
pear collected as it were into a single cluster, of
a rounded form, and of every size, from that of
a grain of mustard to that almost of a walnut or
medlar. This multitude of vitelli is aggregated
and conjoined very much in the manner of a
bunch of grapes, for which reason I shall con-
stantly speak of it as the vitellarium or raceme
of yelks; a comparison which Aristotle himself
made in speaking of the soft or scaleless fishes,
when he says2 their ovary or roe is extruded
agglutinated into a kind of raceme or bunch of
grapes. And in the same way as in a bunch of
grapes the several berries are seen to be of dif-
ferent sizes, some large, some small, some of
very diminutive proportions, each hanging by
its several peduncle, so do we find precisely the
same thing in the vitellarium of the fowl."
In fishes, frogs, Crustacea, and testacea, how-
ever, matters are otherwise arranged. The ovary
1 History of Animals, vi. 2.
* On the Generation of Animals, in. 8.
ANIMAL GENERATION
or vitellary here contains ova of one uniform
size only, which being extruded increase, at-
tain maturity, and give birth to foetuses simul-
taneously. But in the ovary of the common
fowl, and almost all the rest of the oviparous
tribes, the yelks are found in various stages of
their growth, from dimensions that are scarcely
visible up to the full size. Nevertheless the eggs
of the fowl and other birds (not otherwise than
in those cases where the eggs are all engendered
and laid at the same moment) ripen their foe-
tuses under the influence of incubation in the
same nest, and produce them perfect, nearly at
the same time. In the family of the pigeons,
however (which lay and incubate no more than
two eggs in the same nest), I have observed
that all the ova crowded together in the ovary,
with the exception of a single pair, were of the
same dimensions; this pair was very much larger
than any of the others, and already prepared to
descend into the second or lower uterus. In
these creatures, therefore, the number of young
is great, not because of the multitude produced
at a time, but of the frequency with which
births take place, vtz., every month. In the
same way, among cartilaginous fishes, such as the
skates, dog-fishes, &c., two eggs only come to
maturity together, one of which descends from
the right, the other from the left corner of the
uterus into the inferior portion, where they are
cherished, and where they finally produce liv-
ing foetuses, precisely as happens among vivip-
arous animals; in the ovary, nevertheless, there
is almost infinite store of ova of various sizes —
in the ray I have counted upwards of a hundred.
The ova of the other oviparous tribes are
either perfected externally, as in the case of
fishes, or they are concocted or matured, as in
the instance of testacea, Crustacea, and spiders.
Testaceous animals lay their eggs amidst froth;
the crustaceous tribes, such as the shrimp, crab,
and lobster, bear them about with them, at-
tached to certain appendages; and the spiders
carry them about and cherish them, laid up in a
kind of purse or basket, made of their web. The
beetle rolls its eggs in dung, using its hind legs
in the operation, and buries them. Now, in all
these creatures the quantity of eggs is almost
incredibly great: in fishes they form two oblong
bladders or follicles, as may be seen in the carp,
herring, and smelt, in all of which, as there is no
uterus, but merely an ovary present, so is this
sometimes crowded with ova to such a degree
that it comes to surpass the body in bulk.
Of such ovaries of the mullet and carp, salted
and pressed, and dried in the smoke, was pre-
pared that article of food in such request among
the Greeks and old Italians (called botorcha by
the latter, &d r&ptxa, *'.*., salted eggs, by the
former) and very similar, we may presume, to
the masses which we find in the insides of our
smoked herrings, and to the compact granular
red-coloured roe of our lobsters. The article
prepared from the salted roe of the sturgeon,
which is called caviare, and resembles black
soap, is still the delight of epicures.
In those fishes that are highly prolific such a
quantity of eggs is engendered that the whole
abdomen can scarcely contain them, even when
they are first produced, still less when they
have grown to any size. In fishes, therefore,
there is no part save the ovary dedicated to
purposes of reproduction. The ova of these ani-
mals continue to grow without the body, and
do not require the protection of an uterus for
their evolution. And the ovary here appears to
bear an analogy to the testicles or vesiculae semi-
nales, not only because it is found in the same
place as the testes in the male (the testes in the
cock being situated, as we have said, close to
the origin of the cceliac artery, near the waist,
in the very same place as the ovary in the hen),
but because among fishes, in both sexes, as the
time of spawning approaches, two follicles, alike
in situation, size, and shape, are discovered, ex-
tending the whole length of the abdomen;
which increase and become distended at the
same period: in the male with a homogeneous
milky spermatic matter (whence the term milk
or milt of fishes); in the female with innumer-
able granules, which, from their diminutive
size and close texture, in the beginning of the
season, escape the powers of vision, and present
themselves as constituting an uniform body,
bearing the strongest resemblance to the milt
of the male regularly coagulated. By and by
they are seen in the guise of minute grains of
sand, adhering together within their follicles.
In the smaller birds that lay but once a year,
and a few eggs only, you will scarcely discover
any ovary. Still, in the place where the testicles
are situated in the male, there in the female,
and not less obviously than the testicles of the
male, you will perceive three or four vesicles
(the number being in proportion to that of the
eggs of which they are the rudiments), by way
of ovary.
In the cornua of the uterus of snakes (which
resemble the vasa deferentia in male animals),
the first rudiments of the ova present them-
342
WILLIAM HARVEY
selves as globules strung upon a thread, in the
same way as women's bracelets, or like a rosary
composed of amber beads.
Those ova that are found in the ovary of the
fowl consequently are not to be regarded as
perfect eggs, but only as their rudiments; and
they are so arranged on the cluster, they suc-
ceed each other in such an order and of such
dimensions, that they are always ready for each
day's laying. But none of the eggs in the ovary
are surrounded with albumen; there the yelk
exists alone, and each, as it enlarges, extricates
itself from the general congeries of smaller ones,
in order that it may the more readily find space
to grow. Fabricius, therefore, is right when he
says, "The yelks which are on the surface of the
cluster are larger than those of the middle, which
are surrounded as it were by the larger ones.
The very smallest of all the ova are situated
towards the centre."1 That is to say, those that
grow acquire larger dimensions and become de-
tached from the rest, and as this proceeds, the
several yelks, besides their tunica propria, are
invested with another from the ovary, which
embraces them externally, and connects them
with the base whence they spring. This coat is,
therefore, entitled the peduncle by Fabricius,
and its office is that of a foot-stalk, viz., to sup-
ply nourishment to the ovum, in the same way
as fruit is nourished through the stalk by which
it is connected with the tree. "For this pedun-
cle is a hollow membranous bond of union, ex-
tending from the foundation of the cluster to
the yelk, coming into contact with which, it is
dilated and expanded in the same way as the
optic nerve in the eye, and covers the vitellus
with an external tunic. This perchance was
what Aristotle called the oroXov 6^0aXoc*)5?7^,
or umbilical appendix, and described as forming
a kind of tube. This peduncle includes numer-
ous vessels, which are distributed on all sides
around the yelk."
So much is accurately related by Fabricius;
but he errs when he says, "This tunic does not
surround the entire vitellus, but only extends
upon it a little beyond the middle, very much
in the manner of an acorn within its cup; whence
it comes that the outer portion of the yelk,
which is not invested by the membrane in ques-
tion, presents itself free from vessels, and to ap-
pearance naked." The membrane, nevertheless,
surrounds the yelk completely; but on the
outer aspect it is not very easily distinguished
from the tunica propria, both of them being of
extreme delicacy. Posteriorly, however, and
1 Op. «>., p. 3.
where the yelk is turned towards the basis of
the cluster, the tunic in question does not ad-
here to the vitellus, neither does it send any
vessels to this part, but merely embraces it in
the manner of a sac.
Each vitellus receives a distinct tunic from
the ovarian basis; whence this is not to be re-
garded as the common uterus, since nothing is
discovered here except the cluster or heap of
ova, of many different sizes, proceeding from
the same foundation.
Now, this foundation or basis is a body sui
generis^ arising on the spine of the feathered
kinds, connected by means of large arteries and
veins, and of a loose, porous, and spongy tex-
ture, in order that multitudes of ova may be
produced from it, and that it may supply tunics
to all; which tunics, when the yelks have grown
to their full size, are distended by them, and
then the tunics surround the vitelli, in the man-
ner of sacks with narrower necks and more ca-
pacious bellies, very much like the flasks that
are formed by the breath of the glass-blower.
Fabricius then proceeds: "The yelks, as they
proceed from small beginnings, from the size of
millet or mustard seeds, and are at first not only
extremely small, but colourless, as Aristotle
says, so do they increase by degrees, and, ac-
cording to Aristotle, become first of a paler and
then of a deeper yellow, until they have at-
tained to the dimensions familiar to all." I,
however, have observed ova vastly smaller
than millet seeds, ova which, like papulae or
sudamma, or the finest grains of sand (such as
we have indicated as found in the roe of fishes),
almost escaped the powers of sight; their places,
indeed, were only proclaimed by a kind of
roughness of the membranes.
EXERCISE 4. Of the infundibulum
The next succeeding portion of the uterus
of the common fowl is called the infundibulum
by Fabricius. It forms a kind of funnel or tube,
extending downwards from the ovary (which
it everywhere embraces), and becoming grad-
ually wider, terminates in the superior pro-
duced portion of the uterus. This infundibu-
lum yields a passage to the yelks when they
have broken from their foot-stalks in their
descent from the ovary into the second uterus
(so it is styled by Fabricius). It resembles the
tunica vaginalis in the scrotum, and is a most
delicate membrane, very easily dilatable, fitted
to receive the yelks that are daily cast loose,
and to transmit them to the uterus men-
tioned.
ANIMAL GENERATION
343
Would you have an example of these struc-
tures? Figure to yourself a small plant, whose
tuberous roots should represent the congeries
of yelks; its stalk the infundibulum. Now, as
the stalk of this plant dies in the winter and
disappears, in like manner, when the fowl
ceases to lay eggs, the whole ovary, with the
infundibulum, withers, shrinks, and is an-
nulled; the basis and indication of the roots
being still left.
This infundibulum seems only to discharge
the office of a conduit, or tube of passage: the
yelk is never observed sticking in it; but as the
testes at times creep upwards through the tu-
nicae vaginales into the groins, and in some ani-
mals—the hare and the mole — even become
concealed within the abdomen, and neverthe-
less again descend and show themselves exter-
nally, so are the vitelli transmitted through
the infundibulum from the ovary into the ute-
rus. Its office is served, and even its form is
imitated, by the funnel which we make use of
when we pour fluids from one vessel into an-
other having a narrower mouth.
EXERCISE 5. Of the external portion of the uterus
of the common fowl
Fabricius pursues his account of the uterus
after having described the ovary, and in such
an inverse order, that he premises a descrip-
tion of the superior portion or appendage of
the uterus before he approaches the uterus it-
self. He assigns to it three turns or spirals, with
somewhat too much of precision or determin-
ateness, and settles the respective situations of
these spirals, which are nevertheless of uncer-
tain seat. Here, too, he very unnecessarily re-
peats his definition of the infundibulum. I
would, therefore, in this place, beg to be al-
lowed to give my own account of the uterus of
the fowl, according to the anatomical method,
which I consider the more convenient, and
proceeding from external to internal parts, in
opposition to the method of Fabricius.
In the fowl stripped of its feathers, the fun-
dament will be observed not contracted cir-
cularly, as in other animals, but forming a de-
pressed orifice, slit transversely, and consisting
of two lips lying over against each other, the
superior of the two covering and concealing
the inferior, which is puckered together. The
superior labium, or velabrum, as it is called,
arises from the root of the rump, and as the
upper eyelid covers the eye, so does this cover
the three orifices of the pudenda, war., the
anus, the uterus, and the ureters, which lie
concealed under the velabrum as under a kind
of prepuce; very much as in the pudenda of
the woman we have the orifice of the vulva
and the meatus urinarius concealed between
the labia and the nymphae. So that without the
use of the knife, or a somewhat forcible retrac-
tion of the velabrum in the fowl, neither the
orifice by which the faeces pass from the intes-
tines, nor that by which the urine issues from
the ureters, nor yet that by which the egg es-
capes from the uterus, can be perceived. And
as the two excrementitious discharges (the
urine and the faeces) are expelled together as
from a common cloaca, the velabrum being
raised at the time, and the respective outlets
exposed; so, during intercourse, the hen on
the approach of the cock uncovers the vulva,
and prepares for his reception, a circumstance
observed by Fabricius in the turkey hen when
she is eager for the male. I have myself ob-
served a female ostrich, when her attendant
gently scratched her back, which seemed to
excite the sexual appetite, to lie down on the
ground, lift up the velabrum, and exhibit and
protrude the vulva, seeing which the male,
straightway inflamed with a like oestrum,
mounted, one foot being kept firm on the
ground, the other set upon the back of the
prostrate female; the immense penis (you
might imagine it a neat's tongue!) vibrated
backwards and forwards, and the process of
intercourse was accompanied with much ado
in murmuring and noise — the heads of the
creatures being at the same time frequently
thrust out and retracted — and other indica-
tions of enjoyment. Nor is it peculiar to birds,
but common to animals at large, that, wagging
the tail and protruding the genital parts, they
prepare for the access of the male. And, in-
deed, the tail in the majority of animals has
almost the same office as the velabrum in the
common fowl; unless it were raised or drawn
aside, it would interfere with the discharge of
the faeces and the access of the male.
In the female red-deer, fallow-deer, roe, and
others of the more temperate animals, there is
a corresponding protection to their private
parts, a membranous velabrum covering the
vulva and meatus urinarius, which must be
raised before the penis of the male can be in-
troduced.
In animals that have a tail, moreover, par-
turition could not take place unless this part
were lifted up; and even the human female is
assisted in her labour by having the coccyx
anointed and drawn outwards with the finger.
344
WILLIAM HARVEY
A surgeon, a trustworthy man, and with
whom I am upon intimate terms, on his return
from the East Indies informed me, in perfect
sincerity, that some inland and mountainous
parts of the island of Borneo are still inhabited
by a race of caudate human beings (a circum-
stance of which we also read in Pausanias), one
of whom, a virgin, who had only been cap-
tured with great difficulty, for they live in the
vtoods, he himself had seen, with a tail, thick,
fleshy, and a span in length, reflected between
the buttocks, and covering the anus and pu-
denda: so regularly has nature willed to cover
these parts.
To return. The structure of the velabrum in
the fowl is like that of the upper eyelid; that is
to say, it is a fleshy and muscular fold of the
skin, having fibres extending from the circum-
ference on every side towards the centre; its
inner surface, like that of the eyelid and pre-
puce, being soft. Along its margin also there is
a semicircular tarsus, after the manner of that
of the eyelid; and in addition, between the
skin and fleshy membrane, an interposed car-
tilage, extending from the root of the rump,
the sickle-shaped tarsus being connected with
it at right angles (very much as we observe a
small tail comprehended between the wing on
either side, in bats). By this structure the vela-
brum is enabled more readily to open and
close the foramina pudendi that have been
mentioned.
The velabrum being now raised and re-
moved, certain foramina are brought into
view, some of which are very distinct, others
more obscure. The more obvious are the anus
and vulva, or the outlet of the faecal matters
and the inlet to the uterus. The more obscure
are, first, that by which the urine is excreted
from the kidneys, and, second, the small ori-
fice discovered by Fabricius, "into which," he
says, "the cock immits the spermatic fluid," a
foramen, however, which neither Antony
Ulm, a careful dissector, has indicated in Al-
drovandus, nor any one else except Fabricius,
so far as I know, has ever observed.
All these foramina are so close to one an-
other that they seem almost to meet in a sin-
gle cavity, which, as being common to the
faeces and urine, may be called the cloaca. In
this cavity, the urine, as it descends from the
kidneys, is mingled with the feculent matters
of the bowels, and the two are discharged to-
gether. Through this, too, the egg, as it is laid,
forces itself a passage.
Now, the arrangements in this cavity arc
such, that both excrements descending into a
common sac, the urine is made use of as a nat-
ural clyster for their evacuation. The cloaca is
therefore thicker and more rugous than the
intestine; and at the moment of laying and of
coition, it is everted (the velabrum which
covers it being raised as I have already said),
the lower portion of the bowel being as it were
prolapsed. At this moment all the foramina
that terminate in the cloaca are conspicuous;
on the return or reduction of the prolapsed
portion, however, they are concealed, being all
collected together as it were into the common
purse or pouch.
The more conspicuous foramina, those, viz.,
of the anus and uterus, are situated, with ref-
erence to one another, differently in birds
from what they are in other animals. In these
the pudendum, or female genital part, is sit-
uated anteriorly between the rectum and
bladder; in birds, however, the excrementi-
tious outlet is placed anteriorly, so that the in-
let to the uterus is situated between this and
the rump.
The foramen, into which Fabricius believes
the cock to inject his fluid, is discovered be-
tween the orifice of the vulva and the rump.
I, however, deny any such use to this foramen;
for in young chickens it is scarcely to be seen,
and in adults it is present indifferently both in
males and females. It is obvious, therefore,
that it is both an extremely small and obscure
orifice, and can have no such important func-
tion to perform: it will scarcely admit a fine
needle or a bristle, and it ends in a blind cav-
ity; neither have I ever been able to discover
any spermatic fluid within it, although Fab-
ricius asserts that this fluid is stored up there
even for a whole year, and that all the eggs
contained in the ovary may be thence fecun-
dated, as it is afterwards stated.
All birds, serpents, oviparous quadrupeds,
and likewise fishes, as may readily be seen in
the carp, have kidneys and ureters through
which the urine distils, a fact which was un-
known to Aristotle and philosophers up to this
time. In birds and serpents, which have spongy
or largely vesicular lungs, the quantity of
urine secreted is small, because they drink lit-
tle, and that by sipping; there was, therefore,
no occasion for an urinary bladder in these
creatures: the renal secretion, as already
stated, is accumulated in a common cavity
or cloaca, along with the drier intestinal ex-
crement. Nevertheless, I do find an urinary
bladder in the carp and some other fishes.
ANIMAL GENERATION
345
In the common fowl the ureters descend
from the kidneys, which are situated in long
and ample cavities on either side of the back,
to terminate in the common cavity or cloaca.
Their terminations, however, are so obscure
and so hidden by the margin of the cavity,
that to discover them from without and pass a
fine probe into them would be found impossi-
ble. Nor is this at all surprising, because in all,
even the largest animals, the insertion of the
ureters near the neck of the bladder is so tor-
tuous and obscure, that although the urine dis-
tils freely from them into the bladder, and cal-
culi even make their way out of them, still
neither fluids nor air can be made to enter
them by the use of any amount of force. On
the other hand, in birds as well as other ani-
mals, a probe or a bristle passed downwards
from the kidney towards the bladder by the
ureters, readily makes its way into the cloaca
or bladder.
These facts are particularly distinct in the
ostrich, in which, besides the external orifice
of the common cavity which the velabrum
covers, I find another within the anus, having
a round and constricted orifice, shutting in
some sort in the manner of a sphincter.
Passing by these particulars, however, let us
turn to others that bear more immediately up-
on our subject. The uterine outlet or vulva,
then, or the passage from the common cavity
to the uterus of the fowl, is a certain protuber-
ance, soft, lax, wrinkled, and orbicular, resem-
bling the orifice of the prepuce when closed, or
appearing as if formed by a prolapse of the in-
ternal membrane of the uterus. Now this outlet
is situated, as I have said, between the anus and
rump, and slightly to the left of the middle line
of the body, which Ulysses Aldrovandi imag-
ines to be for the purpose of "facilitating inter-
course, and the entrance of the genital organ of
the cock." I have myself observed, however, re-
peatedly, that the hen turned the common ori-
fice to the right or left indifferently, according
to the side from which the cock approached
her. Neither do I find any penis in the cock —
neither, indeed, could Fabricius — although in
the goose and duck it is very conspicuous. But
in its stead I discover an orifice in the cock, not
otherwise than in the hen, although it is small-
er and more contracted in her than in him; and
in the swan, goose, and duck the same thing
also appears, the penis of the male goose and
duck protruding through this orifice during
intercourse.
In a black drake I noticed the penis of such a
length that after intercourse it trailed on the
ground, and a fowl following, pecked at it
greedily, thinking it an earth-worm, as I ima-
gine, so that it was retracted more quickly
than usual.
In the male ostrich I have found within this
pudendal orifice a very large glans, and the red
body of the penis, as we discover them within
the prepuce of the horse, resembling a deer's or
a small neat's tongue in form and magnitude;
and I have frequently observed this organ, rigid
and somewhat hooked during the coitus, and
when entered into the vulva of the female, held
for some considerable time there without any
movement: it was precisely as if the two crea-
tures had been fastened together with a nail.
Meantime, by the gesticulations of their heads
and necks, and by their noises, they seemed to
notify their nuptials, and to express the great
degree of pleasure they experienced.
I have read in a treatise of Dr. Du Val, a
learned physician of Rouen, that a certain
hermaphrodite was referred to the surgeons
and accoucheurs, that they might determine
whether it were a man or a woman. They, from
an examination of the genital organs, adjudged
the party to be of the feminine gender, and a
dress in accordance with this decision was or-
dered. By and by, however, the individual was
accused of soliciting women, and of discharging
the man's office; and then it was found, that
from a prepuce, as from the private parts of a
woman, a penis protruded, and served to per-
form the male's business. I have myself occasion-
ally seen the penis of a certain man so greatly
shrunk in size, that, unless when excited, noth-
ing was visible in the wrinkled prepuce above
the scrotum but the extremity of the glans.
In the horse and some other animals, the
principal and ample length of the member is
protruded from its concealment. In the mole,
too, which is a small animal, there is a remark-
able retraction of the penis between the skin
and muscles of the belly; and the vulva in the
female of this creature is also longer and deeper
than usual.
The cock, which is without a penis, performs
copulation, as I imagine, in the same manner as
the smaller birds, among which the process is
rapidly executed, and by mere contact. The
orifices of the male and female cloaca, which at
the moment are protuberant externally, which,
especially in the male, become tense and in-
jected, like the glans penis, encounter, and coi-
tion is effected by a succession of salutes, not
by any longer intromission of parts, for I do
346 WILLIAM
not think that the organs of the cock enter
those of the hen at all.
In the copulation of horses, dogs, cats, and
the like, the female presents her organ rigid
and injected to the penis of the male. And this
also takes place in birds which, if they be tame
and suffer themselves to be handled, when in-
flamed with desire present their parts, which
will then be found resisting and hard to the
finger.
Birds are sometimes so lustful, that if you
but stroke their backs gently with your hand,
they will immediately lie down and expose and
protrude their uterine orifice; and if this part
be touched with the finger, they will not fail to
proclaim their satisfaction. And that the females
may thereby be made to lay eggs, as testified to
by Aristotle,1 1 have myself found in the case of
the blackbird, thrush, and others. I learned the
fact, indeed, in former years by accident, and
to my detriment; for my wife had a beautiful
parrot, a great pet, learned and talkative
enough, and so tame that it was allowed to
roam at liberty about the house : when its mis-
tress was absent it sought her everywhere; on
her return it caressed her, and loudly pro-
claimed its joy; when called to, it would answer;
would fly to its mistress, and then seizing her
clothes with beak and feet alternately, it
climbed to her shoulder, whence creeping down
the arm, it reached her hand, its usual seat.
When ordered to speak or to sing, it would
obey, although it were the night season and
quite dark. Full of play and lasciviousness, it
would frequently sit in its mistress's lap, where
it loved to have her scratch its head and stroke
its back, upon which, fluttering with its wings
and making a gentle noise, it testified the pleas-
ure it experienced. I believed all this to pro-
ceed from his usual familiarity and love of being
noticed; for I always regarded the creature as a
male, by reason of his proficiency in talking
and singing. For among birds, the females rarely
sing or challenge one another by their note; the
males alone solace their mates by their tuneful
warblings, and call them to the rites of love.
And it is on this account that Aristotle says,
"If partridges be placed over against the males,
and the wind blow towards them from where
the males sit, they are impregnated and con-
ceive. They even for the most part conceive
from the note of the male bird, if they be in
season and full of desire. The flight of the male
over them will also have the same effect, the
male bird casting down a fertilizing influence
1 History of 'Animals, vi. 2.
HARVEY
upon the female."2 Now this happens especially
in the spring season, whence the poet sings:
Earth teems in Spring, and craves the genial
seed.
The almighty father, ALther, then descends,
In fertilizing showers, into the lap
Of his rejoicing spouse, and mingling there
In wide embrace sustains the progeny
Innumerous that springs. The pathless woods
Then ring with the wild bird's song, and
flocks and herds
Disport and spend the livelong day in love?
Not long after the caressings mentioned, the
parrot, which had lived in health for many
years, fell sick, and by and by being seized with
repeated attacks of convulsions, seated in the
lap of its mistress, it expired, grievously re-
gretted. Having opened the body in search of
the cause of death, I discovered an egg, nearly
perfect, in the uterus, but in consequence of
the want of a male, in a state of putrefaction;
and this, indeed, frequently happens among
birds confined in cages, which show desire for
the company of the male.
These and other instances induce me to be-
lieve that the common fowl and the pheasant
do not only solace their females with their
crowing, but, further, give them the faculty of
producing eggs by its means; for when the cock
crows in the night some of the hens perched
near him bestir themselves, clapping their
wings and shaking their heads; shuddering and
gesticulating as they are wont to do after in-
tercourse.
A certain bird, as large again as a swan, and
which the Dutch call a cassowary, was imported
no long time ago from the island of Java, in the
East Indies, into Holland. Ulysses Aldrovan-
dus4 gives a figure of this bird, and informs us
that it is called an emeu by the Indians. It is
not a two-toed bird, like the ostrich, but has
three toes on each foot, one of which is fur-
nished with a spur of such length, strength, and
hardness, that the creature can easily kick
through a board two fingers' breadth in thick-
ness. The cassowary defends itself by kicking
forwards. In the body, legs, and thighs it re-
sembles the ostrich; it has not a broad bill like
the ostrich however, but one that is rounded
and black. On its head, by way qf crest, it has
an orbicular protuberant horn. It has no tongue,
and devours everything that is presented to it
1 History of Animals, v. 5; vi. 2.
* Virgil, Georgics, n.
4 Ormthol., Book xx, p. 541.
ANIMAL GENERATION
347
— stones, coals, even though alight, pieces of
glass — all without distinction. Its feathers
sprout in pairs from each particular quill, and
are of a black colour, short and slender, ap-
proaching to hair or down in their characters.
Its wings are very short and imperfect. The
whole aspect of the creature is truculent, and
it has numbers of red and blue wattles longi-
tudinally disposed along the neck.
This bird remained for more than seven years
in Holland, and was then sent, among other
presents, by the illustrious Maurice Prince of
Orange, to his Serene Majesty our King James,
in whose gardens it continued to live for a
period of upwards of five years. By and by,
however, when a pair of ostriches, male and
female, were brought to the same place, and
the cassowary heard and saw these in a neigh-
bouring inclosure, at their amours, unexpect-
edly it began to lay eggs, excited, as I imagine,
through sympathy with the acts of an allied
genus; I say unexpectedly, for all who saw the
cassowary, judging from the weapons and orna-
ments, had regarded it as a male rather than a
female. Of these eggs, one was laid entire, and
this I opened, and found it perfect: the yelk
surrounded by the white, the chalazae attached
on either side, and a small cavity in the blunt
end; there was also a cicatricula or macula alba
present; the shell was thick, hard, and strong;
and having taken off the top, I had it formed
into a cup, in the same way as ostriches' eggs are
commonly fashioned. This egg was somewhat
less than that of an ostrich, and, as I have said,
perfect in all respects. Undoubtedly, however,
it was a sort of accidental egg, and, by reason
of the absence of the male, unfruitful. I pred-
icated the death of the cassowary as likely to
happen soon when she began laying, moved to
do so by what Aristotle says: "Birds become
diseased and die unless they produce fruitful
eggs.'*1 And my prediction came true not long
afterwards. On opening the body of the casso-
wary, I discovered an imperfect and putrid egg
in the upper part of the uterus, as the cause of
its untimely death, just as I had found the same
thing in the parrot, and other instances be-
sides.
Many birds, consequently, the more sala-
cious they are, the more fruitful are they; and
occasionally, when abundantly fed, or from
some other cause, they will even lay eggs with-
out the access of the male. It rarely happens,
however, that the eggs so produced are either
perfected or laid; the birds are commonly soon
1 On the Generation of Animals, HI.
seized with serious disorders, and at length die,
The common fowl, nevertheless, not only con-
ceives eggs, but lays them, quite perfect in ap-
pearance too; but they are always wind eggs,
and incapable of producing a chick. In like
manner many insects, among the number silk-
worms and butterflies, conceive eggs and lay
them, without the access of the male, but they
are still adventitious and barren. Fishes also do
the same.
It is of the same significance in these animals
when they conceive eggs, as it is in young wom-
en when their uterus grows hot, their menses
flow, and their bosoms swell— in a word, when
they become marriageable; and who, if they
continue too long unwedded, are seized with
serious symptoms — hysterics, furor uterinus,
&c. or fall into a chachectic state, and distem-
peratures of various kinds. All animals, indeed,
grow savage when in heat, and unless they are
suffered to enjoy one another, become changed
in disposition. In like manner women occasion-
ally become insane through ungratified desire,
and to such a height does the malady reach in
some, that they are believed to be poisoned, or
moon -struck, or possessed by a devil. And this
would certainly occur more frequently than it
does, without the influence of good nurture, re-
spect for character, and the modesty that is in-
nate in the sex, which all tend to tranquillize
the inordinate passions of the mind.
EXERCISE 6. Of the uterus of the fowl
The passage from the external uterine ori-
fice to the internal parts and uterus itself,
where the egg is perfected, is by that part
which in other animals is called the vagina or
vulva. In the fowl, however, this passage is so
intricate, and its internal membrane is so loose
and wrinkled, that although there is a ready
passage from within outwards, and a large egg
makes its way through all without much diffi-
culty, still it scarcely seems likely that the
penis of the male could penetrate or the sper-
matic fluid make its way through it; for I have
found it impossible to introduce either a probe
or a bristle; neither could Fabricius pass any-
thing of the sort, and he says that he could not
even inflate the uterus with air. Whence he
was led I fancy to give an account of the uter-
us, proceeding from more internal to more ex-
ternal parts. Considering this structure of the
uterus also, he denies that the spermatic fluid
of the male can reach the cavity of the uterus,
or go to constitute any part of the egg,2 To this
1 Op. cit.t p. 31.
WILLIAM HARVEY
statement I most willingly subscribe; for, in-
deed, there is nothing in the fruitful egg which
is not also in the barren one; there is nothing
in the way of addition or change which indi-
cates that the seminal fluid of the male has
either made its way into the uterus, or come
into contact with the egg. Moreover, although
without the access of the cock all eggs Iai4 are
winded and barren, still through his influence,
and long after intercourse, fruitful eggs are de-
posited, the rudiments or matter of which did
not exist at the time of the communication.
With a view to explaining how the spermat-
ic fluid of the cock renders eggs fecund, Fab-
ricius says: "Since the semen does not appear
in the egg, and yet is thrown into the uterus
by the cock, it may be asked why this is done
if the fluid does not enter the egg? Further: if
not present in the egg, how is that egg made
fruitful by the spermatic fluid of the cock
which it yet does not contain? My opinion is
that the semen of the cock thrown into the
commencement of the uterus, produces an in-
fluence on the whole of the uterus, and at the
same time renders fruitful the whole of the
yelks, and finally of the perfect eggs which fall
into it; and this the semen effects by its pecul-
iar property or irradiative spirituous sub-
stance, in the same manner as we see other
animals rendered fruitful by the testicles and
semen. For if anyone will but bring to mind
the incredible change that is produced by cast-
ration, when the heat, strength, and fecundity
are lost, he will readily admit that what we
have proposed may happen in reference to the
single uterus of a fowl. But that it is in all re-
spects true, and that the faculty of impreg-
nating the whole of the ova, and also the ute-
rus itself, proceeds from the semen of the cock,
appears from the custom of those housewives
who keep hens at home but no cock, that they
commit their hens for a day or two to a neigh-
bour's cock, and in this short space of time
the whole of the eggs that will be laid for a
certain season are rendered prolific. And this
fact is confirmed by Aristotle,1 who will have
it that, among birds, one intercourse suffices
to render almost all the eggs fruitful. For the
fecundating influence of the seminal fluid, as it
cannot exhale, so is it long retained in the uter-
us, to which it imparts the whole of its virtue;
nature herself stores it up, placing it in a cavity
appended to the uterus, near the fundament,
furnished with an entrance only, so that, being
there laid up, its virtue is the better preserved
1 On the Generation of Animals > in, i.
and communicated to the entire uterus."2
I, however, suspected the truth of the above
views, all the more when I saw that the words
of the philosopher referred to were not accu-
rately quoted. Aristotle does not say that
"Birds which have once copulated almost all
continue to lay prolific eggs," but simply "al-
most all continue to lay eggs"; the word "pro-
lific" is an addition by Fabricius. But it is one
thing to have birds conceiving eggs after inter-
course, and another to say that these eggs are
fruitful through this intercourse. And this is
the more obvious from Aristotle's previous
words, where he says, "Nor in the family of
birds can those eggs even that are produced by
intercourse acquire their full size unless the
intercourse between the sexes be continued.
And the reason is that as the menstrual excre-
tion in women is attracted by the intercourse
of their husbands (for the uterus, being
warmed, draws the moisture, and the passages
are opened), so in birds it comes to pass that,
as the menstruous discharge takes place very
gradually, because of its being in small quan-
tity, it cannot make its way externally, but is
contained superiorly as high as the waist, and
only distils down into the uterus itself. For
the egg is increased by this, just as the foetus of
oviparous animals is nourished by that which
reaches it through the umbilicus. For when
once birds have copulated, almost all continue
to lay eggs, but of small size and imperfect";
and therefore unprolific, for the perfection of
an egg is its being fertile. If, therefore, without
continued intercourse, not even those eggs
that were conceived in consequence of inter-
course grow to their proper size, or, as Fabri-
cius interprets it, are "perfected," much less
are those eggs prolific which fowls continue to
lay independently of intercourse with the
male bird.
But lest any one should think that these
words, "for the uterus warmed, draws, and the
passages are opened," signify that the uterus
can attract the semen masculinum into its
cavity, let him be aware that the philosopher
does not say that the uterus attracts the semen
from without into its cavity, but that in fe-
males, from the veins and passages, opened by
the heat of intercourse, the menstruous blood
is attracted from its own body; so in birds the
blood is attracted to the uterus, warmed by
repeated intercourse, whereby the eggs grow,
as the foetus of oviparous animals grows
through the umbilicus.
2 Op. cit.9 p. 37.
ANIMAL GENERATION
349
But what Fabricius adds upon that cavity
or bursa, in which he thinks the semen of the
cock may be stored up for a whole year, has
been already refuted by us, where we have
stated that it contains no seminal fluid, and
that it exists in the cock as well as in the hen.
Wherefore, though I readily believed (if by
fecundity we are to understand a greater num-
ber of larger eggs) that the hens of poor peo-
ple, indifferently fed in all probability, will lay
both fewer and smaller eggs unless they have
the company of a cock; agreeably to what the
philosopher quoted avers, viz.: "that hens
which have once been trodden continue to lay
larger, better, and a greater number of eggs
through the whole of the year*' (a result on
which the abundance and the good quality of
the food has unquestionably a great influence) ;
still that hens should continue for a whole year
to lay prolific eggs after a few addresses of the
cock, appeared to me by no means probable:
for, had a small number of contacts sufficed for
the purposes of generation during so long a
period, nature, which does nothing in vain,
would have constituted the males among birds
less salacious than they are; nor should we see
the cock soliciting his hens so many times a
day, even against their inclination.
We know that the hen, as soon as she quits
the nest where she has just laid an egg, cackles
loudly, and seems to entice the cock, who on
his part crowing lustily, singles her out and
straightway treads her, which surely nature
had never permitted unless for purposes of
procreation.
A male pheasant kept in an aviary was so in-
flamed with lust, that unless he had the com-
pany of several hen-birds, six at the least, he
literally maltreated them, though his repeated
addresses rather interfered with their breeding
than promoted it. I have seen a single hen-
pheasant shut up with a cock-bird (which she
could in no way escape) so worn out, and her
back so entirely stript of feathers through his
reiterated assaults, that at length she died ex-
hausted. In the body of this bird, however, I
did not discover even the rudiments of eggs.
I have also observed a male duck, having
none of his own kind with him, but associating
with hens, inflamed with such desire that he
would follow a pullet even for several hours,
would seize her with his bill, and mounting at
length upon the creature, worn out with
fatigue, would compel her to submit to his
pleasure.
The conuncm cock, victorious in a battle,.
not only satisfies his desires upon the sultanas
of the vanquished, but upon the body of his
rival himself.
The females of some animals are likewise so
libidinous that they excite their males by
pecking or biting them gently about the head;
they seem as if they whispered into their ears
the sweets of love; and then they mount upon
their backs and invite them by other arts to
fruition: among the number may be men-
tioned pigeons and sparrows.
It did not therefore appear likely that a
few treads, in the beginning of the year, should
suffice to render fertile the whole of the eggs
that are to be laid in its course.
Upon one occasion, however, in the spring
season, by way of helping out Fabricius, and
that I might have some certain data as to
the time during which the fecundating influ-
ence of intercourse would continue, and the
necessity of renewed communication, 1 had a
couple of hens separated from the cock for four
days, each of which laid three eggs, all of which
were prolific, Another hen was secluded, and
the egg she laid on the tenth day afterwards
was fruitful. The egg which another laid on
the twentieth day of her seclusion also pro-
duced a chick. It would therefore seem that
intercourse, once or twice repeated, suffices to
impregnate the whole bunch of yelks, the
whole of the eggs that will be laid during a cer-
tain season.
I shall here relate another observation which
I made at this time. When I returned two of
the hens, which I had secluded for a time, to
the cock, one of which was big with egg, the
other having but just laid, the cock immedi-
ately ran to the latter and trod her greedily
three or four times; the former he went round
and round, tripping himself with his wing and
seeming to salute her, and wish her joy of her
return; but he soon returned to the other and
trod her again and again, even compelling her
to submit; the one big with egg, however, he
always speedily forsook, and never solicited
her to his pleasure. I wondered with myself by
what signs he knew that intercourse would ad-
vantage one of these hens and prove unavail-
ing to the other. But indeed it is not easy at
any time to understand how male animals,
even from a distance, know which females are
in season and desirous of their company;
whether it be by sight, or hearing, or smell, it
is difficult to say. Some on merely hearing the
voice of the female, or smelling at the place
where she has made water, or even the ground
35°
WILLIAM HARVEY
over which she has passed, are straightway
seized with desire and set off in pursuit to grat-
ify it. But I shall have more to say on this sub-
ject in my treatise on the Loves, Lusts, and
Sexual Acts of Animals. I return to the matter
we have in hand.
EXERCISE 7. Of the abdomen of the common fowl
and of other birds
From the external orifice proceeding through
the vulva we come to the uterus of the fowl,
in which the egg is perfected, surrounded with
the white and covered with its shell. But be-
fore speaking of the situation and connexions
of this part it seems necessary to premise a few
words on the particular anatomy of the abdo-
men of birds. For I have observed that the
stomach, intestines, and other viscera of the
feathered kinds were otherwise placed in the
abdomen, and differently constituted, than
they are in quadrupeds.
Almost all birds are provided with a double
stomach; one of which is the crop, the other the
stomach, properly so called. In the former the
food is stored and undergoes preparation, in
the latter it is dissolved and converted into
chyme. The familiar names of the two stomachs
of birds are the crop or craw, and the gizzard.
In the crop the entire grain, &c. that is swal-
lowed is moistened, macerated, and softened,
and then it is sent on to the stomach that it may
there be crushed and comminuted. For this end
almost all the feathered tribes swallow sand,
pebbles, and other hard substances, which they
preserve in their stomachs, nothing of the sort
being found in the crop. Now the stomach in
birds consists of two extremely thick and pow-
erful muscles (in the smaller birds they appear
both fleshy and tendinous), so placed that, like
a pair of millstones connected by means of
hinges, they may grind and bruise the food; the
place of teeth, which birds want, being supplied
by the stones which they swallow. In this way
is the food reduced and turned into chyme; and
then by compression (just as we are wont, after
having bruised an herb or a fruit, to squeeze
out the juice or pulp) the softer or more liquid
part is forced out, comes to the top, and is trans-
ferred to the commencement of the intestinal
canal; which in birds takes its rise from the up-
per part of the stomach near the entrance of
the oesophagus. That this is the case in many
genera of birds is obvious; for the stones and
other hard and rough substances which they
have swallowed, if long retained, become so
smooth and polished that they are unfit to com-
minute the food, when they are discharged.
Hence birds, when they select stones, try them
with their tongue, and, unless they find them
rough, reject them. In the stomach of both the
ostrich and cassowary I found pieces of iron and
silver, and stones much worn down and almost
reduced to nothing; and this is the reason why
the vulgar believe that these creatures digest
iron and are nourished by it.
If you apply the body of a hawk or an eagle,
or other bird of prey, whilst fasting, to your
ear, you will hear a distinct noise, occasioned by
the rubbing, one against another, of the stones
contained in the stomach. For hawks do not
swallow pebbles with a view to cool their stom-
achs, as falconers commonly but erroneously
believe, but that the stones may serve for the
comminution of their food; precisely as other
birds, which have muscular stomachs, swallow
pebbles, sand, or something else of the same
nature, to crush and grind the seeds upon which
they live.
The stomach of birds, then, is situated with-
in the cavity of the abdomen, below the heart,
lungs and liver: the crop, however, is without
the body in some sort, being situated at the
lower part of the neck, over the os jugale or
merry- thought. In this bag, as I have said, the
food is only macerated and softened; and sev-
eral birds regurgitate and give it to their young,
in some measure as quadrupeds feed their prog-
eny with milk from their breasts; this occurs in
the whole family of the pigeons, and also among
rooks. Bees, too, when they have returned to
their hives, disgorge the honey which they have
collected from the flowers and concocted in
their stomachs, and store it in their waxen cells;
and so also do hornets and wasps feed their
young. The bitch has likewise been seen to vom-
it the food which she had eaten some time be-
fore, in a half-digested state, and give it to her
whelps: it is not, therefore, to be greatly won-
dered at, if we see the poor women, who beg
from door to door, when their milk fails, feed-
ing their infants with food which they have
chewed and reduced to a pulp in their own
mouths.
The intestines commence in birds, as has been
said, from the upper part of the stomach, and
are folded up and down in the line of the longi-
tudinal direction of the body, not transversely
as in man. Immediately below the heart, about
the waist, and where the diaphragm is situated
in quadrupeds, for birds have no diaphragm,
we find the liver, of ample size, divided into
two lobes situated one on either side (for birds
ANIMAL GENERATION
have no spleen) and filling the hypochondria.
The stomach lies below the liver, and down-
wards from the stomach comes the mass of in-
testines, with numerous delicate membranes,
full of air, interposed; the trachea opening in
birds, as already stated, by several gaping ori-
fices into membranous abdominal cells. The
kidneys, which are of large size in birds, are of
an oblong shape, look as if they were made up
of fleshy vesicles, without cavities, and lie along
the spine on either side, with the descending
aorta and vena cava abdominalis adjacent; they
further extend into and seem to lie buried with-
in ample cavities of the ossa ilia. The ureters
proceed from the anterior aspects of the kid-
neys, and run longitudinally towards the cloaca
and podex, in which they terminate, and into
which they pour the liquid excretion of the kid-
neys. This, however, is not in any great quan-
tity in birds, because they drink little, and
some of them, the eagle for example, not at all.
Nor is the urine discharged separately and by
itself, as in other animals; but, as we have said,
it distils from the ureters into the common
cloaca, which is also the recipient of the faeces,
and the discharge of which it facilitates. The
urine is also different in birds from what it is in
other animals; for, as the urine in the generality
of animals consists of two portions, one more
serous and liquid, another thicker, which, in
healthy subjects constitutes the hypostasis or
sediment, and subsides when the urine becomes
cold; so is it in birds, but the sedimentary por-
tion is the more abundant, and is distinguished
from the liquid by its white or silvery colour:
nor is this sediment met with only in the cloaca
(where it abounds, indeed, and surrounds the
faeces), but in the whole course of the ureters,
which are distinguished from the coverings of
the kidneys by their white colour. Nor is it only
in birds that this abundant thicker renal secre-
tion is seen; it is conspicuous in serpents and
other ovipara, particularly in those whose eggs
are covered with a harder or firmer membrane.
And here, too, is the thicker in larger pro-
portion than the thinner and more serous por-
tion; its consistency being midway between
thick urine and stercoraceous excrement: so
that, in its passage through the ureters, it re-
sembles coagulated or inspissated milk; once
discharged it soon concretes into a friable
mass.
EXERCISE 8. Of the situation and structure of the
remaining farts ofthefowVs uterus
Between the stomach and the liver, over the
spine, and where, in man and other animals the
pancreas is situated; between the trunk of the
porta and the descending cava; at the origin of
the renal and spermatic arteries, and where the
caeliac artery plunges into the mesentery, there,
in the fowl and other birds, do the ovary and
the cluster of yelks present themselves; having
in their front the trunk of the porta, the gullet,
and the orifice of the stomach: behind them,
the vena cava and the aorta descending along
the spine; above the liver, and beneath the
stomach, lie adjacent. The infundibulum, there-
fore, which is a most delicate membrane, de-
scends from the ovary longitudinally with the
spine, between it and the gizzard. And from
the infundibulum (between the gizzard, the
intestines, the kidneys, and the loins), the
processus uteri or superior portion of this organ
descends with a great many turnings and cells
(like the colon and rectum in man), into the
uterus itself. Now the uterus, which is continu-
ous with this process, is situated below the giz-
zard, between the loins, the kidneys, and the
rectum, in the lower part of the abdomen, close
to the cloaca; so that the egg surrounded with
its white, which the uterus contains, is situated
so low that, with the fingers, it is easy to ascer-
tain whether it be soft or hard, and near the
laying.
The uterus in the common fowl varies both
in point of size and of structure. In the fowl
that is with egg, or that has lately laid, it is very
different from what it is in the pullet, the uterus
of which is fleshy and round, like an empty
purse, and its cavity so insignificant that it
would scarcely contain a bean; smooth exter-
nally, it is wrinkled and occupied by a few
longitudinal plicae internally: at first sight you
might very well mistake it either for a large
urinary bladder or for a second smaller stom-
ach. In the gravid state, however, and in the
fowl arrived at maturity (a fact which is indi-
cated by the redder colour of the comb), the
uterus is of much larger dimensions and far
more fleshy; its plicae are also larger and thicker,
it in general approaches the size which we
should judge necessary to receive an egg; it ex-
tends far upwards in the direction of the spinal
column, and consists of numerous divisions or
cells, formed by replications of the extended
uterus, similar to those of the colon in quad-
rupeds and man. The inferior portion of the
uterus, as the largest and thickest, and most
fleshy of all, is strengthened by many plicae of
large size. Its configuration internally is oval, as
if it were the mould of the egg. The ascending
352
WILLIAM HARVEY
or produced portion of the uterus I designate
the processus uteri: this part Fabricius calls the
uterus secundus, and says that it consists of three
spiral turns or flexures; Ulyssus Aldrovandus,
again, names it the stomachum uteri, I must ad-
mit that in this part there are usually three
turns to be observed; they are not, however, by
any means so regular but that, as in the case of
the cells of the colon, nature sometimes departs
from her usual procedure here.
The uterus as it ascends higher, so does it be-
come ever the thinner and more delicate, con-
taining fewer and smaller plicae, until at length
going off into a mere membrane, and that of the
most flimsy description, it constitutes the in-
fundibulum; which, reaching as high as the
waist or cincture of the body, embraces the
entire ovary.
On this account, therefore, Fabricius de-
scribes the uterus as consisting of three por-
tions; viz., the commencement, the middle,
and the end. "The commencement," says he,
"degenerating into a thin and most delicate
membrane, forms an ample orifice, and bears a
resemblance to an open-mouthed tube or fun-
nel. The next portion (which I call the pro-
cessus uteri), consisting of three transverse spi-
ral turns, serves for the supply of the albumen,
and extends downwards to the most inferior
and capacious portion— the termination of the
uterus— in which the chalazae, the two mem-
branes, and the shell are formed."1
The whole substance of the uterus, particu-
larly the parts about the plicae, both in its body
and in its process, are covered with numerous
ramifications of blood-vessels, the majority of
which are arterial rather than venous branches.
The folds which appear oblique and trans-
verse in the interior of the uterus are fleshy
substances; they have a fine white or milky
colour, and a sluggish fluid oozes from them, so
that the whole of the interior of the uterus, as
well the body as the process, is moistened with
an abundance of thin albumen, whereby the
vitellus as it descends is increased, and the albu-
men that is deposited around it is gradually
perfected.
The uterus of the fowl is rarely found other-
wise than containing an egg, either sticking in
the spiral process or arrived in the body of the
organ. If you inflate this process when it is
empty it then presents itself as an oblique and
contorted tube, and rises like a turbinated shell
or cone into a point. The general arrangement
of the spirals and folds composing the uterus, is
1 Op. «/., p. 17.
such as we have already observed it in the vulva:
there is a ready enough passage for the descend-
ing egg, but scarce any return even for air
blown in towards the superior parts.
The processus uteri with its spirals, very small
in the young pullet, is so much diminished in
the hen which has ceased laying, that it shrinks
into the most delicate description of membrane,
and then entirely disappears, so that no trace
of it remains, any more than of the ovary or
infundibulum: nothing but a certain glandular-
looking and spongy mass appears in the place
these bodies occupied, which in a boiled fowl
tastes sweet, and bears some affinity to the pan-
creas and thymus of young mammiferous ani-
mals, which, in the vernacular tongue, are
called the sweetbread.
The uterus and the processus uteri are con-
nected with the back by means of a membra-
nous attachment, which Fabricius designates by
the name of "mesometrium; because the second
uterus, together with this vascular and mem-
branous body, may very fairly be compared
with the intestines and the mesentery." For, as
the intestine is bound down by the mesentery,
so is this portion of the uterus attached to the
spinal column by an oblong membranous proc-
ess; lest by being too loose, and getting twisted,
the passage of the yelks should be interfered with,
instead of having a free and open transit af-
forded them as at present. The mesometrium al-
so transmits numerous blood-vessels, surcharged
with blood, to each of the folds of the uterus.
In its origin, substance, structure, use, and of-
fice, this part is therefore analogous to the mes-
entery. Moreover, from the fundus of the uterus
lengthwise, and extending even to the infun-
dibulum, there is a ligament bearing some re-
semblance to a tape-worm, similar to that which
we notice in the upper part of the colon. It is as
if a certain portion or stripe of the external
tunic had been condensed and shortened in
such a manner that the rest of the process is
thrown into folds and cells: were you to draw a
thread through a piece of intestine taken out
of the body, and to tie this thread firmly on
one side, you would cause the other side
of the bowel to pucker up into wrinkles and
cells.
This then, in brief, is the structure of the
uterus in the fowl that is laying eggs: fleshy,
large, extensible both longitudinally and trans-
versely, tortuous or winding in spirals and con-
volutions from the cloaca upwards, in the line
of the vertebral column, and continued into
the infundibulum.
ANIMAL GENERATION
353
EXERCISE 9. Of the extrusion of the egg, or
parturition of the fowl, in general
The yelk, although only a minute speck in
the ovary, gaining by degrees in depth of colour
and increasing in size, gradually acquires the
dimensions and characters that distinguish it at
last. Cast loose from the cluster, it descends by
the infundibulum, and, transmitted through
the spirals and cells of the processus uteri, it be-
comes surrounded with albumen; and this,
without in any place adhering to the uterus (as
was rightly observed by Fabricius in opposition
to Aristotle), or growing by means of any sys-
tem of umbilical vessels; but as the eggs of fishes
and frogs, when extruded and laid in the water
provide and surround themselves with albu-
men, or as beans, vetches, and other seeds and
grains swell when moistened, and thence sup-
ply nourishment to the germs that spring from
them, so, from the folds of the uterus that have
been described, as from an udder, or uterine
placenta, an albuminous fluid exudes, which
the vitellus, in virtue of its inherent vegetative
heat and faculty, attracts and digests into the
surrounding white. There is, indeed, an abun-
dance of fluid having the taste of albumen, con-
tained in the cavity of the uterus and entangled
between the folds that cover its interior. In this
way does the yelk, descending by degrees, be-
come surrounded with albumen, until at last,
having in the extreme part of the uterus ac-
quired a covering of firmer membranes and a
harder shell, it is perfected and rendered fit for
extrusion.
EXERCISE 10. Of the increase and nutrition of the
CSS
Let us hear Fabricius on these topics. He
says: ''As the action of the stomach is to pre-
pare the chyle, and that of the testes to secrete
the seminal fluid (because in the stomach chyle
is discovered, and in the testes semen), so we
declare the act of the uterus in birds to be the
production of eggs, because eggs are found
there. But this, as it appears, is not the only ac-
tion of uteri; to it must be added the increase
of the egg, which succeeds immediately upon
its production, and which proceeds until it is
perfected and attains its due size. For a fowl
does not naturally lay an egg until it is perfect
and has attained to its proper dimensions. The
office of the uterus is, therefore, the growth as
well as the generation of the egg; but growth
implies and includes the idea of nutrition; and,
as all generation is the act of two principles, one
the agent, another the matter, the agent in the
production of eggs is nothing else than the or-
gans or instruments indicated, viz.* the com-
pound uterus; and the matter nothing but the
blood."
We, studious of brevity, and shunning all
controversy, as in duty bound, as we readily ad-
mit that the office and use of the uterus is the
procreation of the egg, so do we maintain the
"adequate efficient/' as it has been called, the
immediate agent to inhere in the egg itself; and
we assert, further, that the egg is both engen-
dered and made to increase, not by the uterus,
but by a certain natural principle peculiar to
itself; and that this principle flows from the
whole fowl into the rudiments of the vitelius,
and whilst it was yet but a speck, and under the
influence either of the calidum innatum or of
nature, causes it to be nourished and to grow;
just as there is a certain faculty in every par-
ticle of the body which secures its nutrition
and growth.
As regards the manner in which the yelk is
surrounded by the albumen, Aristotle appears
to have believed1 that in the sharp end of the
egg (where he placed the commencement of
the egg), whilst it was yet surrounded by soft
membranes, there existed an umbilical canal, by
which it was nourished; a view which Fabri-
cius2 challenges, denying that there is any such
canal, or that the vitellus has any kind of con-
nexion with the uterus. He further lessens the
doubt in regard to the albumen of the extruded
egg, observing, that "the egg increases in a
twofold manner, inasmuch as the uterus con-
sists of two portions, one superior, another in-
ferior; and the egg itself consists of two mat-
ters— the yelk and the white. The yelk increases
with a true growth, to wit, by means of the
blood, which is sent to it through the veins
whilst it is yet connected with the vitellarium.
The albumen, however, increases and grows
otherwise than the yelk; viz., not by means of
the veins, nor by proper nutrition like the yelk,
but, by juxtaposition, adhering to the vitellus
as it is passing through the second uterus."
But my opinion is that the egg increases
everywhere in the same manner as the yelk
does in the cluster; viz., by an inherent con-
cocting principle; with this single difference,
that in the ovary the nourishment is brought
to it by means of vessels, whilst in the uterus it
finds that which it imbibes already prepared for
it. Juxtaposition of parts is equally necessary in
1 On the Generation of Animals, in. 2.
*Opcit., p. ii.
354
WILLIAM HARVEY
every kind of nutrition and growth, and so also
are concoction and distribution of the applied
nutriment. Nor is one of these to be less ac-
counted true nutrition than the other, inasmuch
as in both there is accession of new aliment, ap-
position, agglutination, and transmutation of
particles. Nor can vetches or beans, when they
attract moisture from the earth through their
skins, imbibing it like sponges, be said with less
propriety to be nourished than if they had ob-
tained the needful moisture through the mouths
of veins; and trees, when they absorb the dew
and the rain through their bark, are as truly
nourished as when they pump them in by their
roots. With reference to the mode in which nu-
trition is effected, we have set down much in
another place. It is another difficulty that occu-
pies us at this time, viz., whether the yelk,
whilst it is acquiring the white, does not make
a certain separation and distinction in it;
whether, in the course of the increase, a more
earthy portion does not subside into the yelk
or middle of the egg as towards the centre,
which Aristotle believed, and another lighter
portion surrounds this. For between the yelk
which is still in the cluster, and the yelk which
is found in the middle of a perfect egg, there is
this principal difference, that although the for-
mer be of a yellow colour, still, in point of con-
sistence, it rather resembles the white; and by
boiling, it is, like the latter, thickened, com-
pacted, inspissated, and becomes divisible into
layers; whilst the yelk of the perfect egg is
rendered friable by boiling, and is rather of an
earthy consistency, not thick and gelatinous
like albumen.
EXERCISE 11. Of the covering or shell of the egg
It will now be proper, having spoken of the
production of eggs, to treat of their parts and
diversities. "An egg," says Fabricius, "con-
sists of a yelk, the albumen, two chalazae, three
membranes, viz., one proper to the vitellus, two
common to the entire egg, and a shell. To these
two others are to be added, which, however,
cannot be correctly reckoned among the parts
of an egg; one of these is a small cavity in the
blunt end of the egg, under the shell; the other
is a very small white spot, a kind of round cica-
tricula connected with the surface of the yelk.
The history of each of these parts and accidents
must now be given more particularly, and we
shall begin from without and proceed inwards.
"The external covering of the egg, called by
Pliny the cortex and putamen, by Quintus
Serenus the testa ovi, is a hard but thin, friable
and porous covering, of different colours in dif-
ferent cases — white, light green, speckled, &c,
All eggs are not furnished with a shell on theii
extrusion: the eggs of serpents have none; and
some fowls occasionally, though rarely, lay
eggs that are without shells. The shell, though
everywhere hard, is not of uniform hardness:
it is hardest towards the upper end." From this
Fabricius1 opines that we are to doubt as to the
matter of which, and the season at which the
shells of eggs are produced. Aristotle2 and Pliny2
affirm that the shell is not formed within the
body of the fowl, but when the egg is laid; and
that as it issues it sets by coming in contact
with the air, the internal heat driving off
moisture. And this, says Aristotle,4 is so ar-
ranged to spare the animal pain, and to render
the process of parturition more easy. An egg
softened in vinegar is said to be easily pushed
into a vessel with a narrow mouth."
Fabricius was long indisposed to this opinion,
"because he had found an egg within the body
of the fowl covered with a hard shell; and
housewives are in the daily practice of trying
the bellies of their hens with their fingers in or-
der that they may know by the hardness
whether the creatures are likely to lay that day
or not." But by and by, when "he had been as-
sured by women worthy of confidence, that the
shells of eggs became hardened in their passage
into the air, which dissipates a certain moisture
diffused over the egg on its exit, fixing it in the
shell not yet completely hardened"; and having
afterwards "confirmed this by his owa experi-
ence," he altered his opinion, and came to the
conclusion, "that the egg surrounded with a
shell, and having a consistency betwixt hard
and soft, hardened notably at the moment of
its extrusion, in consequence, according to
Aristotle's views, of the concretion and dissipa-
tion of the thinner part of a certain viscid and
tenacious humour, bedewed with which the egg
is extruded; sticking to the recent shell this
humour is dried up and hardened, the cold of
the ambient air contributing somewhat to the
effect. Of all this," he says, "you will readily be
satisfied if you have a fowl in the house, and
dexterously catch the egg in your hand as it is
dropping."
I was myself long fettered by this statement
of Aristotle, indeed until certain experience
1 Loc, cit., p. 13.
2 History of Animals^ vi. 2; On the Generation of Ani-
mals, i. 8.
*Hist. nat,, x. 52.
* On the Generation of Animals, in, 2.
ANIMAL GENERATION
355
had assured me of its erroneousness; for I found
the egg still contained in the uterus, almost al-
ways covered with a hard shell; and I once saw
an egg taken from the body of a living fowl,
and still warm, without a shell but covered with
a tenacious moisture; this egg, however, did
not acquire any hardness through the concre-
tion or evaporation of the moisture in ques-
tion, as Fabricius would have us believe, nei-
ther was it in any way changed by the cold of
the surrounding air; but it retained the same
degree of softness which it had had in the
uterus.
I have also seen an egg just laid by a fowl,
surrounded by a complete shell, and this shell
covered externally with a soft and membranous
skin, which however did not become hard. I
have further seen another hen's egg covered
with a shell everywhere except at the extremity
of the sharp end, where a certain small and soft
projection remained, very likely such as was
taken by Aristotle for the remains of an um-
bilicus.
Fabricius, therefore, appears to me to have
wandered from the truth; nor was I ever so
dexterous as to catch an egg in its exit, and dis-
cover it in the state between soft and hard. And
this I confidently assert, that the shell is formed
internally, or in the uterus, and not otherwise
than all the other parts of the egg, viz., by the
peculiar plastic power. A statement which I
make all the more confidently because I have
seen a very small egg covered with a shell, con-
tained within another larger egg, perfect in all
respects, and completely surrounded with a
shell. An egg of this kind Fabricius calls an
ovum centeninum; and our housewives ascribe
it to the cock. This egg I showed to his Serene
Majesty King Charles, my most gracious mas-
ter, in the presence of many persons. And the
same year, in cutting up a large lemon, I found
another perfect but very small lemon included
within it, having a yellow rind like the other;
and I hear that the same thing has frequently
been seen in Italy.
It is a common mistake with those who pur-
sue philosophical studies in these times, to seek
for the cause of diversity of parts in diversity
of the matter whence they arise. Thus medical
men assert that the several parts of the body
are both engendered and nourished by diverse
matters, either the blood or the seminal fluid;
viz., the softer parts, such as the flesh, by the
thinner matter, the harder and more earthy
parts, such as the bones, &c. by the firmer and
thicker matter. But we have elsewhere refuted
this too prevalent error. Nor do they err less
who, with Democritus, compose all things of
atoms; or with Empedocles, of elements. As if
generation were nothing more than a separation,
or aggregation, or disposition of things. It is not
indeed to be denied that when one thing is to
be produced from another, all these are nec-
essary, but generation itself is different from
them all. I find Aristotle to be of this opinion;
and it is my intention, by and by, to teach that
out of the same albumen (which all allow to be
uniform, not composed of diverse parts), all
the parts of the chick, bones, nails, feathers,
flesh, &c. are produced and nourished. More-
over, they who philosophize in this way, assign
a material cause, and deduce the causes of nat-
ural things either from the elements concurring
spontaneously or accidentally, or from atoms
variously arranged; they do not attain to that
which is first in the operations of nature and in
the generation and nutrition of animals; viz.,
they do not recognize that efficient cause and
divinity of nature which works at all times with
consummate art, and providence, and wisdom,
and ever for a certain purpose, and to some good
end; they derogate from the honour of the Di-
vine Architect, who has not^contrived the shell
for the defence of the egg with less of skill and
of foresight than he has composed all the other
parts of the egg of the same matter, and pro-
duced it under the influence of the same form-
ative faculty.
Although what has already been said be the
fact, namely, that the egg, even whilst con-
tained in the uterus, is provided with a hard
shell, still the authority of Aristotle has always
such weight with me that I never think of dif-
fering from him inconsiderately; and I there-
fore believe, and my observations bear me out
in so much, that the shell does gain somewhat
in solidity from the ambient air upon its extru-
sion; that the sluggish and slippery fluid with
which it is moistened when laid, immediately
becomes hardened on its exposure to the air.
For the shell, whilst the egg is in the uterus, is
much thinner and more transparent, and
smoother on the surface; when laid, however,
the shell is thicker, less translucid, and the sur-
face is rough — it appears as if it were powdered
over with a fine white dust which had but just
adhered to it.
Let us, as we are upon this subject, expatiate
a little:
In the desert islands off the east coast of Scot-
land, such flights of almost every kind of sea-
fowl congregate, that were I to state what I
356
WILLIAM HARVEY
have heard from parties very worthy of credit, I
fear I should be held guilty of telling greater
stories than they who have committed them-
selves in regard to the Scottish geese produced,
as they say, from the fruits of certain trees that
had fallen into the sea. These geese the narrators
themselves had never seen so produced; but I
will here relate that which I have myself wit-
nessed.
There is a small island which the Scots call
the Bass Island (and speaking of this one will
suffice for all), situated in the open ocean, not
far from the shore, of the most abrupt and pre-
cipitous character, so that it rather resembles
one huge rock or stone than an island, and in-
deed it is not more than a mile in circumfer-
ence. The surface of this island in the months
of May and June is almost completely covered
with nests, eggs, and young birds, so that you
can scarce find free footing anywhere; and then
such is the density of the flight of the old birds
above, that like a cloud they darken the sun
and the sky; and such the screaming and din
that you can scarce hear the voice of one who
addresses you. If you turn your eyes below, and
from your lofty stance and precipice regard the
sea, there you perceive on all sides around an in-
finite variety of different kinds of sea-fowl
swimming about in pursuit of their prey: the
face of the ocean is very like that of a pool in
the spring season, when it appears swarming
with frogs; or to those sunny hills and cliffy
mountains looked at from below, that are cov-
ered with numerous flocks of sheep and goats.
If you sail round the island and look up, you
see on every ledge and shelf, and recess, in-
numerable flocks of birds of almost every size
and order; more numerous than the stars that
appear in the unclouded moonless sky; and if
you regard the flights that incessantly come
and go you may imagine that it is a mighty
swarm of bees you have before you. I should
scarcely be credited did I name the -revenue
which was annually derived from the feathers,
the eggs, and the old nests, which, as useful for
firing, are all made objects of traffic by the pro-
prietor; the sum he mentioned to me exceeds
credibility. There was this particular feature
which, as it refers to our subject, I shall men-
tion, and also as it bears me out in my report of
the multitudes of sea-fowl: the whole island ap-
pears of a brilliant white colour to those who ap-
proach it-— all the cliffs look as if they consisted
of the whitest chalk; the true colour of the
rock, however, is dusky and black. It is a friable
white crust that is spread over all, which gives
the island its whiteness and splendour, a crust,
having the same consistency, colour, and nature
as an egg-shell, which plasters everything with
a hard, though friable and testaceous kind of
covering. The lower part of the rock, laved by
the ebbing and flowing tide, preserves its native
colour, and clearly shows that the whiteness of
the superior parts is due to the liquid excre-
ments of the birds, which are voided along with
the alvine faeces; which liquid excrements,
white, hard, and brittle like the shell of the egg,
cover the rock, and, under the influence of the
cold of the air, incrust it. Now this is precisely
the way in which Aristotle and Pliny will have
it that the shell of the egg is formed. None of
the birds are permanent occupants of the island,
but visitors for purposes of procreation only,
staying there for a few weeks, in lodgings, as it
were, and until their young ones can take wing
along with them. The white crust is so hard
and solid, and adheres so intimately to the rock,
that it might readily be mistaken for the natu-
ral soil of the place.
The liquid, white, and shining excrement is
conveyed from the kidneys of birds by the ure-
ters, into the common receptacle or cloaca;
where it covers over the alvine faeces, and with
them is discharged. It constitutes, in fact, the
thicker portion of the urine of these creatures,
and corresponds with that which, in our urine,
we call the hypostase or sediment. We have al-
ready said something above on this topic, and
have entered into it still more fully elsewhere.
We always find an abundance of this white ex-
crement in mews; where hawks besmear walls
beside their perches, they cover them with a
kind of gypseous crust, or make them look as
if they were painted with white lead.
In the cloaca of a dead ostrich I found as
much of this gypseous cement as would have
filled the hand. And in like manner the same
substance abounds in tortoises and other ovi-
parous animals; discharged from the body it
soon concretes either into a friable crust, or in-
to a powder which greatly resembles pulverized
egg-shells, in consequence of the evaporation
of its thinner part.
Among the many different kinds of birds
which seek the Bass Island for the sake of laying
and incubating their eggs, and which have such
variety of nests, one bird was pointed out to me
which lays but one egg, and this it places upon
the point of a rock, with nothing like a nest or
bed beneath it, yet so firmly that the mother
can go and return without injury to it; but if
anyone move it from its place, by no art can it
ANIMAL GENERATION
357
be fixed or balanced again; left at liberty, it
straightway rolls off and falls into the sea. The
place, as I have said, is crusted over with a
white cement, and the egg, when laid, is be-
dewed with a thick and viscid moisture, which
setting speedily, the egg is soldered as it were,
or agglutinated to the subjacent rock.
An instance of like rapid concretion may be
seen any day at a statuary's, when he uses his
cement of burnt alabaster or gypsum tempered
with water; by means of which the likeness of
one dead, or the cast of anything else may be
speedily taken, and used as a mould.
There is also in like manner a certain earthy
or solid something in almost all liquids, as, for
example, tartar in wine, mud or sand in water,
salt in lixivium, which, when the greater por-
tion of the water has been dissipated, concretes
and subsides; and so do I conceive the white
sediment of birds to descend along with the
urine from the kidneys into the cloaca, and
there to cover over and mcrust the egg, much
as the pavement of a mews is plastered over by
falcons, and every cliff of the aforementioned
island by the birds that frequent it; much also
as chamber utensils, and places where many per-
sons make water, become covered with a yellow
incrustation; that substance, in fact, concret-
ing externally, of which calculi in the kidneys,
bladder, and other parts are formed. I did
formerly believe then, as I have said, persuaded
especially by the authority of Aristotle and
Pliny, that the shell of the hen's egg was
formed of this white sediment, which abounds
in all the oviparous animals whose eggs are laid
with a hard shell, the matter concreting through
contact with the air when the egg was laid. And
so many additional observations have since
strengthened this conclusion that I can scarcely
keep from believing that some part at least of
the shell is thus produced.
Nevertheless, I would say with Fabricius:
"Let all reasoning be silent when experience
gainsays its conclusions." The too familiar vice
of the present age is to obtrude as manifest
truths, mere fancies, born of conjecture and
superficial reasoning, altogether unsupported
by the testimony of sense.
For I have very certainly discovered that the
egg still contained in the uterus, in these coun-
tries at least, is covered with its shell; although
Aristotle and Pliny assert the contrary, and
Fabricius thinks that "it is not to be too ob-
stinately gainsaid." In warmer places, perhaps,
and where the fowls are stronger, the eggs may
be extruded soft, and for the most part without
shells. With us this very rarely happens. When
I was at Venice in former years, Aromatarius, a
learned physician, showed me a small leaf which
had grown between the two valves of a peascod,
whilst with us there is nothing more apparent
in these pods than a small point where the germ
is about to be produced. So much do a milder
climate, a brighter sky, and a softer air, con-
duce to increase and rapidity of growth.
EXERCISE 12. Of the remaining parts of the egg
We have already spoken partially of the place
where, the time when, and the manner how the
remaining parts of the egg are engendered, and
we shall have something more to add when we
come to speak of their several uses.
"The albumen," says Fabricius, "is the ovi
albus liquor of Pliny, the ovi candidum of Cel-
sus, the ovi albor of Palladius, the ovi album et
albumentum of Apicius, the \tvn6v of the
Greeks, the cbou XeuKWjua of Aristotle, the
6pn0os 7dXa, or bird's milk, of Anaxagoras.
This is the cold, sluggish, white fluid of the
egg, of different thickness at different places
(thinner at the blunt and sharp ends, thicker in
other situations) and also in variable quantity
(for it is more abundant at the blunt end, less so
at the sharp end, and still less so in the other
parts of the egg), covering and surrounding the
yelk on every side."1
In the hen's egg, however, I have observed
that there are not only differences in the albu-
men, but two albumens, each surrounded with
its proper membrane. One of these is thinner,
more liquid, and almost of the same consistence
as that humour which, remaining among the
folds of the uterus, we have called the matter
and nourishment of the albumen; the other is
thicker, more viscid, and rather whiter in its
colour, and in old and stale eggs, and those that
have been sat upon for some days, it is of a yel-
lowish cast. As this second albumen every-
where surrounds the yelk, so is it, in like man-
ner, itself surrounded by the more external
fluid. That these two albumens are distinct ap-
pears from this, that if after having removed
the shell you pierce the two outermost mem-
branes, you will perceive the external albumin-
ous liquid to make its escape, and the mem-
branes to become collapsed and to sink down in
the dish; the internal and thicker albumen,
however, all the while retains its place and glob-
ular figure, inasmuch as it is bounded by its
proper membrane, although this is of such ten-
uity that it entirely escapes detection by the
1 Loc. eft., p. 22.
WILLIAM HARVEY
eye; but if you then prick it, the second albu-
men will forthwith begin to flow out, and the
mass will lose its globular shape; just as the
water contained in a bladder escapes when it is
punctured; in like manner the proper investing
membrane of the vitellus being punctured, the
yellow fluid of which it consists escapes, and
the original globular form is destroyed.
"The vitellus," says Fabricius, "is so called
from the word vita, because the chick lives upon
it; from its colour it is also spoken of as the yel-
low of the egg, having been called by the Greeks
generally, xpvabv, by Hippocrates "x\upbv,
and by Aristotle &\pbv and \cKv06i>; the an-
cients, such as Suidas in Menander, called it
vtorbv, /. e., the chick, because they believed
the chick to be engendered from this part. It is
the smoothest portion of the egg, and is con-
tained within a most delicate membrane, im-
mediately escaping if this be torn, and losing
all figure; it is sustained in the middle of the
egg; and in one egg is of a yellow colour, in an-
other of a tint between white and yellow; it is
quite round, of variable size, according to the
size of the bird that lays the egg, and, accord-
ing to Aristotle, of a deeper yellow in water
birds, of a paler hue in land birds."1 The same
author2 also maintains that "the yellow and the
white of an egg are of opposite natures, not
only in colour but in qualities; for the yellow is
inspissated by cold, which the white is not, but
is rather rendered more liquid; and the white,
on the contrary, is thickened by heat, which
the yellow is not, unless it be burned or over-
done, and it is more hardened and dried by
boiling than by roasting." As in the macrocosm
the earth is placed in the centre, and is sur-
rounded by the water and the air, so is the yelk,
the more earthy part of the egg, surrounded by
two albuminous layers, one thicker, another
thinner. And, indeed, Aristotle says that "if we
put a number of yelks and whites together, and
mix them in a pan, and then boil them with a
slow and gentle fire, the whole of the yelks
will set into a globular mass in the middle,
and appear surrounded by the whites."3 But
many physicians have been of opinion that
the white was the colder portion of the
egg. Of these matters, however, more by and
by.
The chalazae, the treads or treadles (gralh-
dura in Italian) are two in number in each egg,
one in the blunt, another in the sharp end.
1 Op. at., p. 23.
2 History of Animals, vi. 2.
8 Ibid.; On the Generation of Animals, in. i.
The larger portion of them is contained in the
white; but they are most intimately connected
with the yelk, and with its membrane. They
are two long-shaped bodies, firmer than the al-
bumen and whiter; knotty, not without a cer-
tain transparency like hail, whence their name;
each chalaza, in fact, is made up of several hail-
stones, as it seems, connected by means of al-
bumen. One of them is larger than the other,
and this extends from the yelk towards the
blunt end of the egg; the other and smaller
chalaza stretches from the yelk towards the
sharp end of the egg. The larger is made up of
two or three knots or seeming hailstones, at a
trifling distance from one another, and of suc-
cessively smaller size.
The chalazae are found in the eggs of all
birds, and in wind and unprolific as well as in
perfect or prolific eggs, duly disposed in both
their extremities. Whence the supposition among
housewives that the chalazae are the tread or
spermatic fluid of the cock, and that the chick
is generated from them is discovered to be a
vulgar error. But Fabricius himself, although
he denies that they consist of the semen of the
cock, still gives various reasons for maintaining
that "they are the immediate matter which
the cock fecundates, and from which the chick
is produced"; a notion which he seeks to prop
by this feeble statement: "because in a boiled
egg, the chalazae are so contracted on them-
selves that they present the figure of a chick al-
ready formed and hatched." But it is not likely
that several rudiments of a single foetus should
be wanted in one egg, neither has anyone ever
discovered the rudiments of the future chick
save in the blunt end of the egg. Moreover the
chalazae present no sensible difference in eggs
that are fecundated by the intercourse of the
two sexes, from those of eggs that are barren.
Our distinguished author is, therefore, mis-
taken in regard to the use of the chalazae in the
egg, as shall further be made to appear by and
by-
In the eggs of even the smallest birds there is
a slender filament, the rudiments of the chala-
zae, to be discovered; and in those of the ostrich
and cassowary I have found, in either end of
the egg very thick chalazae, of great length, and
very white colour, made up of several globules
gradually diminishing in size.
A small cavity is observed in the inside of an
egg under the shell, at the blunt end; some-
times exactly in the middle, at other times
more to one side, almost exactly corresponding
to the chalaza that lies below it. The figure of
ANIMAL GENERATION
359
this cavity is generally circular, though in the
goose and duck it is not exactly so. It is seen as
a dark spot if you hold an egg opposite a candle
in a dark place, and apply your hand edgeways
over the blunt end. In the egg just laid it is of
small size — about the size of the pupil of the
human eye; but it grows larger daily as the egg
is older, and the air is warmer; it is much in-
creased after the first day of incubation; as if by
the exhalation of some of the more external and
liquid albumen the remainder contracted, and
left a larger cavity; for the cavity in question is
produced between the shell and the membrane
which surrounds the whole of the fluids of the
egg. It is met with in all eggs; I have discovered
it, even in those that are still contained in the
uterus, as soon as they had become invested
with the shell. They who are curious in such
matters say that if this cavity be in the point or
end of the egg it will produce a male, if towards
the side, a female. This much is certain: if the
cavity be small it indicates that the egg is
fresh-laid; if large, that it is stale. But we shall
have occasion anon to say more on this head.
There is a white and very small circle appar-
ent in the investing membrane of the vitellus,
which looks like an in branded cicatrice, which
Fabricius therefore calls cicatricula; but he
makes little of this spot, and looks on it rather
as an accident or blemish than as any essential
part of the egg. The cicatricula in question is
extremely small; not larger than a tiny lentil, or
the pupil of a small bird's eye; white, flat, and
circular. This part is also found in every egg,
and even from its commencement in the vitel-
larium. Fabricius, therefore, is mistaken when
he thinks that this spot is nothing more than
the trace or cicatrice of the severed peduncle,
by which the egg was in the first instance con-
nected with the ovary. For the peduncle, as he
himself admits, is hollow, and as it approaches
the vitellus expands, so as to surround or em-
brace, and inclose the yelk in a kind of pouch:
it is not connected with the yelk in the same
way as the stalks of apples and other fruits are
infixed, and so as to leave any cicatrice when
the yelk is cast loose. And if you sometimes
find two cicatriculae in a large yelk, as Fabricius
states, this might, perhaps, lead to the produc-
tion of a monster and double foetus, (as shall be
afterwards shown), but would be no indication
of the pre-existence of a double peduncle. He is,
however, immensely mistaken when he imag-
ines that the cicatricula serves no purpose; for
it is, in fact, the most important part of the
whole egg, and that for whose sake all the
others exist; it is that, in a word, from which
the chick takes its rise. Parisanus, too, is in
error, when he contends that this is the semen
of the cock.
EXERCISE 13. Of the diversities of eggs
"The word ovum, or egg, is taken in a two-
fold sense, proper and improper. An ovum,
properly so designated, I call that body to
which the definition given by Aristotle1 ap-
plies: An egg, says he, is that from part of
which an animal is engendered, and the re-
mainder of which is food for the animal so pro-
duced. But I hold that body to be improperly
styled an egg which is defined by Aristotle2 in
the same place, to be that from the whole of
which an animal is engendered; such as the eggs
of ants, flies, spiders, some butterflies, and
others of the tribe of extremely small eggs;
which Aristotle almost always fears to commit
himself by calling eggs, but which he rather
styles vermiculi" What precedes is from Fab-
ricius;3 but we, whose purpose it is to treat es-
pecially of the generation of the hen's egg, have
no intention to speak of the differences of all
kinds of eggs; we shall limit ourselves to the
diversities among hen's eggs.
The more recently laid are whiter than the
staler, because by age, and especially by incu-
bation, they become darker; the cavity in the
blunt end of a stale egg is also larger than in a
recent egg; eggs just laid are also somewhat
rough to the feel from a quantity of white pow-
der which covers the shell, but which is soon
rubbed off, when the egg becomes smoother as
well as darker. New-laid eggs, unbroken, if
placed near a fire will sweat, and are much more
palatable than those that have been kept for
some time — they are, indeed, accounted a deli-
cacy by some. Eggs, after two or three days' in-
cubation, are still better flavoured than stale
eggs; revived by the gentle warmth of the hen,
they seem to return to the quality and entire-
ness of the egg just laid. Further, I have boiled
an egg to hardness, after the fourteenth day of
incubation, when the chick had already begun
to get its feathers, when it occupied the middle
of the egg, and nearly the whole of the yelk re-
mained, in order that I might better distinguish
the position of the chick: I found it lying, as it
were, within a mould of the albumen, and the
yelk possessed the same agreeable flavour and
sweetness as that of the new-laid egg, boiled to
1 History of Animals, i. 5.
2 Ibid., 2.
9 Op. «'/., p. 19.
360
WILLIAM HARVEY
the same degree of hardness. The yelk taken
from the ovarium of a live fowl, and eaten im-
mediately, tastes much sweeter raw than boiled.
Eggs also differ from one another in shape;
some are longer and more pointed, others round-
er and blunter. According to Aristotle,1 the
long-shaped and pointed eggs produce females;
the blunt, on the contrary, yield males. Pliny,2
however, maintains the opposite. "The round-
er eggs,'* he says, "produce females, the others
males"; and with him Columella3 agrees: "He
who desires to have the greater number of his
brood cocks, let him select the longest and
sharpest eggs for incubation; and on the con-
trary, when he would have the greater number
females, let him choose the roundest eggs."
The ground of Aristotle's opinion was this: be-
cause the rounder eggs are the hotter, and it is
the property of heat to concentrate and deter-
mine, and that heat can do most which is most
powerful. From the stronger and more perfect
principle, therefore, proceeds the stronger and
more perfect animal. Such is the male com-
pared with the female, especially in the case of
the common fowl. On the contrary, again, the
smaller eggs are reckoned among the imperfect
ones, and the smallest of all are regarded as en-
tirely unproductive. It was on this account too
that Aristotle, to secure the highest quality of
eggs, recommends that the hens be frequently
trodden. Barren and adventitious eggs, he as-
serts, are smaller and less savoury, because they
are humid and imperfect. The differences in-
dicated are to be understood as referring to the
eggs of the same fowl; for when a certain hen
goes on laying eggs of a certain character, they
will all produce either males or females. If you
understand this point otherwise, the guess as to
males or females, from the indications given,
would be extremely uncertain. Because dif-
ferent hens lay eggs that differ much in respect
of size and figure: some habitually lay more
oblong, others, rounder eggs, that do not dif-
fer greatly one from another; and although I
sometimes found diversities in the eggs of the
same fowl, these were still so trifling in amount
that they would have escaped any other than
the practised eye. For as all the eggs of the
same fowl acquire nearly the same figure, in the
same womb or mould in which the shell is de-
posited (much as the excrements are moulded
into scybala in the cells of the colon), it neces-
sarily falls out that they greatly resemble one
1 History of Animals, vi. 2.
* Hist, nat., Book x, chap. 52; Book ix.
8 De re rust., 5; Scaliger, in he.
another; so that I myself, without much ex-
perience * could readily tell which hen in a
small flock had laid a given egg, and they who
have given much attention to the point, of
course succeed much better. But that which we
note every day among huntsmen is far more re-
markable; for the more careful keepers who
have large herds of stags or fallow deer under
their charge, will very certainly tell to which
herd the horns which they find in the woods or
thickets belonged. A stupid and uneducated
shepherd, having the charge of a numerous
flock of sheep, has been known to become so
familiar with the physiognomy of each, that if
any one had strayed from the flock, though he
could not count them, he could still say which
one it was, give the particulars as to where it
had been bought, or whence it had come. The
master of this man, for the sake of trying him,
once selected a particular lamb from among
forty others in the same pen, and desired him
to carry it to the ewe which was its dam, which
he did forthwith. We have known huntsmen
who, having only once seen a particular stag, or
his horns, or even his print in the mud (as a lion
is known by his claws), have afterwards been
able to distinguish him by the same marks from
every other; some, too, from the foot-prints of
deer, seen for the first time, will draw inferences
as to the size, and grease, and power of the stag
which has left them; saying whether he were
full of strength, or weary from having been
hunted; and further, whether the prints are
those of a buck or a doe. I shall say thus much
more: there are some who, in hunting, when
there are some forty hounds upon the trace of
the game, and all are giving tongue together,
will nevertheless, and from a distance, tell
which dog is at the head of the pack, which at
the tail, which chases on the hot scent, which is
running off at fault; whether the game is still
running, or is at bay; whether the stag have run
far, or have but just been raised from his lair.
And all this amid the din of dogs, and men, and
horns, and surrounded by an unknown and
gloomy wood. We should not, therefore, be
greatly surprised when we see those who have
experience telling by what hen each particular
egg in a number has been laid. I wish there
were some equally ready way from the child of
knowing the true father.
The principal difference between eggs, how-
ever, is their fecundity or barrenness — the dis-
tinction of fruitful eggs from hypenemic, ad-
ventitious, or wind eggs. Those eggs are called
hypenemic (as if the progeny of the wind) that
ANIMAL GENERATION
361
are produced without the concourse of the
male, and are unfit for setting; although Varro1
declares that the mares, in Lusitania, conceive
by the wind. For zephyrus was held a fertilizing
wind, whence its name, as if it were fcorj^epos,
or life- bringing. So that Virgil says:
And Zephyrus, with warming breath resolves
The bosom of the ground, and melting rains
Are poured o'er all, and every field brings
forth.
Hence the ancients, when with this wind blow-
ing in the spring season, they saw their hens be-
gin laying, without the concurrence of the cock,
conceived that zephyrus, or the west wind, was
the author of their fecundity. There are also
what are called addle, and dog-day eggs, pro-
duced by interrupted incubation, and so called
because eggs often rot in the dog-days, being
deserted by the hens in consequence of the ex-
cessive heat; and also because at this season of
the year thunder is frequent; and Aristotle2 as-
serts that eggs die if it thunders whilst the hen
is sitting.
Those eggs are regarded as prolific, which, no
unfavorable circumstances intervening, under
the influence of a gentle heat, produce chicks.
And this they will do, not merely through the
incubation of the mother, but of any other
bird, if it be but of sufficient size to cherish
and cover them, or by a gentle temperature ob-
tained in any way whatever. "Eggs are hatched
with the same celerity," says Aristotle, "spon-
taneously in the ground, as by incubation.
Wherefore in Egypt, it is the custom to bury
them in dung, covered with earth. And there
was a tale in Syracuse, of a drunken fellow, who
was accustomed to continue his potations un-
til a number of eggs, placed under a mat be-
strewed with earth, were hatched."3 The em-
press Livia, is also said to have carried an egg in
her bosom until a chick was produced from it.
And in Egypt, and other countries, at the pres-
ent time, chickens are reared from eggs placed
in ovens. "The egg, therefore," as Fabricius
truly says, "is not only the uterus, and place
where the generation of the chick proceeds,
but it is that upon which its whole formation
depends; and this the egg accomplishes as
agent, as matter, as instrument, as place, and as
all else that concurs."4
For it is certain that the chick is formed by a
1 DC re rust., u. i.
2 History of Animals, vi. 2; Pliny, Hist, nat., x. 54.
8 Ibid.
4 Op. cit., p. 19.
principle inherent in the egg, and that nothing
accrues to a perfect egg from incubation, be-
yond the warmth and protection; in the same
way as to the chick when disclosed, the hen
gives nothing more than her warmth and her
care, by which she defends it from the cold and
from injury, and directs it to its proper food.
The grand desideratum, therefore, once the
chickens are hatched, is that the hen lead them
about, seek for and supply them with proper
food, and cherish them under her wings. And
this you will not easily supply by any kind of
artifice.
Capons, and hybrids between the common
fowl and the pheasant, produced in our aviaries,
will incubate and hatch a set of eggs; but they
never know how to take care of the brood — to
lead them about properly, and to provide with
adequate care for their nurture.
And here I would pause for a moment (for I
mean to treat of the matter more fully by and
by) to express my admiration of the persever-
ance and patience with which the females of al-
most every species of bird sit upon the nest for
so many days and nights incessantly, macerat-
ing their bodies, and almost destroying them-
selves from want of food; what dangers they
will face in defence of their eggs, and when
compelled to quit them for ever so short a
time, through necessity, with what eagerness
and haste they return to them again, and brood
over them! Ducks and geese, when they quit
the nest for a few minutes, cover and conceal it
with straw. With what true magnanimity do
these ill-furnished mothers defend their eggs!
which, after all, perhaps, are mere wind or
addle eggs, or not their own, or artificial eggs of
chalk or ivory— it is still the same, they defend
all with equal courage. It is truly a remarkable
love which birds display for inert and lifeless
eggs; and their solicitude is repaid by no kind of
advantage or enjoyment. Who does not won-
der at the affection, or passion rather, of the
clucking hen, which can only be extinguished by
a drenching with cold water. In this state of her
feeling she neglects everything, her wings droop,
her feathers are unpruned and ruffled, she wan-
ders about restless and dissatisfied, disturbing
other hens on their nests, seeking eggs every-
where, which she commences forthwith to in-
cubate; nor will she be at peace until her desire
has been gratified, until she has a brood to lead
about with her, upon which she may expend
her fervour, which she may cherish, feed, and
defend. How pleasantly are we moved to laugh-
ter when we see the poor hen following to the
WILLIAM HARVEY
water the supposititious brood of ducklings she
has hatched, wandering restlessly round the pool,
attempting to wade after them to her own immi-
nent peril, and by her noises and various artifices
striving to entice them back to the shore!
According to Aristotle,1 barren eggs do not
produce chicks because their fluids do not
thicken under incubation, nor is the yelk or the
white altered from its original constitution.
But we shall revert to this subject in our gen-
eral survey of generation.
Our housewives, that they may distinguish
the eggs that are addled from those that will
produce chicks, take them from the fourteenth
to the sixteenth day of the incubation, and
drop them softly into tepid water, when the
spoilt ones sink, whilst the fruitful ones swim. If
the included chick be well forward, and moves
about with alacrity, the egg not only rolls over
but even dances in the water. And if you apply
the egg to your ear for several days before the
hatching, you may hear the chick within kick-
ing, scratching, and even chirping. When the
hen that is sitting hears these noises, she turns
the eggs and lays them otherwise than they
were, until the chicks, getting into a comfort-
able position, become quiet; even as watchful
mothers are wont to treat their infants when
they are restless and cry in their cradles.
Hens lay eggs in variable numbers: "Some
hens/' says the philosopher, * 'except the two
winter months, lay through the whole year;
some of the better breeds will lay as many as
sixty eggs before they show a disposition to sit;
though these eggs are not so prolific as those of
the commoner kinds. The Adrianic hens are
small, and lay every day, but they are ill-tem-
pered, and often kill their young ones; they are
particoloured in their plumage. Some domestic
fowls will even lay twice a day; and some, by
reason of their great fecundity, die young."2
In England some of the hens lay every day;
but the more prolific commonly lay two days
continuously and then miss a day: the first day
the egg is laid in the morning, next day in the
afternoon, and the third day there is a pause.
Some hens have a habit of breaking their eggs
and deserting their nests; whether this be from
disease or vice is not known.
Certain differences may also be observed in
the incubation: some fowls only sit once, others
twice, or thrice, or repeatedly. Florentius says
that in Alexandria, in Egypt, there are fowls
called mono sires > from which the fighting cocks
1 History of Animals, vi. 2.
vi. I
are descended, which go on sitting for two or
three periods, each successive brood being re-
moved as it is hatched, and brought up apart.
In this way the same hen will hatch forty, sixty,
and even a greater number of chickens, at a
single sitting.
Some eggs too, are larger, others smaller; a
few extremely small; these, in Italy, are com-
monly called centenina; and our country folks
still believe that such eggs are laid by the cock,
and that were they set they would produce
basilisks. "The vulgar," says Fabricius, "think
that this small egg is the last that will be laid,
and that it comes as the hundredth in number,
whence the name; that it has no yelk, though
all the other parts are present— the chalazae, the
albumen, the membranes, and the shell. And it
seems probable that it is produced when all the
other yelks have been fashioned into eggs, and
no more remain in the vitellary; on the other
hand, however, a modicum of albumen remains,
and out of this, it may be inferred, is the small
egg in question produced/'3 To me, neverthe-
less, this does not appear likely; because it is
certain that the whole ovary being removed,
the uterus secundus also diminishes in size in
the same proportion, and shrinks into a mere
membrane, which contains neither any fluid
nor any albumen. Fabricius proceeds: "The ova
centenina are met with of two kinds: one of
them being without a yelk, and this is the true
centenine egg, because it is the last which the
hen will lay at that particular season— she will
now cease from laying for a time. The other is
also a small egg, but it has a yelk, and will not
prove the last which the hen will then lay, but
is intermediate between those of the usual size
that have preceded, and others that will follow.
It is of small size because there has been a failure
of the vegetative function, as happens to the
peach, and other fruit, of which we see many of
adequate size, but a few that are very diminu-
tive." This may be in consequence of the in-
clemency of the weather, or the want of sun, or
from defective nutriment in point either of
quantity or quality. I should not readily allow,
however, that the eggs last laid are always small.
Monstrous eggs arc not wanting; "for the
augurs," says Aristotle, "held it portentous
when eggs were laid that were all yellow; or
when, on a fowl being laid open, eggs were
found under the septum transversum, where
the rudimentary eggs of the female usually ap-
pear, of the magnitude of perfect eggs."4
1 Op. tit., p. 10.
4 Aldrovandus, Ornithologica, xiv, p. 260.
ANIMAL GENERATION
363
To this head may be referred those eggs that
produce twins, that have two yelks. Such an
egg I lately found in the uterus of a fowl, per-
fect in all respects, and covered with a shell;
the yelks, cicatriculae, and thicker albuminous
portions being all double, and the chalazae pres-
ent in two pairs: a single thinner albumen, how-
ever, surrounded all these, and this in its turn
was included within the usual double common
membrane, and single shell. For, indeed, al-
though Aristotle says that fowls always lay
some eggs of this kind, I shall hardly be induced
to believe that this does not occur against the
ordinary course of nature. And although twin
chicks are produced from such eggs as I have as-
certained in opposition to the opinion of Fab-
ncius, who says that they produce chicks hav-
ing four legs, or four wings and two heads,
which, however, are not capable of living, but
for the most part speedily die, either by reason
of want of room or of air in the shell, or because
the one proves a hinderance to the other and
blights it; nor can it happen that both should be
equally prepared for exclusion — that one should
not prove an abortion.
Briefly and summarily the differences among
eggs are principally of three kinds: some are
prolific, some unprohftc; some will produce
males and some females; some are the produce
of the two sexes of the same species, others of
allied species and will produce hybrids, such as
we see between the common hen and the pheas-
ant, the progeny being referrible either to the
first or to the last male that had connexion
with the hen. Because, according to Aristotle,
"the egg, which receives its constitution by in-
tercourse, passes from its own into another
genus, if the hen be trodden when she carries
either an adventitious egg or one that was con-
ceived under the influence of another male, and
this renewed intercourse take place before the
yellow is changed into the white. So that hy-
penemic or wind eggs are made fruitful, and
fruitful eggs receive the form of the male which
has connexion last. But if the change has taken
place into the white, it cannot happen either
that the wind egg is turned into a fertile one, or
that the egg which is contained in the uterus in
virtue of a previous intercourse, shall be altered
into the genus of the male which has the second
communication."1 For the seminal fluid of the
cock, as Scaliger wittily remarks, is like a testa-
ment, the last will or disposition in which is that
which stands in force.
To these particulars it might perhaps be add-
1 History of Animals, vi. 21.
ed, that some eggs are more strong and lusty
than others, more full of life, if the expression
may be used; though as there is a vital principle
in the egg, so must there inhere the correspond-
ing virtue that flows from it. For, as in other
kinds of animals, some of the females are so re-
plete with desire, so full of Venus, that they
conceive from any and every intercourse, even
once submitted to, and from a weakly male,
and produce several young from the same em-
brace; others, on the contrary, are so torpid and
sluggish, that unless they are assailed by a vig-
orous male, under the influence of strong desire,
and that not once, but repeatedly, and for
a certain time, they continue barren. This is
also the case with eggs, some of which, though
they may have been conceived in consequence
of intercourse, still remain unprolific unless per-
fected by repeated and continued connexions.
Whence it happens that some eggs are more
speedily changed by incubation than others,
exhibiting traces of the foetus from the third
day; others again, either become spoiled, or suf-
fer transformation into the foetus more slowly,
exhibiting no indications of the future chick
even up to the seventh day, as shall be made to
appear by and by, in speaking of the genera-
tion of the chick from the egg.
Thus far have we discoursed of the uterus of
the fowl, and its function; of the production of
the hen's egg, and of its differences and peculi-
arities, from immediate observation; and from
the instances quoted, conclusions may be drawn
with reference to other oviparous animals.
We have now to pursue the history of the
generation and formation of the fcetus from the
egg. For indeed, as I have said above, the en-
tire contemplation of the family of birds is
comprehended in these two propositions: how
is an egg engendered of a male and female; and
by what process do males and females proceed
from eggs? — the circle by which, under favour
of nature, their kinds are continued to eternity.
EXERCISE 14. Of the production of the chic\from
the egg of the hen
Of the growth and generation of the hen's
egg enough has already been said; and we have
now to lay before the reader our observations
on the procreation of the chick from the egg — a
duty which is equally difficult, and profitable,
and pleasant. For in general the first processes
of nature lie hid, as it were, in the depths of
night, and by reason of their subtlety escape
the keenest reason no less than the most pierc-
ing eye.
364
WILLIAM HARVEY
Nor in truth is it a much less arduous busi-
ness to investigate the intimate mysteries and
obscure beginnings of generation than to seek
to discover the frame of the world at large, and
the manner of its creation. The eternity of
things is connected with the reciprocal inter-
change of generation and decay; and as the sun,
now in the east and then in the west, completes
the measure of time by his ceaseless revolu-
tions, so are the fleeting things of mortal exis-
tence made eternal through incessant change,
and kinds and species are perpetuated though
individuals die.
The writers who have treated of this subject
have almost all taken different paths; but hav-
ing their minds preoccupied, they have hither-
to gone to work to frame conclusions in con-
sonance with the particular views they had
adopted.
Aristotle,1 among the ancients, and
Hieronymus Fabricius of Aquapendente,
among the moderns, have written with so much
accuracy on the generation and formation of
the chick from the egg that little seems left for
others to do. Ulyssus Aldrovandus,2 neverthe-
less, described the formation of the chick in ovo;
but he appears rather to have gone by the
guidance of Aristotle than to have relied on his
own experience. For Volcherus Goiter, living
at this time in Bologna, and encouraged, as he
tells us, by Aldrovandus, his master, opened in-
cubated eggs every day, and illustrated many
points besides those noted by Aldrovandus;3
these discoveries, however, could scarcely have
remained unknown to Aldrovandus. i^milius
Parisanus, a Venetian physician, having dis-
carded the opinions of others, has also given a
new account of the formation of the chick from
the egg.
But since our observations lead us to con-
clude that many things of great consequence
are very different from what they have hither-
to been held to be, I shall myself give an ac-
count of what goes on in the egg from day to
day, and what parts are there transmuted, di-
recting my attention to the first days espe-
cially, when all is most obscure and confused,
and difficult of observation, and in reference to
which writers have more particularly drawn
the sword against one another in defence of
their several discordant observations, which, in
sooth, they accommodate rather to their pre-
conceived opinions respecting the material and
1 History of Animals, vi. 2, 3.
J OrntthoL, xiv.
8 Nobtl, excrcit.) vi.
efficient cause of animal generation than to
simple truth.
What Aristotle says on the subject of the re-
production of the chick in ovo is perfectly cor-
rect. Nevertheless, as if he had not himself seen
the things he describes, but received them at
second hand from another expert observer, he
does not give the periods rightly; and then he is
grievously mistaken in respect of the place in
which the first rudiments of the egg are fash-
ioned, stating this to be the sharp end, for
which he is fairly challenged by Fabricius. Nei-
ther does he appear to have observed the com-
mencement of the chick in the egg; nor could
he have found the things which he says are nec-
essary to all generation in the place which he
assigns them. He will, for instance, have it that
the white is the constituent matter (since noth-
ing naturally can by possibility be produced
from nothing). And he did not sufficiently un-
derstand how the efficient cause (the seminal
fluid of the cock) acted without contact; nor
how the egg could, of its own accord, without
any inherent generative matter of the male,
produce a chick.
Aldrovandus, adopting an error akin to that
of Aristotle, says besides, that the yelk rises dur-
ing the first days of the incubation into the
sharp end of the egg, a proposition which no
eyes but those of the blind would assent to; he
thinks also that the chalazae are the semen of
the cock, and that the chick arises from them,
though it is nourished both by the yelk and the
white. In this he is obviously in opposition to
Aristotle, who held that the chalazae con-
tributed nothing to the reproductive powers
of the egg.
Volcherus Goiter is, on the whole, much
more correct; and his statements are far more
consonant with what the eye perceives. But his
tale of the three globules is a fable. Neither did
he rightly perceive the true commencement of
the chick in ovo.
Hieronymus Fabricius contends that the
chalazae are not the sperma of the cock; but
then he will have it that "from these, fecundat-
ed by the seminal fluid of the cock, as from the
appropriate matter, the chick is incorporated."
Fabricius observed the point of origin of the
chick, the spot or cicatricula, namely, which
presents itself upon the tunica propria of the
Slk; but he regarded it as a cicatrice or scar
t on the place where the peduncle had been
attached; he viewed it as a blemish in the egg,
not as any important part.
Parisanus completely refutes Fabricius'
ANIMAL GENERATION
365
ideas of the chalazae; but he himself obviously
raves when he speaks of certain circles, and
principal parts of the foetus, viz., the liver and
heart. He appears to have observed the com-
mencement of the foetus in ovo; but what it was
he obviously did not know, when he says,
"that the white point in the middle of the cir-
cles is the semen of the cock, from which the
chick is produced."
Thus it comes to pass that everyone, in ad-
ducing reasons for the formation of the chick
in QUO, in accordance with preconceived opin-
ions, has wandered from the truth. Some will
have it that the semen or the blood is the mat-
ter whence the chick is engendered; others,
that the semen is the agent or efficient cause of
its formation. Yet to him who dispassionately
views the question is it quite certain that there
is no prepared matter present, nor any menstru-
ous blood to be coagulated at the time of inter-
course by the semen masculinum, as Aristotle
will have it; neither does the chick originate in
the egg from the seed of the male, nor from that
of the female, nor from the two commingled.
EXERCISE 15. The fast examination of the egg;
or of the effect of the fast day's incubation upon
the egg
That we may be the more clearly informed
of the effect which the first day's incubation
produces upon the egg, we must set out by as-
certaining what changes take place in an egg
spontaneously, changes that distinguish a stale
egg from one that is new-laid, when what is due
to the incubation per se will first be clearly
apprehended.
The space or cavity in the blunt end is pres-
ent, as we have said, in every egg; but the
staler the egg the larger does this hollow con-
tinually grow; and this is more especially the
case when eggs are kept in a warm place, or
when the weather is hot; the effect being due
to the exhalation of a certain portion of the
thinner albumen, as has been stated in the his-
tory of the egg. This cavity, as it increases, ex-
tends rather in the line of the length than of
the breadth of the egg, and comes finally to be
no longer orbicular.
The shell, already less transparent, becomes
dingy.
The albumen grows thicker and more viscid,
and acquires a straw or yellow colour.
The tunica propria of the vitellus becomes
more lax, and appears wrinkled, for it seems
that some even of this fluid is dissipated in the
course of time.
The chalazae are found in either end of every
egg, in the same situation, and having the same
consistence — whether the egg be recentor stale,
fruitful or barren, it does not signify; by their
means a firm connexion is established between
the yelk and the white, and the two fluids pre-
serve their relative positions. The chalazae, in-
deed, are two mutually opposed supports or
poles, and hinges of this microcosm; and are
constructed as if made up of numerous coats of
the albumen, twisted togetherat eitherend into
a knotted rope, by which they are attached to
the vitellus. And hence it happens that the
yelk is separated from the white with difficulty,
unless the chalazae are either first divided with
a knife or torn with the fingers; this done, the
white immediately falls away from the yelk. It
is by means of these hinges that the vitellus is
both retained in the centre of the egg and pre-
served of its proper consistence. And they are
so connected that the principal part, the cicatri-
cula, to wit, always regards the same region of
the egg, or its upper part, and is preserved equi-
distant from either end. For this spot or cica-
tricula is observed to be of the same consistence,
dimensions, and colour, and in the same situa-
tion in the stale as in the new-laid egg. But as
soon as the egg, under the influence of the gen-
tle warmth of the incubating hen, or of warmth
derived from another source, begins topullulate,
this spot forthwith dilates, and expands like the
pupil of the eye, and from thence, as the grand
centre of the egg, the latent plastic force breaks
forth and germinates. This first commence-
ment of the chick, however, so far as I am
aware, has not yet been observed by any one.
On the second day of the incubation, after
the egg has been exposed to warmth for twen-
ty-four hours, under the hen, as the cavity in
the blunt end has enlarged greatly and de-
scended, so has the internal constitution of the
egg also begun to be changed. The yelk, which
had hitherto lain in the middle of the albumen,
rises towards the blunt end, and its middle,
where the cicatricula is situated, is lifted up
and applied to the membrane that bounds the
empty space, so that the yelk now appears to
be connected with the cavity by means of the
cicatricula; and in the same measure as the yelk
rises does the thicker portion of the albumen
sink into the sharp or lower end of the egg.
Whence it appears, as Fabricius rightly re-
marks, that Aristotle1 was either in error, or
that there is a mistake in the codex, when it is
said, "In this time" (viz., between three and
1 History of Animals, vi. 3.
366
WILLIAM HARVEY
four days, and as many nights), "the yelk is
brought to the summit, where the commence-
ment of the egg is, and the egg is exposed in this
part," /'. e.j under the enlarged empty space.
Now Aristotle1 calls the principium ovi, or
commencement of the egg, its smaller end,
which is last extruded. But it is certain that the
yelk ascends towards the blunt end of the egg,
and that the cavity there enlarges. And Aldro-
vandus is undoubtedly in error when he speaks
as if he had experience of the fact, and says that
the yelk rises to the sharp end. I will confess,
nevertheless, that on the second or third day I
have occasionally observed the cicatncula ex-
panded and the beginning of the chick already
laid, the yelk not having yet risen; this, how-
ever, happens rarely, and I am inclined to as-
cribe it to some weakness in the egg.
On the second day of the incubation, or first
day of inspection, the cicatricula in question is
found to have enlarged to the dimensions
of a pea or lentil, and is divided into circles,
such as might be drawn with a pair of com-
passes, having an extremely minute point for
their centre. It is very probable that Aldrovan-
dus observed this spot, for he says: "In the
midst of the yellow a certain whitish something
makes its appearance, which was not noticed by
Aristotle"; and also by Goiter, when he ex-
presses himself thus: "On the second day there
is in the middle of the yelk a part whiter than
the rest"; Parisanus, too, may have seen it; he
observes: "In the course of the second day I ob-
serve a white body of the size and form of a
middling lentil; and this is the semen of the
cock covered over with a white and most deli-
cate tunic, which underlies the two common
membranes of the entire egg, but overlies the
tunica propria of the yelk." I believe, however,
that no one has yet said that this cicatricula
occurs in every egg, or has acknowledged it to
be the origin of the chick.
Meantime the chalazaeor treadles will be seen
to decline from either end of the egg towards
its sides, this being occasioned by that altera-
tion which we have noticed in the relative sit-
uations of the two fluids. The treadle from the
blunt end descends somewhat; the one from the
sharp end rises in the same proportion: as in a
globe whose axis is set obliquely, one pole is as
much depressed below the horizon as the other
is raised above it.
The vitellus, too, particularly in the situa-
tion of the cicatricula, begins to grow a little
more diffluent than it was, and raises its tunica
1 lbid.% in. 2.
propria (which we have found in stale eggs
before incubation to be somewhat lax and
wrinkled) into a tumour; and it now appears
to have recovered the same colour, consist-
ency, and sweetness of taste that it had in the
egg just laid.
Such is the process in the course of the first
day that leads to the production of a new be-
ing, such the earliest trace of the future chick.
Aldrovandus adds: "the albumen suffers no
change," which is correct; but when he asserts
that "the semen of the cock can be seen in it,"
he as manifestly errs. Resting on a most insuf-
ficient reason, he thought that the chalazae
were the semen of the cock, "because," for-
sooth, "the eggs that are without chalazae are
unfruitful." This I can very well believe; for
these were then no proper eggs; for all eggs,
wind eggs as well as those that are prolific, have
chalazae. But he, misled perhaps by the coun-
try women, who in Italian call the chalazae
galladura, fell into the vulgar error. Nor is Hier-
onymus Fabncius guilty of a less grave mistake
when he exhibits the formation of the chick in
a series of engravings, and contends that it is
produced from the chalazae; overlooking the
fact that the chalazae are present the whole of
the time, and unchanged, though they have
shifted their places; and that the commence-
ment of the chick is to be sought for at a
distance from them.
EXERCISE 16. Second inspection of the egg
The second day gone by, the circles of the
cicatricula that have been mentioned, have be-
come larger and more conspicuous, and may
now be of the size of the nail of the ring-finger,
sometimes even of that of the middle finger. By
these rings the whole cicatricula is indistinctly
divided into two, occasionally into three re-
gions, which are frequently of different colours,
and bear a strong resemblance to the cornea of
the eye, both as respects dimensions, a certain
degree of prominence, and the presence of a
transparent and limpid fluid included within it.
The centre of the cicatricula here stands for
the pupil; but it is occupied with a certain
white speck, and appears like the pupil of some
small bird's eye obscured by a suffusion or cat-
aract, as it is called. On this account we have
called the entire object the oculum ovi, the eye
of the egg.
Within the circles of the cicatricula, I say,
there is contained a quantity of perfectly bright
and transparent fluid, even purer than any crys-
talline humour; which, if it be viewed trans-
ANIMAL GENERATION
367
vcrsely and against the light, the whole spot
will rather appear to be situated in the albumen
than sunk into the membrane of the yelk, as
before: it presents itself as a portion of the al-
bumen dissolved and clarified, and included
within a most delicate tunica propria. Hence I
entitle this fluid the oculum seu colliquamentum
album; it is as if a portion of the albumen, lique-
fied by the heat, shone apart (which it does,
unless disturbed by being shaken) and formed
a more spirituous and better digested fluid, sep-
arated from the rest of the albumen by a tunica
propria, and situated between the two masses of
liquid, the yelk and the albumen. It differs
from the rest of the albumen by its clearness
and transparency, as the water of a pellucid
spring differs from that of a stagnant pool. The
tunic which surrounds this fluid is so fragile and
delicate that, unless the egg be handled with
great care, it is apt to give way, when the pure
spring is rendered turbid by a mixture of fluids.
I was long in doubt what I should conclude as
to this clear diffluent fluid, whether I should re-
gard it as the innate heat, or radical moisture;
as a matter prepared for the future foetus, or a
perfectly-concocted nourishment, such as dew
is held to be among the secondary humours.
For it is certain, as shall be afterwards shown,
that the earliest rudiments of the foetus are cast
in its middle, that from this the chick derives
its first nutriment, and even when of larger size
continues to live amidst it.
This solution, therefore, increases rapidly in
quantity, particularly in its internal region,
which, as it expands, forces out and obliterates
the external regions. This change is effected in
the course of a single day, as is shown in the
second figure of Fabricius. It is very much as it
is with the eyes of those animals which have a
very ample pupil, and see better by night than
by day, such as owls, cats, and others, whose
pupils expand very much in the dusk and dark,
and, on the contrary, contract excessively in a
brilliant light: one of these animals being taken
quickly from a light into a shady place, the pu-
pil is seen to enlarge in such wise that the col-
oured ring, called the iris, is very much dimin-
ished in size, and indeed almost entirely dis-
appears.
Parisanus, falling upon these regions, is gross-
ly mistaken when he speaks of "a honey-col-
oured, a white, a gray, and another white cir-
cle"; and says that "the foetus is formed from
the white middle point" (which, indeed, ap-
pears in these regions), and that "this is the se-
men of the cock." That he may exalt himself on
a more notable subtlety he continues: "Before
any redness is apparent in the body of the foe-
tus, two minute vesicles present themselves in
it; in the beginning, however, neither of them
is tinged with red"; one of these he would have
us receive as the heart, the other as the liver.
But in truth there is neither any vesicle pres-
ent sooner than the redness of the blood is dis-
closed; nor does the embryo ever suddenly be-
come red in the course of the first days of its
existence; nor yet does any of these vesicles
present us with a trace of the liver. Both of
them belong, in fact, to the heart, prefiguring
its ventricles and auricles, and palpitating, as
we shall afterwards show, they respond recip-
rocally by their systoles and diastoles.
Aristotle appears to have known this dis-
solved fluid, when he says: "A membrane, too,
marked with sanguineous fibres, surrounds the
white fluid at this time (the third day), arising
from those orifices of the veins."1 Now the
philosopher can neither be supposed by the
words "white fluid," to refer to the albumen at
large, because at this period the membrane of
the white is not yet covered with veins; it is
only the membrane of the dissolved fluid which
appears with a few branches of veins distributed
over it here and there. And because he says:
"this membrane, too," as if he understood an-
other than those which he had spoken of as in-
vesting the albumen and the yelk before incu-
bation, and designated this one as first arising
after the third day, and from the orifices of the
veins.
Goiter seems also to have known of this dis-
solved fluid; he says: "A certain portion of the
albumen acquiring a white colour, another be-
coming thicker." The fluid in question is sur-
rounded with its proper membrane, and is dis-
tinct and separate from the rest of the albumen
before there is any appearance of blood. We
shall have occasion, by and by, to speak of the
singular importance of this fluid to the foetuses
of every animal. Whilst they float in it they are
safe from succussion and contusion, and other
external injury of every kind; and they, more-
over, are nourished by it. I once showed to their
Serene Majesties the King and Queen, an em-
bryo, the size of a French-bean, which had been
taken from the uterus of a doe; all its mem-
branes were entire, and from its genital organs
we could readily tell that it was a male. It was,
in truth, a most agreeable natural spectacle;
the embryo perfect and elegant, floating in this
pure, transparent, and crystalline fluid, in-
1 History of Animals , vi. 3.
368
WILLIAM HARVEY
vested with its pellucid tunica propria, as if in a
glass vessel of the greatest purity, of the size of
a pigeon's egg.
EXERCISE 17. The third inspection of the egg
Having seen the second process or prepara-
tion of the egg, towards the production of the
embryo which presents itself in the course of
the third day, we proceed to the third stage,
which falls to be considered after the lapse of
three days and as many nights. Aristotle says:
"Traces of generation commence in the egg
of the hen after three days and three nights";1
for example, on Monday morning, if in the
morning of the preceding Friday the egg has
been put under the hen. This stage forms the
subject of the third figure in Fabricius.
If the inspection of the egg be made on the
fourth day, the metamorphosis is still greater,
and the change likewise more wonderful and
manifest with every hour in the course of the
day. It is in this interval that the transition is
made in the egg from the life of the plant to
the life of the animal. For now the margin of
the diffluent fluid looks red, and is purpures-
cent with a sanguineous line, and nearly in its
centre there appears a leaping point, of the
colour of blood, so small that at one moment,
when it contracts, it almost entirely escapes the
eye, and again, when it dilates, it shows like the
smallest spark of fire. Such at the outset is ani-
mal life, which the plastic force of nature puts
in motion from the most insignificant begin-
nings!
The above particulars you may perceive to-
wards the close of the third day, with very
great attention, and under favour of a bright
light (as of the sun), or with the assistance of a
magnifying glass. Without these aids you would
strain your eyes in vain, so slender is the pur-
ple line, so slight is the motion of the palpitat-
ing point. But at the beginning of the fourth
day you may readily, and at its close most
readily, perceive the "palpitating bloody point,
which already moves," says Aristotle, "like an
animal, in the transparent liquid (which I call
colliquamentum) ; and from this point two vas-
cular branches proceed, full of blood, in a wind-
ing course" into the purpurescent circle and the
investing membrane of the resolved liquid ; dis-
tributing in their progress numerous fibrous
offshoots, which all proceed from one original,
like the branches and twigs of a tree from the
same stem. Within the entering angle of this
root, and in the middle of the resolved liquid,
is placed the red palpitating point, which keeps
order and rhythm in its pulsations, composed of
systoles and diastoles. In the diastole, when it
has imbibed a larger quantity of blood, it be-
comes enlarged, and starts into view; in the
systole, however, subsiding instantaneously as
if convulsed by the stroke, and expelling the
blood, it vanishes from view.
Fabricius depicts this palpitating point in his
third figure; and mistakes it — a thing which is
extraordinary— for the body of the embryo; as
if he had never seen it leaping or pulsating, or
had not understood, or had entirely forgotten
the passage in Aristotle. A still greater subject
of amazement, however, is his total want of so-
licitude about his chalazae all this while, al-
though he had declared the rudiments of the
embryo to be derived from them.
Ulyssus Aldrovandus, writing from Bologna
nearly at the same time, says: "There appears
in the albumen, as it were, a minute palpitating
point, which The Philosopher declares to be the
heart. And I have unquestionably seen a venous
trunk arising from this, from which two other
branches proceeded; these are the blood-ves-
sels, which he says extend to either investing
membrane of the yelk and white. And I am
myself entirely of his opinion, and believe these
to be veins, and pulsatile, and to contain a purer
kind of blood, adapted to the production of the
principal parts of the body, the liver, to wit,
the lungs, and others of the same description."2
Both of the vessels in question, however, are
not veins, neither do they both pulsate; but
one of them is an artery, another a vein, as we
shall see by and by, when we shall further show
that these passages constitute the umbilical
vessels of the embryo.
Volcher Goiter has these words: "The san-
guineous point or globule, which was formerly
found in the yelk, is now observed more in the
albumen, and pulsates distinctly." He says, er-
roneously, "formerly found in the yelk"; for
the point discovered in the vitellus is white,
and does not pulsate; nor does the sanguineous
point or globe appear to pulsate at the end of
the second day of incubation. But the point
which we have indicated in the middle of the
circle, and as constituting its centre in connex-
ion with the vitellus, disappears before that
point which is characterized by Aristotle as pal-
pitating, can be discerned; or, as I conceive,
having turned red, begins to pulsate. For both
points are situated in the centre of the resolved
fluid, and near the root of the veins which
a Orntthologia, xiv, p. 217,
ANIMAL GENERATION
369
thence arise; but they are never seen simultan-
eously: in the place of the white point there ap-
pears a red and palpitating point.
That portion of Goiter's sentence, however,
where he says: "the punctus saliens is now seen
in the albumen rather than in the yelk," is per-
fectly accurate. And, indeed, moved by these
words, I have inquired whether the white point
in question is turned into the blood-red point,
inasmuch as both are nearly of the same size,
and both make their appearance in the same
situation. And I have, indeed, occasionally
found an extremely delicate bright purple cir-
cle ending near the ruddy horizon surrounding
the resolved liquid, in the centre of which there
was the white point, but not the red and pul-
sating point apparent; for I have never ob-
served these two points at one and the same
time. It were certainly of great moment to de-
termine: whether or not the blood was extant
before the pulse? and whether the pulsating
point arose from the veins, or the veins from
the pulsating point ?
So far as my observations enable me to con-
clude, the blood has seemed to go before the
pulse. This conclusion is supported by the
following instance: on Wednesday evening I set
three hen's eggs, and on Saturday evening,
somewhat before the same hour, I found these
eggs cold, as if forsaken by the hen: having
opened one of them, notwithstanding, I found
the rudiments of an embryo, viz., a red and
sanguinolent line in the circumference; and in
the centre, instead of a pulsating point, a white
and bloodless point. By this indication I saw
that the hen had left her nest no long time be-
fore; wherefore, catching her, and shutting her
up in a box, I kept her upon the two remaining
eggs, and several others, through the ensuing
night. Next morning, very early, both of the
eggs with which the experiment was begun, had
revived, and in the centre there was the pul-
sating point, much smaller than the white
point, from which, like a spark darting from a
cloud, it made its appearance in the diastole; it
seemed to me, therefore, that the red point
emanated from the white point; that the punc-
tum saliens was in some way engendered in that
white point; that the punctum saliens, the
blood being already extant, was either origin-
ally there produced, or there began to move. I
have, indeed, repeatedly seen the punctum sa-
liens when all but dead, and no longer giving
any signs of motion, recover its pulsatile move-
ments under the influence of renewed warmth.
In the order of generation, then, I conceive that
the punctum and the blood first exist, and that
pulsation only occurs subsequently.
This at all events is certain, that nothing
whatever of the future foetus is apparent on this
day, save and except certain sanguineous lines,
the punctum saliens, and those veins that all pre-
sent themselves as emanating from a single trunk
(as this itself proceeds from the punctum sa-
liens), and are distributed in numerous branches
over the whole of the colliquament or dissolved
fluid. These vessels afterwards constitute the
umbilical vessels, by means of which, distri-
buted far and wide, the foetus as it grows ob-
tains its nourishment from the albumen and
vitellus. You have a striking example of similar
vessels and their branchings in the leaves of
trees, the whole of the veins of which arise from
the peduncle or foot-stalk, and from a single
trunk are distributed to the rest of the leaf.
The entire including membrane of the colli-
quament traversed by blood-vessels, corres-
ponds in form and dimensions with the two
wings of a moth; and this, in fact, is the mem-
brane which Aristotle describes as "possessing
sanguineous fibres, and at the same time con-
taining a limpid fluid, proceeding from those
mouths of the veins."1
Towards the end of the fourth day, and the
beginning of the fifth, the blood-red point, in-
creased into a small and most delicate vesicle, is
perceived to contain blood in its interior, which
it propels by its contractions, and receives anew
during its diastoles.
Up to this point I have not been able to per-
ceive any difference in the vessels: the arteries
are not distinguished from the veins, either by
their coats or their pulsations. I am therefore of
opinion that all the vessels may be spoken of
indifferently under the name of veins, or, adopt-
ing Aristotle's2 term, of venous canals.
"The punctum saliens," says Aristotle, "is
already possessed of spontaneous motion, like
an animal.*' Because an animal is distinguished
from that which is none, by the possession of
sense and motion. When this point begins to
move for the first time, consequently, we say
well that it has assumed an animal nature; the
egg, originally imbued with a vegetative soul,
now becomes endowed in addition with a mo-
tive and sensitive force; from the vegetable it
passes into the animal; and at the same time the
living principle, which fashions the chick from
the egg, and afterwards gives it the measure of
intelligence it manifests, enters into the em-
bryo. For, from the actions or manifestations,
1 Loc. supra cit. 2 Ibid.
370
WILLIAM HARVEY
The Philosopher1 concludes demonstratively,
that the faculties or powers of acting are inher-
ent, and through these the cause and principle
of life, the soul, to wit, and the actions, inas-
much as manifestation is action.
I am myself further satisfied from numerous
experiments, that not only is motion inherent
in the punctum saliens, which indeed no one
denies, but sensation also. For on any the
slightest touch, you may see the point variously
commoved, and, as it were, irritated; just as
sensitive bodies generally give indications of
their proper sensations by their motions; and,
the injury being repeated, the punctum be-
comes excited and disturbed in the rhythm and
order of its pulsations. Thus do we conclude that
in the sensitive-plant, and in zoophytes, there is
inherent sensibility, because when touched they
contract, as if they felt uncomfortable.
I have seen, I repeat, very frequently, and
those who have been with me have seen this
punctum, when touched with a needle, a probe,
or a finger, and even when exposed to a higher
temperature, or a severer cold, or subjected to
any other molesting circumstance or thing,
give various indications of sensibility, in the
variety, force, and frequency of its pulsations.
It is not to be questioned, therefore, that this
punctum lives, moves, and feels like an animal.
An egg, moreover, too long exposed to the
colder air, the punctum saliens beats more
slowly and languidly; by the finger, or some
other warmth being applied, it forthwith re-
covers its powers. And further, after the punc-
tum has gradually languished, and, replete with
blood, has even ceased from all kind of motion,
or other indication of life, still, on applying my
warm finger, in no longer a time than is meas-
ured by twenty beats of my pulse, lo! the little
heart is revivified, erects itself anew, and, re-
turning from Hades as it were, is restored to its
former pulsations. The same thing happens
through heat applied in any other way— that of
the fire, or of hot water — as has been proved by
myself and others again and again; so that it
seemed as if it lay in our power to deliver the
poor heart over to death, or to recall it to life
at our will and pleasure.
What has now been stated, for the most part
comes to pass on the fourth day from the com-
mencement of the incubation — I say, for the
most part, because it is not invariably so, inas-
much as there is great diversity in the maturity
of eggs, and some are more speedily perfected
than others. As in trees laden with fruit, some,
1 On the Soul
more forward and precocious, fells from the
branches, and some, more crude and immature,
still hangs firmly on the bough; so are some eggs
less forward on the fifth day than others in the
course of the third. This, that I might give it
forth as a thing attested and certain, I have re-
peatedly ascertained in numerous eggs, incu-
bated for the same length of time, and opened
on the same day. Nor can I ascribe it to any dif-
ference of sex, or inclemency of weather, or
neglect of incubation, or to any other cause but
an inherent weakness of the egg itself, or some
deficiency of the native heat.
Hypenemic or unfruitful eggs, begin to change
at this time, as the critical day when they must
show their disposition. As fertile eggs are
changed by the inherent plastic force into col-
liquament (which afterwards passes into blood),
so do wind-eggs now begin to change and to
putrefy. I have, nevertheless, occasionally ob-
served the spot or cicatricula to expand consid-
erably even in hypenemic eggs, but never to
rise into a cumulus, nor to become circum-
scribed by regularly disposed concentric circles.
Sometimes I have even observed the vitellus to
get somewhat clearer, and to become liquefied;
but this was unequally; there were flocks, as if
formed by sudden coagulation, swimming dis-
persed through it like clouds. And although
such eggs could not yet be called putrid, nor
were they offensive, still were they disposed to
putrefaction; and, if continued under the hen,
they soon arrived at this state, the rottenness
commencing at the very spot where in fruitful
eggs the reproductive germ appears.
The more perfect or forward eggs then,
about the end of the fourth day, contain a dou-
ble or bipartite pulsating vesicle, each portion
reciprocating the other's motion, in such order
and manner that whilst one is contracting, the
other is distended with blood and ruddy in col-
our; but this last contracting anon forces out its
charge of blood, and, an instant being inter-
posed, the former rises again and repeats its
pulse. And it is easy to perceive that the action
of these vesicles is contraction, by which the
blood is moved and propelled into the vessels.
"On the fourth day," says Aldrovandus,2
"two puncta are perceived, both of which are in
motion; these, undoubtedly, are the heart and
the liver, viscera which Aristotle allowed to
eggs incubated for three days.**
The Philosopher,3 however, nowhere says
anything of the kind; neither, for the most
2 Op. cit.t ]
i of Animals, in. 4.
ANIMAL GENERATION
371
part, are the viscera mentioned conspicuous be-
fore the tenth day. And I am indeed surprised
that Aldrovandus should have taken one of
these pulsating points for the liver, as if this
viscus were ever moved in any such manner! It
seems much better to believe that with the
growth of the embryo one of the pulsating
points is changed into the auricles, the other into
the ventricles of the heart. For in the adult, the
ventricles are filled in the same manner by the
auricles, and by their contraction they are
straightway emptied again, as we have shown in
our treatise On the Motion of the Heart and Blood.
In more forward eggs, towards the end of the
fourth day, I have occasionally found I know
not what cause of obscurity intervening and
preventing me from seeing these pulsating vesi-
cles with the same distinctness as before; it was
as if there had been a haze interposed between
them and the eye. In a clearer light, neverthe-
less, and with the use of magnifying glasses, the
observations of one day being further collated
with those of the next succeeding day, it was
discovered that the indistinctness was caused
by the rudiments of the body-— a nebula con-
cocted from part of the colliquament, or an
effluvium concreting around the commence-
ments of the veins.
Aldrovandus appears to have observed this:
"On the fifth day,'* says he, "the punctum,
which we have stated to be the heart, is no
longer seen to move externally, but to be cov-
ered over and concealed; still its two meatus
venosi are perceived more distinctly than be-
fore, one of them being, further, larger than
the other." But our learned author was mis-
taken here; for this familiar divinity, the heart,
enters into his mansion and shuts himself up in
its inmost recesses a long time afterwards, and
when the house is almost completely built. Al-
drovandus also errs when he says, "by the vis
insita of the veins, the remaining portion of the
albumen acquires a straw colour," for this col-
our is observed in the thicker albumen of every
spoilt egg, and it goes on increasing in depth
from day to day as the egg grows staler, and
this without any influence of the veins, the
thinner portion only being dissipated.
But the embryo enlarging, as we say below,
and the ramifications of the meatus venosi ex-
tending far and wide to the albumen and vitel-
lus, portions of both of these fluids become liq-
uefied, not indeed in the way Aldrovandus will
have it, from some vis insita in the vessels, but
from the heat of the blood which they contain.
For into whatsoever part of either fluid the ves-
sels in question extend, straightway liquefac-
tion appears in their vicinity; and it is on this
account that the yelk about this epoch appears
double: its superior portion, which is in juxta-
position with the blunt end of the egg, has al-
ready become more diffluent than the rest, and
appears like melted yellow wax in contrast with
the other colder firmer portion; like bodies in
general in a state of fusion, it also occupies a
larger space. Now this superior portion, lique-
fied by the genial heat, is separated from the
other liquids of the egg, but particularly the al-
bumen, by a tunica propria of extreme tenuity.
It therefore happens that if this most delicate,
fragile, and invisible membrane be torn, im-
mediately there ensues an admixture and con-
fusion of the albumen and vitellus, by which
everything is obscured. And such an accident
is a frequent cause of failure in the reproduc-
tive power (for the different fluids in question
are possessed of opposite natures), according to
Aristotle,1 in the place already so frequently re-
ferred to: "Eggs are spoiled and become addled
in warm weather especially, and with good rea-
son; for as wine grows sour in hot weather, the
lees becoming diffused through it (which is the
cause of its spoiling), so do eggs perish when the
yelk spoils, for the lees and the yelk are the
more earthy portion in each. Wherefore wine
is destroyed by an admixture with its dregs,
and an egg by the diffusion of its yelk."2 And
here, too, we may not improperly refer to that
passage where he says: "When it thunders, the
eggs that are under incubation are spoiled"3;
for it must be a likely matter that a membrane
so delicate should give way amidst a conflict of
the elements. And perhaps it is because thunder
is frequent about the dog-days that eggs which
are rotten have been called cynosura; so that
Columella rightly informs us that "the summer
solstice, in the opinion of many, is not a good
season for breeding chickens."
This at all events is certain, that eggs are very
readily shaken and injured when the fowls are
disturbed during incubation, at which time the
fluids are liquefied and expanded, and their
containing membranes are distended and ex-
tremely tender.
EXERCISE 18. The fourth inspection of the egg
"In the course of the fifth day of incuba-
tion," says Aristotle,4 "the body of the chick
is first distinguished, of very small dimensions
1 On the Generation of Animals, in. 2.
2 History of Animals, vi. 2.
9 Ibid., vni. 5. * Ibid., vi. 3.
372
WILLIAM HARVEY
indeed, and white; but the head conspicuous
and the eyes extremely prominent, a state in
which they afterwards continue long; for they
only grow smaller and shrink at a later period.
In the lower portion of the body there is no
rudimentary member corresponding with what
is seen in the upper part. But of the channels
which proceed from the heart, one now tends
to the investing membrane, the other to the
yelk; together they supply the office of an um-
bilical cord. The chick, therefore, derives its
origin from the albumen, but it is afterwards
nourished by the yelk, through the umbilicus."
These words of Aristotle appear to subdivide
the entire generation of the chick into three
stages or periods, viz. : from the first day of the
incubation to the fifth; from thence on to the
tenth or fourteenth: and from this or that to
the twentieth. It seems as if he had only given
an account in his history of the circumstances
he observed at these three epochs; and it is then
indeed that the greatest changes take place in
the egg; as if these three critical seasons, or
these three degrees in the process which leads
from the perfect egg to the evolution of the
chicken, were especially to be distinguished.
On the fourth day the first particle of the em-
bryo appears, viz. : the punctum saliens and the
blood; and then the new being is incorporated.
On the seventh day the chick is distinguished
by its extremities, and begins to move. On the
tenth it is feathered. About the twentieth it
breathes, chirps, and endeavours to escape. The
life of the egg, up to the fourth day, seems iden-
tical with that of plants, and can only be ac-
counted as of a vegetative nature. From this
onwards to the tenth day, however, like an ani-
mal, it is possessed by a sensitive and motive
principle, with which it continues to increase,
and is afterwards gradually perfected, becom-
ing covered with feathers, furnished with a
beak, nails, and all else that is necessary to its
escape from the shell; emancipated from which,
it enters at length on its own independent exist-
ence.
Of the incidents that happen after the fourth
day, Aristotle enumerates three particularly,
viz. : the construction of the body; the distribu-
tion of the veins, which have already the office
and nature of the umbilicus; and the matter
whence the embryo first arises, and is con-
stituted and nourished.
In reference to the structure of the body, he
speaks of its size and colour, of the parts which
are most conspicuous in it (the head and eyes),
and of the distinction of its extremities.
The body is indeed extremely minute, and of
the form of the common maggot that gives
birth to the fly ; it is of a white colour, too, like
the maggot of the flesh-fly which we see cher-
ished and nourished in putrid meat. He hap-
pily adds, "it is most remarkable for its head
and eyes." For what first appears is homogen-
eous and indistinct, a kind of concretion or
coagulation of the colliquament, like the jelly
prepared from hartshorn; it is a mere trans-
parent cloud, and scarcely recognizable, save as
it appears, divided, seemingly, into two parts,
one of which is globular and much larger than
the other; this is the rudiment of the head,
which first becomes visible on the fifth day,
very soon after which the eyes are distinguish-
able, being from the first of large size and prom-
inent, and marked off from the rest of the head
and body by a certain circumfusion of black
matter. Either of the eyes is larger than the
whole of the rest of the head, in the same way
as the head surpasses the remainder of the body
in dimensions. The whiteness of the body, and
prominence of the eyes (which, as well as the
brain, are filled internally with perfectly pel-
lucid water, but externally are of a dark colour)
continue for some time— up to the tenth day,
and even longer; for, as we have seen, Aristotle
says that "the eyes decrease at a late period,
and contract to the proper proportion." But
for my own part, I do not think that the eyes of
birds ever contract in the same ratio which we
observe between the head and eyes of a vivi-
parous animal. For if you strip off the integu-
ments from the head and eyes of a fowl or an-
other bird, you will perceive one of the eyes to
equal the entire brain in dimensions; in the
woodcock and others, one of the eyes indeed is
as large as the whole head, if you make abstrac-
tion of the bill. But this is common to all birds
that the orbit or cavity which surrounds the
eye is larger than the brain, a fact that is ap-
parent in the cranium of every bird. Their
eyes, however, are made to look smaller, be-
cause every part, except the pupil, is covered
with skin and feathers; neither are they pos-
sessed of such a globular form as would cause
them to project; they are of a flatter configura-
tion, as in fishes.
"In the lower part of the body," says the
Philosopher, "we perceive the rudiments of no
member corresponding with the superior mem-
bers." And the thing is so in fact; for as the
body at first appears to consist of little but head
and eyes, so interiorly there is neither any ex-
tremity— wings, legs, sternum, rump — nor any
ANIMAL GENERATION
373
viscus apparent; the body indeed is still with-
out any kind of proper form; in so far as I am
able to perceive, it consists of a small mass ad-
jacent to the vein, like the bent keel of a boat,
like a maggot or an ant, without a vestige of
ribs, wings, or feet, to which a globular and
much more conspicuous mass is appended, the
rudiment of the head, to wit, divided, as it
seems, into three vesicles when regarded from
either side, but in fact consisting of four cells,
two of which, of great size and a black colour,
are the rudiments of the eyes; of the remaining
two one being the brain, the other the cerebel-
lum. All of these are full of perfectly limpid
water. In the middle of the blackness of the
eye, the pupil is perceived shining like a trans-
parent central spark or crystal. I imagine that
three of these vesicles being particularly con-
spicuous, has been the cause of indifferent ob-
servers falling into error. For as they had
learned from the schoolmen that there was a
triple dominion in the animal body, and they
believed that these principal parts, the brain,
the heart, and the liver, performed the highest
functions in the economy, they easily per-
suaded themselves that these three vesicles
were the rudiments and commencements of
these parts. Goiter, however, as becomes an ex-
perienced anatomist, affirms more truly that
whilst he had observed the beak and eyes from
the seventh day of incubation, he could yet dis-
cover nothing of the viscera.
But let us hear the Philosopher further: "Of
the conduits which lead from the heart, one
tends to the investing membrane, another to
the yelk, in order to perform the office of um-
bilicus." The embryo having now taken shape,
these veins do indeed perform the function of
the umbilical cord, the ramifications of one of
them proceeding to be distributed to the outer
tunic which invests the albumen, those of the
other running for distribution to the vitellary
membrane and its included fluid. Whence it
clearly appears that both of these fluids are
alike intended for the nourishment of the em-
bryo. And although Aristotle says that "the
chick has its commencement in the albumen,
and is nourished through the umbilicus by the
yelk," he still does not say that the chick is
formed from the albumen. The embryo, in
fact, is formed from that clear liquid which we
have spoken of under the name of the colliqua-
ment, and the whole of what we have called
the eye of the egg is contained or included
within the albumen. Neither does our author
say that the whole and sole nutriment of the
embryo reaches it through the umbilicus. My
own observations lead me to interpret his
words in this way: although the embryo of the
fowl begins to be formed in the albumen, never-
theless it is not nourished solely by that, but also
by the yelk, to which one of the two umbilical
conduits pertains, and from whence it derives
nourishment in a more especial manner; for the
albumen, according to Aristotle's opinion, is
the more concoct and purer liquid, the yelk the
more earthy and solid one, and, therefore, more
apt to sustain the chick when it has once at-
tained to greater consistency and strength; and
further because, as shall be explained below,
the yelk supplies the place of milk, and is the
last part that is consumed, a residuary portion,
even after the chick is born, and when it is fol-
lowing its mother, being still contained in its
abdomen.
What has now been stated takes place from
the fourth to the tenth day. I have yet to speak
of the order and manner in which each of the
particulars indicated transpires.
In the inspection made on the fifth day, we
observed around the short vein which proceeds
from the angle where the two alternately pul-
sating points are situated, something whiter
and thicker, like a cloud, although still trans-
parent, through which the vein just mentioned
is seen obscurely, and, as it were, through a
haze. The same thing I have occasionally seen
in the more forward eggs in the course of the
fourth day. Now this is the rudiment of the
body, and from hour to hour it goes on increas-
ing in compactness and solidity; both surround-
ing the afore-named vein, and being appended
to it in the guise of a kind of globule. This glob-
ular rudiment far exceeds the coronal portion,
as I shall call it, of the vermicular body; it is
triangular in figure, being obscurely divided
into three parts, like so many swelling buds of a
tree. One of these is orbicular and larger than
either of the other two; and it is darkened by
most delicate filaments proceeding from the
circumference to the centre; this appears to be
the commencement of the ciliary body, and
therefore proclaims that this is the part which
is to undergo transformation into the eye. In
its middle the minute pupil, shining like a
bright point, as already stated, is conspicuous;
and it was from this indication especially that I
ventured to conjecture that the whole of the
globular mass was the rudiment of the future
head, and this black circle one of the eyes, hav-
ing the other over against it; for the two are so
situated that they can by no means be seen at
374
WILLIAM HARVEY
once and together, one always lying over and
concealing the other.
The first rudiment of the future body, which
we have stated to sprout around the vein, ac-
quires an oblong and somewhat bent figure,
like the keel of a boat. It is of a mucaginous con-
sistence, like the white mould that grows upon
damp things excluded from the air. The vein to
which this mucor attaches, as I have said, is the
vena cava, descending along the spinal column,
as my subsequent observations have satisfied
me. And if you carefully note the order of con-
traction in the pulsating vesicles, you may see
the one which contracts last impelling its blood
into the root of this vein and distending it.
Thus there are two manifest contractions
and two similar dilatations in the two vesicles
which are seen moving and pulsating alternate-
ly; and the contraction of the one which pre-
cedes causes the distension or dilatation of the
other; for the blood escapes from the cavity of
the former vesicle, when it contracts, into that
of the latter, which it fills, distends, and causes
to pulsate; but this second vesicle, contracting
in its turn, throws the blood, which it had re-
ceived from the former vesicle, into the root of
the vein aforesaid, and at the same time dis-
tends it. I go on speaking of this vessel as a vein,
though from its pulsation I hold it to be the
aorta, because the veins are not yet distin-
guished from the arteries by any difference in
the thickness of their respective coats.
After having contemplated these points with
great care, and in many eggs, I remained for
some time in suspense as to the opinion I should
adopt; whether I should conclude that the con-
crete appended globular mass proceeded from
the colliquament in which it swam, becoming a
compacted and coagulated matter in the way
that clouds are formed from invisible vapour
condensed in the upper regions of the air; or
believe that it took its rise from a certain efflu-
vium exhaled from the sanguineous conduit
mentioned, originating by diapedesis or trans-
udation, and by deriving nourishment from
thence, was enabled to increase. For the be-
ginnings of even the greatest things are often
extremely small, and, by reason of this minute-
ness, sufficiently obscure.
This much I think I have sufficiently deter-
mined at all events, war,, that the puncta salien-
tia and meatus venosi, and the vena cava itself,
are the parts that first exist; and that the globu-
lar mass mentioned afterwards grows to them.
I am further certain that the blood is thrown
from the punctum saliens into the vein, and
that from this does the corpuscle in question
grow, and by this is it nourished. The fungus or
mucor first originates from an effluvium of the
vein on which it appears, and it is thence nour-
ished and made to increase; in the same way as
mouldiness grows in moist places, in the dark
corners of houses which long escape cleansing;
or, like camphor upon cedar wood tables, and
moss upon rocks and the bark of trees; lastly, as
a kind of delicate down grows upon certain
grubs.
Upon the same occasion I also debated with
myself whether or not I should conclude, that
with the coagulation of the colliquament ac-
complished, the rudiments of the head and
body existed simultaneously with the punctum
saliens and the blood, but in a pellucid state,
and so delicate that they almost escaped the
eye, until becoming inspissated into a fungus or
mucor, they acquired a more opaque white
colour, and then came into view; the blood
meantime from its greater spissitude and pur-
ple colour being readily perceptible in the dia-
phanous colliquament. But now when I look at
the thing more narrowly, I am of opinion that
the blood exists before any particle of the body
appears; that it is the first-born of all the parts
of the embryo; that from it both the matter
out of which the foetus is embodied, and the
nutriment by which it grows are derived; that
it is in fine, if such thing there be, the primary
generative particle. But wherefore I am led to
adopt this idea shall afterwards be shown more
at length when I come to treat of the primary
genital part, of the innate heat, and the radical
moisture; and, at the same time, conclude as to
what we are to think of the vital principle
(anima), from a great number of observations
compared with one another.
About this period almost every hour makes
a difference; every thing grows larger, more def-
inite and distinct; the rate of change in the
egg is rapid, and one change succeeds immedi-
ately upon the back of another. The cavity in
the egg is now much larger, and the whole of its
upper portion is empty; it is as if a fifth part of
the egg had been removed.
The ramifications of the veins extend more
widely, and are more numerous, not only in the
colliquament as before, but they spread on one
hand into the albumen, and on the other into
the yelk, so that both of these fluids are every-
where covered over with blood-vessels. The up-
per portion of the yelk has now become much
dissolved, so that it very obviously differs from
the lower portion; there are now, as it were,
ANIMAL GENERATION
375
two yelks, or two kinds of yelk; whilst the
superior, like melted wax, is expanded and
looks pellucid, the inferior has become more
dense, and with the thicker portion of the al-
bumen has subsided to the sharp end of the egg.
The tunica propria of the upper portion of the
yelk is so thin that it gives way on the slightest
succussion, when there ensues admixture of the
fluids, and, as we have said, interruption to the
further progress of the process of generation.
And now it is that the rudiments of the em-
bryo first become conspicuous, as may be seen
in the fifth and sixth figure of Fabricius; the
egg being put into fair water it will be easy to
perceive what parts of the body are formed,
what are still wanting. The embryo now pre-
sents itself in the form of a small worm or mag-
got, such as we encounter on the leaves of trees,
in spots of their bark, in fruit, flowers, and else-
where; but especially in the apples of the oak,
in the centre of which, surrounded with a case,
a limpid fluid is contained, which, gradually in-
spissated and congealed, acquires a most delicate
outline, and finally assumes the form of a maggot ;
for some time, however, it remains motionless;
but by and by, endowed with motion and sen-
sation it becomes an animal, and subsequently it
breaks forth and takes its flight as a fly.
Aristotle ascribes a similar mode of produc-
tion to those creatures that are spontaneously
engendered. "Some are engendered of the
dew," he says, "which falls upon the leaves."
And by and by he adds, "butterflies are engen-
dered from caterpillars, but these, in their turn,
spring from green leaves, particularly that
species of raphanus which is called cabbage.
They are smaller than millet seeds at first, and
then they grow into little worms; next, in the
course of three days into caterpillars; after
which they cease from motion, change their
shape, and pass into chrysalides, when they are
inclosed in a hard shell; although, if touched,
they will still move. The shell after a long time
cracks and gives way, and the winged animal,
which we call a butterfly, emerges."1
But our doctrine— and we shall prove it by
and by — is, that all animal generation is ef-
fected in the same way; that all animals, even
the most perfect, are produced from worms; a
fact which Aristotle himself seems to have
noted when he says: "In all, nevertheless, even
those that lay perfect eggs, the first conception
grows whilst it is yet invisible; and this, too, is
the nature of the worm."2 For there is this dif-
1 History of Animals, v. 19.
2 On the Generation of Animals, in. 9.
ference between the generation of worms and of
other animals, that the former acquire dimen-
sions before they have any definite form or are
distinguished into parts, in conformity with
what the philosopher says in the following sen-
tence: "An animal is fashioned from an entire
worm, not from any one particular part, as in
the case of an egg, but the whole increases and
becomes an articulated animal,"3 /. <?., in its
growth it separates into parts.
It is indeed matter worthy of admiration
that the rudiments of all animals, particularly
those possessed of red blood, such as the dog,
horse, deer, ox, common fowl, snake, and even
man himself, should so signally resemble a mag-
got in figure and consistence, that with the eye
you can perceive no difference between them.
Towards the end of the fifth day or the be-
ginning of the sixth, the head is divided into
three vesicles: the first of these, which is also
the largest, is rounded and black; this is the
eye, in the centre of which the pupil can be dis-
tinguished like a crystalline point. Under this
there lies a smaller vesicle, concealed in part,
which represents the brain; and over this lies
the third vesicle, like an added crest or rounded
summit crowning the whole, from which the
cerebellum is at length produced. In the whole
of these there is nothing to be discovered but a
little perfectly limpid water.
And now the rudiment of the body, which
we have called the carina, distinctly proclaims
itself to be the spinal column, to which sides
soon begin to be added, and the wings and the
lower extremities present themselves, project-
ing slightly from the body of the maggot. The
venous conduits are, further, now clearly refer-
rible to the umbilical vessels.
EXERCISE 19. The fifth inspection of the egg
On the sixth day the three cells of the head
present themselves more distinctly, and the
coats of the eyes are now apparent; the legs and
the wings also bud forth, much in the way in
which, towards the end of June, we see tadpoles
getting their extremities, when they quit the
water, and losing their tails assume the form of
frogs.
In the chick, the rump has still no other form
than is conspicuous in animals at large, even in
serpents; it is a round and slender tail. The sub-
stance of the heart now grows upon the pulsat-
ing vesicle; and shortly afterwards the rudi-
ments of the liver and lungs are distinguished;
the bill, too, makes its appearance at the same
1 History of Animals, v. 19.
376
time. Everything is of a pure white colour, es-
pecially the bill. About the same epoch all the
viscera and the intestines are conspicuous. But
the heart takes precedence of all the parts; and
the lungs are visible before the liver or brain.
The eyes, however, are seen first of all, by rea-
son of their large size and black colour.
And now, too, the embryo has a power of
motion, and raises its head and slightly twists it-
self, although there is still nothing of the brain
to be seen, but only a little limpid fluid inclosed
in a vesicle. It is at length a perfect maggot,
only differing from a caterpillar in this, that
when worms are set free from their cells they
creep about hither and thither and seek their
food, whilst the worm in the egg is stationary,
and, surrounded with its proper food, is fur-
nished with aliment through the umbilicus.
The viscera and intestines being now formed,
and the foetus able to execute motions, the an-
terior portion of the body, without either
thorax or abdomen, is perceived to be com-
pletely open; so that the heart itself, the liver
and the intestines, are seen to hang pendulous
externally.
Towards the end of this day and the begin-
ning of the seventh, the toes are distinguished,
and the embryo already presents the outlines
of the chick, and opens its beak, and kicks
with its feet; in short, all the parts are sketched
out, but the eyes, above all, are conspicuous.
The viscera, on the contrary, are so indistinct,
that Goiter affirms, that whilst he plainly saw
the eyes and beak he could discover no viscus,
even obscurely and confusedly shadowed forth.
The changes that take place from the begin-
ning of the sixth to the end of the seventh day,
occur for the major part in some eggs more
quickly, in others a little more tardily. The
coats of the eyes are now visible, but they only
include a colourless and limpid fluid in their in-
terior. The eyes themselves project somewhat
beyond their orbits, and each of them does not
less exceed the brain in size, than the head with
which they are connected exceeds the whole of
the rest of the body.
The vesicle, which like a ridge or crest ex-
pands beyond the confines of the brain, occu-
pies the place of the cerebellum; and, like the
other vesicles, is filled with a transparent fluid.
The brain is perceived to be obscurely bipar-
tite, and refracts the light less than the cerebel-
lum, though it is of a whiter colour. And as the
heart is seen lying without the confines of the
thorax, so likewise does the cerebellum pro-
trude beyond the limits of the head.
WILLIAM HARVEY
If the head be removed, the vessels ascending
to the brain may be observed as bloody points,
with the use of a magnifying glass. And now,
too, the rudiments of the spine begin to be first
perceived distinct from the rest of the pulp, of a
milky colour, but firmer consistence. So in the
same way, and like flimsy threads of a spider's
web, the ribs and other bones make their ap-
pearance in the guise of milky lines, amidst the
pulp of the body; and the same thing appears
more clearly in the formation of the larger ovi-
parous animals. The heart, lungs, liver, and by
way of intestines certain most delicate fila-
ments, all present themselves of a white colour.
The parenchyma of the liver is developed upon
delicate fibrous stamens over the umbilical vein
at the part where it enters, almost in the same
manner as we have said that the rudiments of
the body grow to the vein descending from the
heart, or the vesicula pulsans. For in the same
way as grapes grow upon the stalk of the bunch,
buds upon twigs, and the ear upon the straw,
does the liver adhere to the umbilical vein, and
arise from it, even as fungi do from trees and
excessive granulations from ulcers, or as sarcoses
or morbid growths spring around the minute
branches of conterminous arteries by which
they are nourished, and occasionally attain to
an excessive size.
Looking back upon this office of the arteries,
or the circulation of the blood, I have occasion-
ally and against all expectation completely
cured enormous sarcoceles, by the simple means
of dividing or tying the little artery that sup-
plied them, and so preventing all access of
nourishment or spirit to the part affected; by
which it came to pass that the tumour, on the
verge of mortification, was afterwards easily
extirpated with the knife, or the searing iron.
One man in particular (and this case I can con-
firm by the testimony of many respectable
persons) had an enormous hernia carnosa, or
sarcocosis of the scrotum, larger than a human
head, and hanging as low as the knee; from its
upper part a fleshy mass, of the thickness of the
wrist, or such a rope as is used on ship- board,
extended into the abdomen; and the evil had
attained to such a height, that no one durst at-
tempt the cure, either with the knife or any
other means. Nevertheless, by the procedure
above indicated, I succeeded in completely re-
moving this huge excrescence which distended
the scrotum, and involved the testicle in its
middle; this latter organ, with its vas praepar-
ans and vas deferens, and other parts which
descend in the tunica vaginalis, being left all
ANIMAL GENERATION
377
the while safe and uninjured. But this cure, as
well as various others, accomplished in opposi-
tion to vulgar opinion and by unusual proced-
ures, I shall relate at greater length in my Medi-
cal Observations, if God grant me longer life.
I mention such cases with a view of more
clearly showing that the liver grows upon the
vessels, and is only developed some time after
the appearance of the blood; that its parenchy-
ma is derived from the arteries whence the mat-
ter is effused, and that for a while it remains
white and bloodless, like various other parts of
the body. Now in the same manner and order
precisely as the chick is developed from the
egg, is the generation of man and other animals
accomplished.
Whence it appears that the doctrine which
makes the liver the author and fashioner of the
blood, is altogether groundless, although both
formerly and at the present time this view ob-
tained universal assent; this was the reason
wherefore the liver was reckoned as among the
principal and first-formed organs of the body.
This viscus indeed was so highly dignified that
it was thought to be produced in the very begin-
ning, and simultaneously with the heart, from
the seminal fluid of the mother; and the medi-
cal fable of the three vesicles or three kids, as
they were called, was eagerly defended. Among
the number of modern abettors of such views,
Pansanus has of late with confidence enough,
but little skill, been singing to the old measure.
These good people do not consider that the ves-
icles are in motion in the egg, that the heart is
palpitating and the blood present and perfectly
concocted, before any sign or vestige of the
liver appears. The blood is much rather to be
accounted the efficient cause of the liver, than
this the author of the blood: for the liver is en-
gendered after the blood, and from it, being
adnate to the vessels that contain it.
But neither can I agree with the Aristotel-
ians, who maintain that the heart is the author
of the blood ; for its parenchyma or proper sub-
stance arises some little time after the blood,
and is superadded to the pulsating vesicles. I
am, however, in much doubt as to whether the
pulsating vesicle or point, or the blood itself
be the older; whether it be the fluid contained,
or the containing sacs. It is obvious, neverthe-
less, that that which contains is formed for the
sake of that which is contained, and is, there-
fore, made later. And this much, upon the
faithful testimony of our eyes, is certain, that
the first particle and prime basis of the body are
the veins, to which all the other parts are post-
humous and superadded. But upon this point
we shall say more by and by.
Meantime we may be permitted to smile at
that factitious division of the parts into sperm-
atic and sanguineous; as if any part were pro-
duced immediately from the seminal fluid, and
all did not spring from the same source!
I return to our subject. The colliquament
now extends over more than half the egg. The
heart, hanging outwards, is at some short dis-
tance from the body. And if you look atten-
tively you may perceive some of the umbilical
vessels pulsating.
EXERCISE 20. The sixth inspection
Everything is still more distinct upon the
seventh day, and the rudiments of several of
the particular parts are now conspicuous, viz.,
the wings, legs, genital organs, divisions for the
toes, thighs, ilia, &c. The embryo now moves
and kicks, and the form of the perfect chick is
recognizable; from this time forward, indeed,
nothing is superadded; the very delicate parts
only increase in size. The more the parts grow
the more is the albumen consumed, and the ex-
ternal membranes united come to be of the na-
ture of the secundines, and ever more and more
closely represent the umbilical cord. Wherefore
I conceive that, from the seventh, we may at
once pass on to the tenth day, nothing of any
moment occurring in this interval which is not
particularly noted by other writers, especially
by Aristotle.
It happens, nevertheless, that when a num-
ber of eggs are examined together, some are
found more precocious and forward, having
everything more distinct; others, again, are
more sluggish, and these have the parts less ap-
parent. The season of the year, the place where
the incubation is carried on, the sedulousness
with which it is performed, and other accidents,
have undoubtedly great influence on this di-
versity of result. I remember on one occasion,
on the seventh day to have seen the cavity in
the blunt end enlarged in a sluggish egg, the
colliquament covered with veins, the vermicu-
lar embryo in its middle, the rudiments of the
eyes, and all the rest as it is met with in the gen-
erality of eggs on the fifth day; but the pulsa-
tory vesicles were not yet apparent, nor was the
trunk or root of the veins from which we have
said that they originate, yet to be discovered. I,
therefore, regarded this egg as of a feeble na-
ture and left behind, as possessed of an inade-
quate reproductive faculty, and near to its
death; all the more when I observed its colliq-
378
WILLIAM HARVEY
uamcnt less pellucid and refractive than usual,
and the vessels not of such a bright red colour as
wont. When the vital spirit is about to escape,
that part which is first influenced in generation
and earliest attracts attention is also the first
that fails and disappears.
EXERCISE 21. The inspection after the tenth day
All that presents itself on the tenth day is so
accurately described by Aristotle that scarcely
anything remains for us to add. Now his opin-
ion, according to my interpretation of it, is this,
viz., that "on the tenth day the entire chick is
conspicuous,"1 being pellucid and white in
every part except the eyes and the venous ram-
ifications. "The head at this time is larger than
the whole of the rest of the body; and eyes
larger than the head are connected with it,"
(adhering, and being in some sort appended to
the head), "but having as yet no pupils" (per-
fectly formed pupils must here be understood,
for it is not difficult to make out the distinct
tunics of the eye at this epoch); "the eyes, if
removed at this time, will be found as large as
beans and black, and if they be incised, a clear
humour flows out, cold, and refracting the light
powerfully, but nothing else," /. <?., in the
whole head there is nothing but the limpid
water which has been mentioned. Such is the
state of matters from the seventh to the tenth
day, as we have said above. "At the same time,"
he continues, "the viscera also appear, and all
that appertains to the abdomen and intestines,"
viz., the substance of the heart, the lungs, liver,
&c., all of a white colour, mucilaginous, pulpy,
without any kind of consistency. "The veins,
too, that issue from the heart are already in
connexion with the umbilicus, from which one
vein extends to the membrane that includes
the vitellus, which has now become more liquid
and diffluent than it was originally; another to
the membrane which surrounds everything"
(/. e., the tunica colliquamenti) "and embraces
the foetus, the vitellus and the interjacent
fluid. For the embryo increasing somewhat, one
portion of the vitellus is superior, another in-
ferior; but the albumen in the middle is liquid,
and still extends under the inferior portion of
the vitellus, as it did previously." Thus far
Aristotle.
And now the arteries are seen distinctly ac-
companying the veins, both those that proceed
to the albumen and those that are distributed
to the vitellus. The vitellus also at this time
liquefies still more and becomes more diffluent,
1 History of AmmaU, vi. 3.
not entirely, indeed, but, as already said, that
portion of it which is uppermost; neither do
the branches of the veins proceed to every part
of the vitellus alike, but only to that part
which we have spoken of as resembling melted
wax. The veins that are distributed to the al-
bumen have, in like manner, arteries accom-
panying them. The larger portion of the albu-
men now dissolves into a clear fluid, the colliq-
uament, which surrounds the embryo that
swims in its middle, and comes between the two
portions of the vitellus, viz., the superior and
the inferior; underneath all (in the sharp end
of the egg), the thicker and more viscid portion
of the albumen is contained. The superior por-
tion of the yelk already appears more liquid
and diffluent than the inferior; and wherever
the branches of the veins extend, there the
matter seems suddenly to swell and become
more diffluent.
"On the tenth day," continues our author,
"the albumen subsides, having now become a
small tenacious, viscid, and yellowish mass" —
so much of it, that is to say, as has not passed
into the state of colliquament.
For already the larger portion of the white
has become dissolved, and has even passed into
the body of the embryo, viz., the whole of the
thinner albumen, and the greater portion of
the thicker. The yelk, on the contrary, rather
looks larger than it did in the beginning. Whence
it clearly appears that the yelk has not as yet
served for the nutrition of the embryo, but is
reserved to perform this office by and by. In so
far as we can conjecture from the course and
distribution of the veins, the embryo from the
commencement is nourished by the colliqua-
ment; upon this blood-vessels are first distrib-
uted, and then they spread over the mem-
brane of the thinner albumen, next over the
thicker albumen, and finally over the vitellus.
The thicker albumen serves for nutriment
after the thinner; the vitellus is drawn upon
last of all.
The delicate embryo, consequently, whilst it
is yet in the vermicular state, is nourished with
the thinnest and best concocted aliment, the
colliquament and thinner albumen; but when
it is older it has food supplied to it more in har-
mony with its age and strength.
Aristotle describes the relative situation of
the several parts in the following words: "In the
anterior and posterior part, the membrane of
the egg lies under the shell — I do not mean the
membrane of the shell itself, but one under
this, in which there is contained a clear fluid"—
ANIMAL GENERATION
379
the colliquament; "then the chick and the
membrane including it, which keeps it distinct
from the fluid around it." But here I suspect
that there is an error in the text; for as the au-
thor himself indicates the thing, it ought rather
to stand thus: "then the chick, enveloped in a
membrane, continues or swims in the clear
fluid"; which membrane is not exterior to the
one that immediately lines the shell, but an-
other lying under this; which, when the first or
external albumen is consumed, and the re-
mainder of the thicker albumen is depressed
into the sharp end of the egg, of two mem-
branes forms a single tunic that now begins to
present itself like the secundine called the
chorion. And Aristotle says well, "there is a
clear fluid contained in it," by which words he
does not mean the albumen, but the colliqua-
ment derived from the albumen, and in which
the embryo swims; for the albumen that re-
mains subsides into the small end of the egg.
EXERCISE 22. The inspection after the fourteenth
day
From the seventh to the fourteenth day
everything has grown and become more con-
spicuous. The heart and all the other viscera
have now become concealed within the abdo-
men of the embryo, and the parts that formerly
were seen naked and projecting externally, can
now only be perceived when the thorax and ab-
domen are laid open. The chick too now begins
to be covered with feathers, the roots of which
are first perceived as black points. The pupils of
the eyes are distinguished; the eyelids appear,
as does also the membrana nictitans in the
greater canthus of the eye, a membrane which
is proper to birds, and which they use for
cleansing the eyeball. The convolutions of the
brain further make their appearance; the cere-
bellum is included within the skull; and the
tail acquires the characteristic shape of the
bird's rump.
After the fourteenth day the viscera, which
up to this time have been white, gradually be-
gin to assume a flesh or reddish colour. The
heart, having now entered the penetralia of the
thorax and been covered with the sternum, in-
habits the dwelling place which itself had
formed. The cerebrum and cerebellum acquire
solidity under the dome of the skull; the stom-
ach and intestines, however, are not yet in-
cluded within the abdomen, but, connected
with the parts within, hang pendulous exter-
nally.
Of the two vessels that proceed from the ab-
domen to the umbilicus, near the anus, one is
an artery, as its pulse proclaims, and arises from
the arteria magna or aorta, the other is a vein,
and extends from the vitellus by the side of the
intestines to the vena portae, situated in the
concave part of the liver. The other trunk of
the umbilical vessels, collecting its branches
from the albumen, passes the convexity of the
liver, and enters the vena cava near the base of
the heart.
As all these things go on becoming clearer
from day to day, so the greater portion of the
albumen is also gradually consumed; this, how-
ever, is nowise the case with the vitellus, which
remains almost entire up to this time, and in-
deed is seen of the same size as it was the first
day.
In the course of the following days five um-
bilical vessels are conspicuous; one of these is
the great vein, arising from the cava above the
liver, and distributing its branches to the albu-
men; two other veins proceed from the porta,
both having the same origin, and run to the
two portions of the vitellus, which we have but
just described; and these are accompanied by
two arteries arising one on either side from the
lumbars.
The chick now occupies a larger space in the
egg than all the rest of the matter included in
it, and begins to be covered with feathers; the
larger the embryo grows, the smaller is the
quantity of albumen that is present. It is also
worthy of observation, that the membrane of
the colliquament which we have said unites
with the external investing membrane, and
constitutes the secundine or chorion, now in-
cludes the whole of the vitellus in one, and be-
coming contracted, draws the vitellus along
with the intestines towards the chick, conjoins
them with its body, and incloses them, as it
were, in a thick sac. Everything that was pre-
viously extremely delicate and transparent, be-
comes more opaque and fleshy as the sac con-
tracts, which at length, like a hernial tumour of
the scrotum, includes and supports both the
intestines and the yelk; contracting every day
in a greater and greater degree, it comes finally,
to constitute the abdomen of the chick. You
will find the yelk, about the eighteenth day,
lying among the intestines, the belly at large
being lax; yet are the parts not so firmly fixed
but that the intestines (as in the case of a scrotal
hernia), along with the vitellus, can be pushed
up into the belly, or forced out of it as it were
into a pouch. I have occasionally seen the
vitellus prolapsed in this way from the ab-
380
WILLIAM HARVEY
dominal cavity of a pigeon, which had been
prematurely excluded from the shell in the
summer season.
The chick at this epoch looks big-bellied and
as if it were affected with a hernia, as I have
said. And now the colliquament, which was at
first in large quantity, gradually grows turbid,
suffers change, and is consumed, so that the
chick comes to lie bent over the vitellus. At
the same period, before the liver assumes its
sanguineous colour, and performs the business
of what is called the second concoction, the
bile, which is commonly believed to be sepa-
rated as an excretion by the power of the liver,
is seen of a green colour between the lobes of
that organ. In the cavity of the stomach there is
a limpid fluid contained, obviously of the same
appearance and taste as the colliquament in
which the foetus swims; this passing on by the
intestines, gradually changes its colour, and is
converted into chyle; and finally in the lower
portion of the bowels an excrementitious mat-
ter is encountered, of the same character as
that which is met with in the lower intestines
of chicks already excluded from the egg. When
the chick is further advanced you may even
see this fluid concocted and coagulated ; just as in
those animals that feed on milk, a coagulum is
formed, which afterwards separates into serum
and firmer curd.
When the albumen is almost all removed,
and only a very small quantity of the colliqua-
ment is left, for several days before the exclu-
sion, the chick no longer swims, but, as I have
said, bends over the vitellus; and rolled up into
a round ball, with the head for the most part
placed between the right thigh and wing, it is
seen with its beak, nails, feathers, and all other
parts complete. Sometimes it sleeps, and some-
times it wakes, and moving about it breathes
and chirps. If you apply the egg to your ear,
you will hear the chick within making a noise,
kicking, and unquestionably chirping; accord-
ing to Aristotle, he now also uses his eyes. If
you cautiously drop the egg into warm water,
it will swim, and the chick within, aroused by
the warmth, will leap, and, as I have already
said, cause the egg to tumble about. And it is by
this means that our country folks distinguish
prolific from unproductive eggs which sink
when put into water.
When the albumen is entirely gone, just be-
fore the exclusion, the umbilical vessel, which we
have described as distributed to the albumen,
is obliterated; or as Aristotle says, "that um-
bilicus which proceeds to the external secun-
dines is detached from the animal and dies; but
the one which leads to the vitellus becomes con-
nected with the small intestine of the chick."1
The excrement that is first formed in the in-
testines is white and turbid, like softened egg-
shell; and some of the same matter may be
found contained in the secundines. The philos-
opher admits this when he says: "At the same
time, too, the chick discharges a large quantity
of excrement into the outer membrane; and
there are white excrements within the abdo-
men, as well as those that have been evacuated."
Time running on, very shortly before the ex-
clusion, light green faeces are formed, similar to
those which the chick discharges when excluded
from the egg. In the crop, too, we can discover
a portion of the colliquament which has been
swallowed; and in the stomach some curd or
coagulum.
Up to this time the liver has not yet acquired
its purple or blood-red colour, but has a tint
verging from white into yellow, such as the
liver of fishes presents. The lungs, however, are
of a florid red.
The yelk is now contained in the abdomen
among the intestines: and this is the case not
merely whilst the chick is in the egg, but even
after its exclusion, and when it is running about
following its mother in search of food. So that
what Aristotle frequently asserts appears to be
absolutely true, viz., that the yelk is destined
for the food of the chick; and the chick does
certainly use it for food, included in his in-
terior as it is, during the few first days after his
exclusion, and until such time as his bill gains
the hardness requisite to break and prepare his
food, and his stomach the strength necessary to
digest it. And, indeed, the yelk of the egg is
very analogous to milk. Aristotle gives us his
support in this opinion in the place already so
frequently referred to: "The chick now lies
over much of the yellow, which at last dimin-
ishes, and, in process of time, disappears en-
tirely, being all taken into the body of the
bird, where it is stored, so that on the tenth
day after the exclusion of the chick, if the belly
be laid open, you will still find a little of the
yelk upon the intestines."2 1 have myself found
certain remains of the yelk even upon the thir-
teenth day; and if the argument derivable from
the duct of the umbilical veins which we have
described as terminating in the porta of the
liver by one or another trunk be of any avail,
the chick is already nourished almost in the
1 History of Animals, vi. 3.
ANIMAL GENERATION
same manner as it is subsequently, the sus-
tenance being attracted from the yelk by the
umbilical vessels, in the same way as chyle is by
and by transmitted by the mesenteric veins
from the intestines. For the vessels terminate in
either case in the porta of the liver, to which
the nourishment attracted in the same way is
in like manner transmitted. It is not necessary,
therefore, to have recourse to any lacteal ves-
sels of the mesentery, which, in the feathered
tribes, are nowhere to be distinguished.
Let me be permitted here to add what I have
frequently found: with a view to discovering
more distinctly the relative situations of the
embryo and the fluids, I have boiled an egg
hard, from the fourteenth day of the incuba-
tion up to the day when the exclusion would
have taken place, the major part of the albumen
being already consumed, and the vitellus divid-
ed. Breaking the shell, and regarding the posi-
tion of the chick, I found both the remains of
the albumen and the two portions of the vitellus
(which we have said are divided by the colli-
quation induced by the gentle heat) possessing
the consistency, colour, taste, and other quali-
ties which distinguish the yelks of unincubated
eggs similarly boiled. I have, therefore, fre-
quently asked myself how it came to pass that
unprolific eggs set under a hen are made to
putrefy and become offensive by the same ex-
traneous heat which produces no such effect
upon prolific eggs, both of the fluids of which re-
main sweet and unchanged, although they have
an embryo in the midst of them (and this even
containing some small quantity of excrementi-
tious matter within it), so that did any one eat
the yelk of such an egg in the dark, he would
not distinguish it from that of a fresh egg
which had never been sat upon.
EXERCISE 23. Of the exclusion of the chicly or the
birth from the egg
The egg is, as we have said, a kind of exposed
uterus, and place in which the embryo is
fashioned: for it performs the office of the
uterus and enfolds the chick until the due time
of its exclusion arrives, when the creature is
born perfect. Oviparous animals consequently
are not distinguished from viviparous by the
circumstance of the one bringing forth their
young alive, and the other not doing so; for the
chick not only lives and moves within the egg,
but even breathes and chirps whilst there; and,
when it escapes from the shell, enjoys a more
perfect existence than the foetus of animals in
general. Oviparous and viviparous animals ra-
ther differ in their modes of bringing forth; the
uterus or place in which the embryo is formed
being within the animal in viviparous tribes,
where it is cherished and brought to maturity,
whilst in oviparous tribes the uterus, or egg, is
exposed or without the animal, which, never-
theless, by sitting on it does not cherish it less
truly than if it were still contained within the
body.
For though the mother occasionally quits her
eggs on various errands, it is only for a short
season; she still has such affection for them that
she speedily returns, covers them over, cherish-
es them beneath her breast and carefully de-
fends them; and this on to the twenty-first or
twenty-second day, when the chicks, in search
of freer air, break the shell and emerge into the
light.
Now we must not overlook a mistake of
Fabricius, and almost every one else in regard
to this exclusion or birth of the chick. Let us
hear Fabricius.
"The chick wants air sooner than food, for it
has still some store of nourishment within it; in
which case the chick, by his chirping, gives a
sign to his mother of the necessity of breaking
the shell, which he himself cannot accomplish
by reason of the hardness of the shell and the
softness of his beak, to say nothing of the dis-
tance of the shell from the beak, and of the
position of the head under the wing. The chick,
nevertheless, is already so strong, and the cav-
ity in the egg is so ample, and the air contained
within it so abundant, that the breathing be-
comes free and the creature can emit the sounds
that are proper to it; these can be readily heard
by a bystander, and were recognized both by
Pliny and Aristotle,1 and perchance have some-
thing of the nature of a petition in their tone.
For the hen hearing the chirping of the chick
within, and knowing thereby the necessity of
now breaking the shell in order that the chick
may enjoy the air which has become needful to
it, or if you will, you may say, that desiring to
see her dear offspring, she breaks the shell with
her beak, which is not hard to do, for the part
over the hollow, long deprived of moisture, and
exposed to the heat of incubation, has become
dry and brittle. The chirping of the chick is
consequently the first and principal indication
of the creature desiring to make its escape, and
of its requiring air. This the hen perceives so
nicely, that if she hears the chirping to be low
and internal, she straightway turns the egg
over with her feet, that she may break the shell
1 Pliny, x. 53; Aristotle, History of Animals, vi. 3.
WILLIAM HARVEY
at the place whence the voice proceeds without
detriment to the chick."1 Hippocrates adds,
"Another indication or reason of the chick's
desiring to escape from the shell, is that when it
wants food it moves vigorously, in search of a
larger supply, by which the membrane around
it is torn, and the mother breaking the shell at
the place where she hears the chick moving
most lustily, permits it to escape."2
All this is stated pleasantly and well by Fab-
ricius; but there is nothing of solid reason in the
tale. For I have found by experience that it is
the chick himself and not the hen that breaks
open the shell, and this fact is every way in con-
formity with reason. For how else should the
eggs that are hatched in dunghills and ovens, as
in Egypt and other countries, be broken in due
season, where there is no mother present to at-
tend to the voice of the supplicating chick, and
to bring assistance to the petitioner? And how
again are the eggs of sea and land tortoises, of
fishes, silkworms, serpents, and even ostriches
to be chipped? The embryos in these have
either no voice with which they can notify
their desire for deliverance, or the eggs are
buried in the sand or slime where no chirping
or noise could be heard. The chick therefore is
born spontaneously, and makes its escape from
the eggshell through its own efforts. That this
is the case appears from unquestionable argu-
ments: when the shell is first chipped, the open-
ing is much smaller than accords with the beak
of the mother; but it corresponds exactly to
the size of the bill of the chick, and you may
always see the shell chipped at the same dis-
tance from the extremity of the egg, and the
broken pieces, especially those that yield to the
first blows, projecting regularly outwards in the
form of a circlet. But as anyone on looking at a
broken pane of glass can readily determine
whether the force came from without or from
within, by the direction of the fragments that
still adhere, so in the chipped egg it is easy to
perceive, by the projection of the pieces around
the entire circlet, that the breaking force comes
from within. And I myself and many others
with me besides, hearing the chick scraping
against the shell with its feet, have actually
seen it perforate this part with its beak, and ex-
tend the fracture in a circle like a coronet. I
have further seen the chick raise up the top of
the shell upon its head and remove it.
We have gone at length into some of these
matters, as thinking that they were not with-
1 Op. ctt., p. 59.
2 In the book DC nat. pueri.
out all speculative interest, as we shall show by
and by. The arguments of Fabricius are easily
answered. For I admit that the chick in ovo
produces sounds, and these perchance may even
have something of the implorative in their na-
ture; but it does not therefore follow that the
shell is broken by the mother. Neither is the
bill of the chick so soft, nor yet so far from the
shell, that it cannot pierce through its prison
walls, particularly when we see that the shell,
for the reasons assigned, is extremely brittle.
Neither does the chick always keep its head
under its wing, so as to be thereby prevented
from breaking the shell, but only when it sleeps
or has died. For the creature wakes at intervals
and scrapes and kicks, and struggles, pressing
against the shell, tearing the investing mem-
branes, and chirps (and that this is done whilst
petitioning for assistance 1 willingly concede),
all of which things may readily be heard by any
one who will use his ears. And the hen listening
attentively when she hears the chirping deep
within the egg does not break the shell, but
she turns the egg with her feet and gives the
chick within another and a more commodious
position. But there is no occasion to suppose
that the chick by his chirping informs his
mother of the propriety of breaking the shell,
or seeks deliverance from it. For very frequent-
ly for two days before the exclusion you may
hear the chick chirping within the shell.
Neither is the mother, when she turns the egg,
looking for the proper place to break it; but as
the child when uncomfortably laid in his cradle
is restless and whimpers and cries, and his fond
mother turns him this way and that, and rocks
him till he is composed again, so does the hen
when she hears the chick restless and chirping
within the egg, and feels it, when hatched,
moving uneasily about in the nest, immedi-
ately raise herself and observe that she is not
pressing on it with her weight, or keeping it too
warm, or the like, and then with her bill and
her feet she moves and turns the egg until the
chick within is again at its ease and quiet.
EXERCISE 24. Of twin- bearing eggs
Twin- bearing eggs are such as produce twin
chickens, and according to Aristotle, "are pos-
sessed of two yelks, which, in some are sepa-
rated by a layer of thin albumen, that they
may less encroach on one another; in others,
however, there is nothing of the sort, and then
the two yelks are in contact."3
I have frequently seen twin eggs, each of the
8 History of Animals, vi. 3.
ANIMAL GENERATION
383
yelks in which was surrounded by an albumen,
with common and proper membranes sur-
rounding them. I have also met with eggs hav-
ing two yelks connate, as it were, both of which
were embraced by a single and common albu-
men.
"Some fowls" says Aristotle,1 "always pro-
duce twins, in which the particulars relating to
the yelk that have been stated are clearly per-
ceived. A certain fowl laid within two of twen-
ty eggs, all of which, except those that were un-
prolific, produced twins. Of the twins, how-
ever, one was always larger, the other smaller,
and the smaller chick was frequently deformed
in addition."
With us twin eggs are occasionally produced,
and twin chicks too, although very rarely, are
engendered. I have never myself, however, seen
both of these chicks live and thrive; one of
them either died within the egg or at the time
of the exclusion. And this the words of Aristotle
prepare us to expect, when he says "one of the
two is larger, the other smaller"; this is as much
as to say that one of them is stronger and of
greater age, the other weaker and less prepared
for quitting the shell: my own opinion, there-
fore, is that the two yelks are of different ori-
gins and maturity. It is therefore scarcely pos-
sible but that the stronger and more advanced
chick, if the egg be broken and it emerge into
the light, will cause the blight and abortion of
the other. But if the stronger bird do not chip
the shell, he himself is threatened with a pres-
ent danger, viz., want of air. At the exclusion
from the shell, consequently, certain death
hangs over one or other, if not over both.
Fabricius, either not observing the above
words of Aristotle, or neglecting them, says:
"If an egg have now and then two yelks, it en-
genders a chick having four legs or wings, and
two heads— -a monster, in short; never two
chicks distinct from one another, and that can
be spoken of as a pair; there is but one trunk,
to which are appended two heads," &c.
Whence we may infer that he himself had
never seen nor heard from credible persons
that such eggs produce two pullets, and there-
fore that he agrees with me in regarding such
eggs as rare, and in holding that they never pro-
duce two chicks both alike capable of living.
I am surprised, nevertheless, that, with the
authority of Aristotle before him, he should
have said that "two chicks, distinct and sep-
arate, are never produced from such eggs," but
always a monster; the rather as he thinks that
the embryo is engendered from the chalazae as
from the appropriate matter, and he could not
but see that there are four chalazae in every
twin-egg.
I should rather imagine that when two vitelli
are included by the same albumen in a twin-
egg, and are so intimately associated that their
cicatriculae, when they are resolved together,
constitute a single eye or colliquament, may en-
gender a monstrous embryo with four feet, two
heads, &c., because I see nothing to hinder
this; and such a production do I conceive to
have been engendered by the egg of which
Fabricius speaks.
But where two yelks have existed separately,
parted by their several membranes, and fur-
nished with chalazae, albumens, and all else req-
uisite to the generation of the chick, I hold
that we must conclude, with Aristotle, that
such an egg, as it has all the parts of two eggs
except the shell, so does it also possess the facul-
ty or faculties of as many; and unless it be a
wind or barren egg, that it will for the most part
produce two embiyos, and but rarely a single
monstrous individual.
EXERCISE 25. Certain deductions from the
preceding history of the egg
Such is the history of the hen's egg; in which
we have spoken of its production, and of its
action or faculty to engender a chick, at too
great length, it may appear to those who do not
see the end and object of such painstaking, of
such careful observation. Wherefore I think it
advisable here to state what fruits may follow
our industry, and in the words of the learned
Lord Verulam, to "enter upon our second vin-
tage." Certain theorems, therefore, will have to
be gathered from the history given; some of
which will be quite certain, some questionable
and requiring further sifting, and some para-
doxical and opposed to popular persuasion.
Some of these, moreover, will have reference to
the male, some to the female, several to the
egg, and finally, a few to the formation of the
chick. When these have been carefully dis-
cussed seriatim, we shall be in a condition to
judge with greater certainty and facility of the
generation of all other animals.
EXERCISE 26. Of the nature of the egg
Of the theorems that refer to the egg, some
teach us what it is, some show its mode of for-
mation, and others tell of the parts which com-
pose it.
It is certain, in the first place, that one egg
WILLIAM HARVEY
produces one chick only. Although the egg be
in a certain sense an external uterus, still it
most rarely engenders several embryos, but by
far the most frequently produces no more than
a single pullet. And when an egg produces two
chicks, which it does sometimes, still is this egg
to be reputed not single but double, and as pos-
sessed of the nature and parts of two eggs.
For an egg is to be viewed as a conception
proceeding from the male and the female,
equally endued with the virtue of either, and
constituting an unity from which a single ani-
mal is engendered.
Nor is it the beginning only, but the fruit
and conclusion likewise. It is the beginning as
regards the being to be engendered; the fruit
in respect of the two parents: at once the end
proposed in their engendering, and the origin of
the chick that is to be. "But the seed and the
fruit," according to Aristotle,1 "differ from one
another in the relations of prior and posterior;
for the fruit is that which comes of another, the
seed is that from which this other comes: were
it otherwise, both would be the same."
The egg also seems to be a certain mean; not
merely in so far as it is beginning and end, but
as it is the common work of the two sexes and is
compounded by both; containing within itself
the matter and the plastic power, it has the
virtue of both, by which it produces a foetus
that resembles the one as well as the other. It is
further a mean between the animate and the in-
animate world; for neither is it wholly en-
dowed with life, nor is it entirely without vi-
tality. It is still further the mid-passage or tran-
sition stage between parents and offspring, be-
tween those who are, or were, and those who
are about to be; it is the hinge and pivot upon
which the whole generation of the bird re-
volves. The egg is the terminus from which all
fowls, male and female, have sprung, and to
which all their lives tend — it is the result
which nature has proposed to herself in their
being. And thus it comes that individuals in
procreating their like for the sake of their
species, endure for ever. The egg, I say, is a
period or portion of this eternity; for it were
hard to say whether an egg exists for the sake
of the chick that it engenders, or the pullet
exists for the sake of the egg which it is to en-
gender. Which of these was the prior, whether
with reference to time or nature — the egg or
the pullet? This question, when we come to
speak of the generation of animals in general,
we shall discuss at length.
1 On the Generation of Animals, i. 13*
The egg, moreover — and this is especially to
be noted — corresponds in its proportions with
the seeds of plants, and has all the same condi-
tions as these, so that it is to be regarded, not
without reason, as the seed or sperma of the
common fowl, in the same way as the seeds of
plants are justly entitled their eggs, not only
as being the matter or that from which, but the
efficient or that by which the pullet is engen-
dered. In which, finally, no part of the future
offspring exists de facto, but in which all parts
inhere in potentia.
The seed, properly so called, differs, how-
ever, from the geniture, which by Aristotle is
defined to be "that which, proceeding from the
generator, is the cause, that which first obtains
the principle of generation; in those, to wit,
whom nature destined to copulate. But the
seed is that which proceeds from these two in
their connexion: and such is the seed of all
vegetables, and of some animals, in which the
sexes are not distinct; like that which is first
produced by male and female commingled, a
kind of promiscuous conception, or animal;
for this already possesses what is required of
both."
The egg, consequently, is a natural body en-
dowed with animal virtues, viz., principles of
motion and rest, of transmutation and conser-
vation; it is, moreover, a body which, under
favorable circumstances, has the capacity to
pass into an animal form; heavy bodies indeed
do not sink more naturally, nor light ones
float, when they are unimpeded, than do seeds
and eggs in virtue of their inherent capacity
become changed into vegetables and animals.
So that the seed and the egg are alike the fruit
and final result of the things of which they are
the beginning and efficient cause.
For a single pullet there is a single egg; and
so Aristotle says: "from one seed one body is
engendered; for example, from a single grain of
wheat one plant; from a single egg one animal;
for a twin egg is, in fact, two eggs."2
And Fabricius with truth observes: "The
egg is not only an exposed uterus, and place of
generation, but that also on which the whole
reproduction of the pullet depends, and which
the egg achieves as agent, as matter, as instru-
ment, as seat, and all else, if more there be, that
is needful to generation."3 He shows it to be an
organ because it consists of several parts, and
this, from the statement of Galen, who will
have the very essence of an organ to be that "it
*/*«/., i. *>.
* Loc. cit.t p. 47.
ANIMAL GENERATION
385
consist of several parts, all of which conspire to
one and the same action though diverse in
faculty and use; for some are principal instru-
ments in the action; some are indispensable to
it— without them it could not take place; some
secure its better performance; and some, in
fine, are extant for the safety and preservation
of everything else." He also shows it to be an
agent, when from Aristotle and Galen he lays
down the two actions of the egg, viz. : "the gen-
eration of the chick, and the growth and nu-
trition of the pullet." At the conclusion he ex-
presses himself clearly in these words: "In the
works of nature we see conjunct and one, the
artificer, the instrument, and the matter; the
liver, for instance, is both the agent and the
instrument for the production of the blood;
and so every part of the body; Aristotle,1 there-
fore, said well that the moving powers were not
easily distinguished from the instruments. In
artificial things, indeed, the artificer and the
instrument are distinct, as much so as the
workman and his hammer, the painter and his
pencil. And the reason adduced by Galen2 is
this: that in things made by art the artificer is
without the work; in natural things, again, the
artificer is within it, conjunct with the in-
struments, and pervading the whole organi-
zation."
To this I add these perspicuous words of
Aristotle. "Of extant things some are consistent
with nature, others with other causes. Animals
and their parts, and plants, and simple bodies,
as earth, fire, air, and water, consist with na-
ture, and are allowed universally to do so; but
these bodies differ entirely from those that do
not consist with nature. For whatsoever con-
sists with nature is seen to have within itself a
principle of motion and of rest, now according
to place, now according to increment and de-
crement, and again according to change. A
couch or litter, a garment, and other things of
the same description, however designated, inas-
much as they are made by art, have no inherent
faculty of change; but inasmuch as they are
made of earth, or stone, or of mixtures of these,
they have such a faculty. As if nature were a
certain principle and cause wherefore that
should move and be at rest in which she in-
heres originally, independently, and not by
accident. I say, particularly, not by accident,
because it might happen that one being a phy-
sician should himself be the cause of his own
good health; but he is not familiar with medi-
1 On the Generation of Animals, u. 4.
2 Deform, foet.
cine in t^ie same respect as he has worked his
own cure; it happens simply that the man who
here recovers his health is a physician. It, there-
fore, occasionally happens that these two things
are distinct and separate. But it is not other-
wise with everything besides that is of art: none
of these has in itself a principle of performance
or action, though some of them have such a
principle in other things and beyond them-
selves, such as a house, and aught else that is
made with hands; and some have even such a
principle inherent, but not per se and inde-
pendently: everything, for example, may by
accident become a cause to itself. Nature is,
therefore, as stated; and those things have na-
ture within them which possess this principle.
Now all such are substances; for nature is al-
ways some subject, and inheres in the subject."3
These things I have spoken of at length, and
even quoted the words of the writers appealed
to, that it might thence appear first, that all I
attribute to the egg is actually there, viz. : mat-
ter, organ, efficient cause, place, and everything
else requisite to the generation of the chick;
and next and more especially, that the truth in
regard to the following very difficult questions
might be made clearly to appear, viz. : Which
and what principle is it whence motion and
generation proceed? By what virtue does the
semen act, according to Aristotle? What is it
that renders the semen itself fruitful ? (for the
philosopher will have it that nature in all nat-
ural bodies is the innate principle of motion
and of rest, and not any second accident).
Whether is that which in the egg is cause, arti-
ficer, and principle of generation and of all the
vital and vegetative operations — conservation,
nutrition, growth — innate or superadded ? And
whether does it inhere primarily, of itself, and
as a kind of nature, or intervene by accident, as
the physician in curing diseases? Whether is
that which transforms the egg into a pullet in-
herent or acquired, or is it already conceived in
the ovary, and does it nourish, augment, and
perfect the egg there ?
What is it besides that preserves the egg
sweet after it is laid ? What is it that renders an
egg fruitful— is it to be called soul, or a portion
of the soul, or something belonging to the soul,
or something having a soul, or is it intelli-
gence, or, finally, is it Divinity seeing that it
acts to a definite end, and orders all with inimi-
table providence and art, and yet in an incom-
prehensible manner, always obtaining what is
best both for simple being and for well-being,
8 Physics, u. i.
386
WILLIAM HARVEY
for protection also and for ornament ? And all
this not only in the fruitful egg which it fecun-
dates, but in the hypenemic egg which it
nourishes, causes to increase, and preserves.
Nay, it is not merely the vitellus in the vitel-
larium or egg-bed, but the smallest speck
whence the yelk is produced, of no greater size
than a millet or a mustard-seed, that it nour-
ishes and makes to grow, and finally envelopes
with albumen, and furnishes with chalazae, and
surrounds with membranes and a shell. For it is
probable that even the barren egg, whilst it is
included within the fowl and is connected with
her, is nourished and preserved by its internal
and inherent principle, and made to increase
(not otherwise than the eggs of fishes and frogs,
exposed externally, increase and are perfected),
and to be transformed from a small speck into a
yelk, and transferred from the ovary to the
uterus (though it have no connexion with the
uterus), there to be endued with albumen, and
at length to be completed with its chalazae,
membranes, and shell.
But what that may be in the hypenemic egg
as well as in the fruitful one, which in a similar
manner and from the same causes or principles
produces the same effects; whether it be the
same soul, or the same part of the soul, or some-
thing else inherent in both, must be worthy of
inquiry: it seems probable, however, that the
same things should proceed from similar causes.
Although the egg whilst it is being produced
is contained within the fowl, and is connected
with the ovary of the mother by a pedicle, and
is nourished by blood-vessels, it is not therefore
to be spoken of as a part of the mother; nor is it
to be held as living and vegetating through her
vital principle, but by a virtue peculiar to itself
and an internal principle; just as fungi, and
mosses, and the mistletoe, which although they
adhere to vegetables and are nourished by the
same sap as their leaves and germs, still form no
part of these vegetables, nor are they ever so
esteemed. Aristotle, with a view to meeting
these difficulties, concedes a vegetative soul to
the egg, even to the hypenemic one. He says:
"Females, too, and all things that live are en-
dowed with the vegetative virtue of the soul, as
has been often said; and therefore this egg is
perfect as the conception of a plant, but imper-
fect as that of an animal."1 And he inculcates
the same doctrine elsewhere, when he asks: "In
what manner or sense are hypenemic eggs said
to live ? For they cannot do so in the same sense
as fruitful eggs, otherwise a living thing might
1 On the Generation ofAnimals% in. 7.
be engendered by their agency. Nor do they
comport themselves like wood or stone; be-
cause these perish by a kind of corruption, as
having formerly had life in a certain manner.
It is positive, therefore, that hypenemic eggs
have a certain kind of soul potentially; but
what? of necessity that ultimate soul, which is
the appanage of vegetables; for this equally in-
heres in all things, in animals as well as vege-
tables."2
But it is not the same soul that is found in
hypenemic as in fruitful eggs; otherwise would
a pullet be indifferently produced from both;
but how and in what respects the soul attached
to each is different from the other, Aristotle
does not sufficiently explain, when he inquires:
"Wherefore are all the parts of an egg present in
the hypenemic egg, and it still incapable of pro-
ducing a chick? because," he replies, "it is req-
uisite that it have a sensitive soul."3 As if in
fruitful eggs, besides the vegetative soul, there
were a sensitive soul present. Unless you under-
stand the vegetative soul as inhering actually in
the fruitful egg, which contains the sensitive
soul within it potentially; whence the animal,
and the sensible parts of the animal are subse-
quently produced. But neither do writers sat-
isfactorily untie this knot, nor set the mind of
the inquirer free from the difficulties that en-
tangle him. For he sees that the egg is a true
animal seed, according to this sentence of the
Stagyrite: "In those things endowed with life,
in which the male and female sexes are not dis-
tinct, the seed is already present as a concep-
tion. I entitle conception the first mixture from
the male and female (the analogue of the vege-
table seed therefore). Wherefore from one seed
there is engendered one body, as from one egg
one animal."4
It appears, consequently, that for one egg
there is one soul or vital principle. But whether
is this that of the mother, or that of the father,
or a mixture ol the two? And here the greatest
difficulties are occasioned by those eggs that
are produced by the concurrence of animals of
different species, as, for example, of the com-
mon fowl and pheasant. In such an egg, I ask, is
it the vital principle of the father or that of the
mother, which inheres? or is it a mixture of
the two ? But how can vital principles be min-
gled, if the vital principle (as form) be act and
substance, which it is, according to Aristotle?
For no one will deny, whatever it be ultimately
8 Ibid., n. 4.
'/£«/., n. 4.
4 Ibid.) i. 20.
ANIMAL GENERATION
387
which in the fruitful egg is the beginning and
cause of the effects we witness, that it is a sub-
stance susceptible of divers powers, forces, or
faculties, and even conditions— virtues, vices,
health, and sickness. For some eggs are es-
teemed to be longer, others shorter lived; some
engender chickens endowed with the qualities
and health of body that distinguished their
parents, others produce young that are predis-
posed to disease. Nor is it to be said that this is
from any fault of the mother, seeing that the
diseases of the father or male parent are trans-
ferred to the progeny, although he contributes
nothing to the matter of the egg; the procrea-
tive or plastic force which renders the egg
fruitful alone proceeding from the male; none
of its parts being contributed by him. For the
semen which is emitted by the male during
intercourse does by no means enter the uterus
of the female, in which the egg is perfected; nor
can it, indeed (as I first announced, and Fab-
ncius agrees with me), by any manner or way
;et into the inner recesses of that organ, much
less ascend as high as the ovary, near the waist
or middle of the body, so that besides its pecul-
iar virtue it might impart a portion of matter
to the numerous ova whose rudiments are there
contained. For we know, and are assured by
unquestionable experience, that several ova are
fecundated by one and the same connexion —
not those only that are met with in the uterus
and ovary, but those likewise that are in some
sort not yet begun, as we shall state by and by,
and indeed, as we have already had occasion to
assert in our history.
If, therefore, an egg be rendered fruitful by
its proper vital principle, or be endowed with
its own inherent fecundating force, whence or
whereby either a common fowl, or a hybrid be-
twixt the fowl and the pheasant is produced, and
that either male or female, like the father or the
mother, healthy or diseased; we must infallibly
conclude that the egg, even when contained in
the ovary, does not live by the vital principle
of the mother, but is, like the youth who comes
of age, made independent even from its first
appearance; as the acorn taken from the oak,
and the seeds of plants in general, are no longer
to be considered parts of the tree or herb that
has supported them, but things made in their
own right, and which already enjoy life in vir-
tue of a proper and inherent vegetative power.
But if we now admit that there is a living
principle in a fertile egg, it may become matter
of discussion whether it is the same living prin-
ciple which already inheres in the egg that will
inhere in the future chick, or whether it is a
different one that actuates each ? For it is matter
of necessity that we admit the inherence of a cer-
tain principle which constitutes and causes the
egg to grow, and which further engenders and
makes the chick to increase. We have to in-
quire, therefore, whether the animating prin-
ciple of the egg and of the chick be one and the
same, or several and different ? And then, were
several vital principles recognized, some apper-
taining to the egg, others to the chick, we
should next have to inquire: whence and at
what epoch the animating principle of the
chick entered it ? and what is it in the egg which
causes the cicatricula to dilate before the ad-
vent of the living principle; which draws the
eye of the vitellus upwards, as stated, and pro-
duces the colliquament, changes the constitu-
tion of the fluids of the egg, and preordains
everything for the construction of the future
chick before there is even a vestige of it to be
seen? Or whence shall we say the aliment fit
for the embryo is derived, and by which it is
nourished and made to grow, before it is yet in
being? For these acts are seen to be the work
of the vegetative soul of the embryo, and have
reference to the coming pullet, ensuring its
nutrition and growth. And again, when the em-
bryo is begun, or the chick is half formed, what
is it which constitutes that embryo or that
chick one and continuous and connects with the
liquids of the egg ? What nourishes and makes
the chick to grow, and preserves the fluids that
are fit for its nutrition from putrefaction, and
prepares, and liquefies, and concocts them?
If the vital principle be the act of the organic
body possessing life inpotentia, it seems incredi-
ble that this principle can inhere in the chick
before something in the shape of an organized
body is extant. Nor is it more credible that the
vital principle of the egg and chick can be iden-
tical, if the vital principle be conservative of
that only to which it belongs; but the egg and
the chick are different things, and manifest dis-
similar and even opposite vital acts, in so much
so that one appears to be produced by the de-
struction of the other. Or should we perchance
maintain that the same principle and cause of
life inheres in both, in the pullet half fashioned,
to wit, and the egg half consumed, as if it were
one and a simple act of the same body ; or as if
from parts producing one natural body, one
soul or vital principle also arose, which was all
in all, as is commonly said, and all in each par-
ticular part ? Just as with leaves and fruit con-
spicuous on the stem of a tree, wherever a divi-
388
WILLIAM HARVEY
sion is made we still say that the principle or
first cause of the slip and of the whole tree is
the same; the leaves and the fruit are, as it were,
the form and end, the trunk of the tree the be-
ginning. So too in a line, wherever a division is
made, this will become the end or boundary of
the part behind it, the commencement of the
part before it. And the same thing is seen to ob-
tain in respect of quality and motion, that is to
say, in every kind of transmutation and gener-
ation.
So much at this time upon these topics,
which will by and by engage us at greater
length, when we come to speak of the nature
of the living principle of the embryos of ani-
mals in general; of its being; of its accession in
respect of the how and the when; and how it is
all in all, and all in each particular part, the
same and yet different. Points which we shall
determine from numerous observations.
EXERCISE 27. The egg is not the product of the
uterus > but of the vital principle
"As we have said," says Fabricius,1 "that the
action of the stomach was to convert the food
into chyle, and the action of the testicles to pro-
duce semen, because in the stomach we find
chyle, in the testes semen, so do we definitely
assert that the egg is the product of the uterus
of birds, because it is found in this part. The
organ and seat of the generation of eggs is,
therefore, intimately known and obvious to us.
And further, inasmuch as there are two uteri in
birds, one superior and the other inferior, and
these are considerably different from one an-
other, and consequently perform different of-
fices, it is in like manner clear what particular
action is to be ascribed to each. The superior is
devoted to the production of the yelk, the infe-
rior to that of the albumen and remaining
parts, or of the perfect egg, as lies obvious to
sense; for in the superior uterus we never find
aught beyond a multitude of yelks, nor in the
inferior uterus, other than entire and perfect
eggs. But these are not all the functions of the
uteri as it appears, but the following are further
to be noted and enumerated, viz. : the increase
of the egg, which succeeds immediately upon
its production, and proceeds until it is per-
fected and acquires its proper dimensions. For
the fowl does not naturally lay an egg until it
has become complete and has acquired its due
dimensions. The actions of the uteri are conse-
quently the increase as well as the engender-
ment of the egg; but increase supposes and in-
1 Of. cit., p. 8,
eludes nutrition, as is obvious. And since all
generation Is the effect of the concurrence of
two, viz., the agent and the matter, the agent
in the generation of an egg is nothing else than
the instruments or organs aforesaid, to wit, the
double uterus; and the matter is nothing but
the blood."
Now whilst I admit the action of the uterus
to be in a manner the generation of the egg, I
by no means allow that the egg is nourished
and increased by this organ. And this, both for
the reasons already alleged by us when we
treated of the vital principle of the egg, which
is that which nourishes it, and also because it
appears little likely (according to Aristotle,2 it
is impossible) that all the internal parts of the
egg, in all their dimensions, should be fashioned
and made to increase by an external agent, such
as the uterus is with reference to the egg; for
how, I beseech you, can that which is extrinsic
arrange the natural matter in things that are
internal, and supply fresh matter according to
the several dimensions in the place of that
which has been lost? How can anything be af-
fected or moved by that which does not touch
it? Wherefore, without question, the same
things happen in the engenderment of eggs
which take place in the beginning of all living
things whatsoever, viz.: they are primarily
constituted by external and pre-existing beings;
but so soon as they are endowed with life, they
suffice for their own nourishment and increase,
and this in virtue of peculiar inherent forces,
innate, implanted from the beginning.
What has already been said of the vital prin-
ciple appears clearly to proclaim that the egg is
neither the work of the uterus, nor governed by
that organ; for it is manifest that the vegeta-
tive principle inheres even in the hypenemic
egg, inasmuch as we have seen that this egg is
nourished and is preserved, increases and vege-
tates, all of which acts are indications of the
presence of the principle mentioned. But
neither from the mother nor the uterus can this
principle proceed, seeing that the egg has no
connexion or union with them, but is free and
unconnected, like a son emancipated from pu-
pillage, rolling round within the cavity of the
uterus and perfecting itself, even as the seeds of
plants are perfected in the bosom of the earth,
viz.y by an internal vegetative principle, which
can be nothing else than the vegetative soul.
And it will appear all the more certain that it
is possessed of a soul or vital principle, if we
consider by what compact, what moving power,
* On the Generation of Animals, 11. i.
ANIMAL GENERATION
389
the round and ample yelk, detached from the
cluster of the ovary, descends through the in-
fundibulum — a most slender tube composed of
a singularly delicate membrane, and possessed
of no motory fibres — and opening a path for
itself, approaches the uterus through such a
number of straits, arrived in which it contin-
ues to be nourished, and grows and is sur-
rounded with albumen. Now as there is no
motory organ discoverable either in the ovary
which expels the vitellus, or in the infundibu-
lum which transmits, or in the uterus which
attracts it, and as the egg is not connected with
the uterus, nor yet with the ovary by means of
vessels, nor hangs from either by an umbili-
cal cord, as Fabricius truly states, and demon-
strates most satisfactorily, what remains for us
contemplating such great and important pro-
cesses but that we exclaim with the poet:
'Tis innate soul sustains; and mind infused
Through every part, that actuates the mass.1
And although the rudiments of eggs, which we
have said are mere specks, and have compared
to millet seeds in size, are connected with the
ovary by means of veins and arteries, in the
same manner as seeds are attached to plants,
and consequently seem to be part and parcel
of the fowl, and to live and be nourished after
the manner of her other parts, it is nevertheless
manifest, that seeds once separated from the
plants which have produced them, are no
longer regarded as parts of these, but like chil-
dren come of age and freed from leading-strings,
they are maintained and governed by their own
inherent capacities.
But of this matter we shall speak more fully,
when we come to treat of the soul or living
principle of the embryo in general, and of the
excellence and divine nature of the vegetative
soul from a survey of its operations, all of which
are carried on with such foresight, art, and
divine intelligence; which, indeed, surpass our
powers of understanding not less than Deity
surpasses man, and are allowed, by common
consent, to be so wonderful that their ineffable
lustre is in no way to be penetrated by the dull
edge of our apprehension.
What shall we say of the animalcules which
are engendered in our bodies, and which no
one doubts are ruled and made to vegetate by a
peculiar vital principle (anima) ? of this kind
are lumbrici, ascarides, lice, nits, syrones, acari,
&c. ; or what of the worms which are produced
from plants and their fruits, as from gall-nuts,
lVirgil, &ncid, vi.
the dog-rose, and various others? 'Tor in al-
most all dry things growing moist, or moist
things becoming dry, an animal may be en-
gendered/*2 It certainly cannot be that the liv-
ing principles of the animals which arise in gall-
nuts existed in the oak, although these animals
live attached to the oak, and derive their sus-
tenance from its juices. In like manner it is
credible that the rudiments of eggs exist in the
ovarian cluster by their proper vital principle,
not by that of the mother, although they are
connected with her body by means of arteries
and veins, and are nourished by the same food
as herself. Because, as we have stated in our his-
tory, all the vitellary specks do not increase to-
gether, like the grapes of a bunch, or the corns
of an ear of wheat, as if they were pervaded by
one common actuating force or concocting and
forming cause; they come on one after another,
as if they grew by their own peculiar energy,
each that is most in advance severing itself from
the rest, changing its colour and consistence,
and from a white speck becoming a yelk, in reg-
ular and determinate sequence. And what is
more particularly astonishing is that which we
witness among pigeons and certain other birds,
where two yelks only come to maturity upon
the ovarian cluster together, one of which, for
the major part, produces a male, the other a fe-
male, an abundance of other vitellary specks
remaining stationary in the ovary, until the
term comes round for two more to increase and
make ready for a new birth. It is as if each suc-
cessive pair received fertility from the repeated
addresses of the male; as if the two became pos-
sessed of the vital principle together; which,
once infused, they forthwith increase spontan-
eously, and govern themselves, living of their
own not through their mother's right. And, in
sooth, what else can you conceive working, dis-
posing, selecting, and perfecting, as respects
this pair of vitellary papulae and none others,
but a peculiar vital principle? And although
they attract nourishment from the mother,
they still do so no otherwise than as plants
draw food from the ground, or as the embryo
obtains it from the albumen and vitellus.
Lastly, since the papula existing in the ovary
receives fecundity from the access of the male,
and this of such a kind that it passes into the
form and likeness of the concurring male,
whether he were a common cock or a pheasant,
and there is as great diversity in the papulae as
there are males of different kinds; what shall
we hold as inherent in the papulae themselves,
2 Aristotle, History of Animals y v. 32.
390
WILLIAM HARVEY
by whose virtue they are distinguished from
one another and from the mother? Undoubted-
ly it must be the vital principle by which they
are distinguished both from each other and
from the mother.
It is in a similar manner that fungi and para-
sitic plants live upon trees. And besides, we in
our own bodies frequently suffer from cancers,
sarcoses, melicerides, and other tumours of the
same description, which are nourished and grow
as it seems by their own inherent vegetative
principle, the true or natural parts of the body
meantime shrinking and perishing. And this ap-
parently because these tumours attract all the
nourishment to themselves, and defraud the
other parts of the body of their nutritious
juices- or proper genius. Whence the familiar
names of phagedaena and lupus; and Hippo-
crates, by the words TO Otlov, perhaps under-
stood those diseases which arise from poison or
contagion; as if in these there was a certain vi-
tality and divine principle inherent, by which
they increase and through contagion generate
similar diseases even in other bodies. Aristotle,
therefore, says: "all things are full of soul";1
and elsewhere he seems to think that "even the
winds have a kind of life, and a birth and a
death."2 But there is no doubt that the vitellus,
when it is once cast loose and freed from all
connexion with the fowl, during its passage
through the infundibulum and its stay in the
cavity of the uterus, attracts a sluggish mois-
ture to itself, which it absorbs, and by which it
is nourished; there too it surrounds itself with
albumen, furnishes itself with membranes and
a shell, and finally perfects itself. All of which
things, rightly weighed, we must needs con-
clude that it is possessed by a proper vital prin-
ciple (anima).
EXERCISE 28. The egg is not produced without the
hen
Leaving points that are doubtful, and dis-
quisitions bearing upon the general question,
we now approach more definite and obvious
matters.
And first, it is manifest that a fruitful egg
cannot be produced without the concurrence
of a cock and hen: without the hen no egg can
be formed; without the cock it cannot become
fruitful. But this view is opposed to the opinion
of those who derive the origin of animals from
the slime of the ground. And truly when we see
that the numerous parts concurring in the act
1 On the Generation of Animals t nz. 2.
2 lbtd.> iv. 10.
of generation — the testes and vasa deferentia in
the male, the ovarium and uterus and blood-
vessels supplying them in the female — are all
contrived with such signal art and forethought,
and everything requisite to reproduction in a
determinate direction— situation, form, tem-
perature— arranged so admirably, it seems cer-
tain, as Nature does nothing in vain, nor works
in any round-about way when a shorter path
lies open to her, that an egg can be produced in
no other manner than that in which we now see
it engendered, vtz., by the concurring act
of the cock and hen. Neither, in like manner, in
the present constitution of things, can a cock or
hen ever be produced otherwise than from an
egg. Thus the cock and the hen exist for the
sake of the egg, and the egg, in the same way, is
their antecedent cause; it were therefore reason-
able to ask, with Plutarch, which of these was
the prior, the egg or the fowl ? Now the fowl is
prior by nature, but the egg is prior in time;
for that which is the more excellent is naturally
first; but that from which a certain thing is
produced must be reputed first in respect of
time. Or we may say: this egg is older than that
fowl (the fowl having been produced from it) ;
and, on the contrary, this fowl existed before
that egg (which she has laid). And this is the
round that makes the race of the common fowl
eternal; now pullet, now egg, the series is con-
tinued in perpetuity ; from frail and perishing in-
dividuals an immortal species is engendered.
By these, and means like to these, do we see
many inferior or terrestrial things brought to
emulate the perpetuity of superior or celestial
things.
And whether we say, or do not say, that the
vital principle (anima) inheres in the egg, it still
plainly appears, from the circuit indicated,
that there must be some principle influencing
this revolution from the fowl to the egg and
from the egg back to the fowl, which gives them
perpetuity. Now this, according to Aristotle's
views,3 is analogous to the element of the stars;
and is that which makes parents engender, and
gives fertility to their ova; and the same prin-
ciple, Proteus-like, is present under a different
form, in the parents as in the eggs. For, as the
same intelligence or spirit which incessantly ac-
tuates the mighty mass of the universe, and
compels the same sun from the rising to the
setting, in his passage over the various regions
of the earth, so also is there a vis enthea, a di-
vine principle inherent in our common poultry,
showing itself now as the plastic, now as the
»/£&/., ix. 3.
ANIMAL GENERATION
39'
nutritive, and now as the augmentative force,
though it is always and at all times present as
the conservative and vegetative force, and now
assumes the form of the fowl, now that of the
egg; but the same virtue continues to inhere in
either to eternity. And although some animals
arise spontaneously, or as is commonly said from
putrefaction, and some are produced from the
female alone, for Pliny says: "in some genera,
as in certain fishes, there are no males, every one
taken being found full of roe";1 still whatever
is produced from a perfect egg is so in virtue of
the indispensable concurrence of male and fe-
male. Aristotle consequently says: "the grand
principles of generation must be held to be the
male and the female";2 the first two principles
of the egg are therefore the male and the fe-
male; and the common point or conception
of these is the egg, which combines the virtues of
both parents. We cannot, in fact, conceive an
egg without the concurrence of a male and fe-
male fowl, any more than we can conceive fruit
to be produced without a tree. We therefore
see individuals, males as well as females, existing
for the sake of preparing eggs, that the species
may be perennial, though their authors pass
away. And it is indeed obvious that the parents
are no longer youthful, or beautiful, or lusty,
and fitted to enjoy life, than whilst they possess
the power of producing and fecundating eggs,
and, by the medium of these, of engendering
their like. But when they have accomplished
this grand purpose of nature, they have already
attained to the height, the awy of their being
— the final end of their existence has been ac-
complished; after this, effete and useless, they
begin to wither, and, as if cast off and forsaken
of nature and the Deity, they grow old, and,
a- weary of their lives, they hasten to their end.
How different the males when they make them-
selves up for intercourse, and swelling with de-
sire are excited by the venereal impulse! It is
surprising to see with what passion they are in-
flamed; and then how trimly they are feathered,
how vainglorious they show themselves, how
proud of their strength, and how pugnacious
they prove! But, the grand business of life ac-
complished, how suddenly, with failing strength
and pristine fervour quenched, do they take in
their swelling sails, and, from late pugnacity,
grow timid and desponding! Even during the
season of jocund masking in Venus' domains,
male animals in general are depressed by inter-
course, and become submissive and pusillani-
1 Hist, natur., ix. 16.
* On the Generation of Animals, i. 2.
mous, as if reminded that in imparting life to
others, they were contributing to their own de-
struction. The cock alone, replete with spirit
and fecundity, still shows himself alert and gay;
clapping his wings, and crowing triumphantly,
he sings the nuptial song at each of his new
espousals! yet even he, after some length of
time in Venus' service, begins to fail; like the
veteran soldier, he by and by craves discharge
from active duty. And the hen, too, like the
tree that is past bearing, becomes effete, and is
finally exhausted.
EXERCISE 29. Of the manner, according to Aris-
totle, in which a perfect and fruitful egg is produced
by the male and female fowl
Shortly before we said that a fruitful egg is
not engendered spontaneously, that it is not
produced save by a hen, and by her only
through the concurrence of the cock. This
agrees with the matter of the following sen-
tence of Aristotle: "The principles of generation
have particular reference to male and female;
the male as supplying the original of motion
and reproduction; the female as furnishing the
matter."3
In our view, however, an egg is a true genera-
tive seed, analogous to the seed of a plant; the
original conception arising between the two
parents, and being the mixed fruit or product
of both. For as the egg is not formed without
the hen, so is it not made fruitful without the
concurrence of the cock.
We have, therefore, to inquire how the egg is
produced by the hen and is fertilized by the
cock; for we have seen that hypenemic eggs,
and these animated too, are engendered by
the hen, but that they are not prolific with-
out the intercourse of the cock. The male and
the female consequently, both set their mark
upon a fruitful egg; but not, I believe, in the
way in which Aristotle imagines, viz. : that the
male concurs in the motion and commencement
of generation only, the female supplying noth-
ing but the matter, because the contrary of
this is obvious in hypenemic eggs. And al-
though it be true as he says: "That male and
female differ in respect of reason, because the
faculty of each is different, and in respect of
sense, because certain parts differ likewise. The
difference according to reason boasts this dis-
tinction, that the male has the power of en-
gendering in another; the female has only the
power of engendering in herself; whereby it
comes that that which is engendered is pro-
8 Ibid., I. 2.
39*
WILLIAM HARVEY
duced, this being contained in that which en-
genders. But as males and females are dis-
tinguished by certain faculties and functions,
and as an instrument is indispensable to every
office, and the parts of the body are adapted as
instruments of the functions, it was necessary
that certain parts should be set aside for pur-
poses of procreation and coition, and these dif-
fering from one another, whereby the male
differs from the female."
It does not, however, follow from thence,
that what he appears inclined to infer is cor-
rect, where he says: "The male is the efficient
agent, and by the motion of his generative vir-
tue (genitura), creates what is intended from the
matter contained in the female; for the female
always supplies the matter, the male the power
of creation, and this it is which constitutes one
male, another female. The body and the bulk,
therefore, are necessarily supplied by the fe-
male; nothing of the kind is required from the
male; for it is not even requisite that the instru-
ment, nor the efficient agent itself, be present
in the thing that is produced. The body, then,
proceeds from the female, the vital principle
(animd) from the male; for the essence of every
body is its vital principle (animd)'' But an
egg, and that animated, is engendered by the
pullet without the concurrence of the male;
whence it appears that the hen too, or the fe-
male, may be the efficient agent, and that all
creative force or vital power (animd) is not de-
rived exclusively from the male. This view in-
deed appears to be supported by the instance
quoted by Aristotle himself, for he says:
"Those animals not of the same species, which
copulate (which those animals do that corre-
spond in their seasons of heat and times of
uterogestation, and do not differ greatly in
their size), produce their first young like them-
selves, but partaking of the species of both par-
ents; of this description is the progeny of the
fox and dog, of the partridge and common
fowl, &c. ; but in the course of time from diver-
sity results diversity, and the progeny of these
different parents at length acquires the form of
the female; in the same way as foreign seed is
changed at last in conformity with the nature
of the soil, which supplies matter and body to
the seed."1
From this it appears, that in the generation
of the partridge with the common fowl it is not
the male alone that is efficient, but the female
also; inasmuch as it is not the male form only,
but one common or subordinate that appears in
1 Op.
t n. 4.
the hybrid, as like the female as it is like the
male in vital endowment (animd)) and bodily
form. But the vital endowment (animd) is that
which is the true form and species of an animal.
Further, the female seems even to have a
superior claim to be considered the efficient
cause: "In the course of time," says the philos-
opher, "the progeny of different species as-
sumes the form of the female" as if the semen
or influence of the male were the less powerful ; as
if the species impressed by him disappeared
with the lapse of time, and were expelled by a
more powerful efficient cause. And the in-
stance from the soil confirms this still further:
"for foreign seeds are changed at length ac-
cording to the nature of the soil." Whence it
seems probable that the female is actually of
more moment in generation than the male; for,
"in the world at large it is admitted that the
earth is to nature as the female or mother,
whilst climate, the sun, and other things of the
same description, are spoken of by the names of
generator and father."2 The earth, too, spon-
taneously engenders many things without seed;
and among animals, certain females, but fe-
males only, procreate of themselves and with-
out the concurrence of the male: hens, for ex-
ample, lay hypenemic eggs; but males, without
the intervention of females, engender nothing.
By the same arguments, indeed, by which
the male is maintained to be the principle and
prime efficient in generation, it would seem
that the female might be confirmed in the pre-
rogative of Ivepydq. or efficiency. For is not
that to be accounted efficient in which the rea-
son of the embryo and the form of the work ap-
pear; whose obvious resemblance is perceived
in the embryo, and which, as first existing, calls
forth the other? Since, therefore, the form,
cause, and similitude inhere in the female not
less — and it might even be said that they inhere
more— than in the male, and as she also exists
previously as prime mover, let us conclude for
certain that the female is equally efficient in
the work of generation as the male.
And although Aristotle says well and truly,
"that the conception or egg receives no part of
its body from the male, but only its form, spe-
cies, and vital endowment (animd) , and from
the female its body solely, and its dimensions,"3
it is not yet made sufficiently to appear that
the female, besides the matter, does not in some
measure contribute form, species, and vital en-
dowment (animd). This indeed is obvious in
8 Op. cit.j i. 2,
8 Op. «/., n. 4.
ANIMAL GENERATION
393
the hen which engenders eggs without the con-
currence of a male; in the same way as trees
and herbs, in which there is no distinction of
sexes, produce their seeds. For Aristotle him-
self admits1 that even the hypenemic egg is
endowed with a vital principle (anima). The fe-
male must therefore be esteemed the efficient
cause of the egg.
Admitting that the hypenemic egg is pos-
sessed of a certain vital principle, still it is not
prolific; so that it must further be confessed
that the hen of herself is not the efficient cause
of a perfect egg, but that she is made so in vir-
tue of an authority, if I may use the word, or
power required of the cock. For the egg, unless
prolific, can with no kind of propriety be ac-
counted perfect; it only obtains perfection
from the male, or rather from the female, as it
were, upon precept from the male; as if the hen
received the art and reason, the form and laws
of the future embryo from his address. And so
in like manner the female fowl, like to a fruitful
tree, is made fertile by coition; by this is she
empowered not only to lay eggs, but these per-
fect and prolific eggs. For although the hen
have as yet no rudiments of eggs prepared in
her ovary, nevertheless, made fertile by the in-
tercourse of the male, she by and by not only
produces them there, but lays them, teeming
with life, and apt to produce embryos. And
here that practice of the poor folks finds its ap-
plication: "Having hens at home, but no cock,
they commit their females to a neighbour's
male for a day or two; and from this short so-
journ the fecundity of the whole of the eggs
that will be laid during the current season is se-
cured."2 Not only are those eggs which are still
nothing more than yelk and have no albumen,
or which exist only as most minute specks in
the ovary, but eggs not yet extant, that will be
conceived long afterwards, rendered fertile by
the same property.
EXERCISE 30. Of the uses of this disquisition on
fecundity
This disquisition on the inherent qualities of
the egg and the cause of its fecundity, is alike in
point of difficulty and subtlety, but of the
highest importance. For it was imperative on us
to inquire what there was in the conception,
what in the semen masculinum, and what in
the female fowl, which renders these fertile;
and what there is in the fruitful cock which
makes him differ from a bird that is barren. Is
1 Op. a/., ii. 4.
2 Fabncius, op. cit.t p. 37.
the cause identical with that which we have
called the vital principle (ammo) in the em-
bryo, or is it a certain portion of the vegetative
principle ? Because, in order to apprehend the
entire cause of generation, it is of much moment
that the first cause be understood; for science is
based upon causes, especially first causes,
known. Nor is this inquiry less important in en-
abling us to understand the nature of the vital
principle (anima). These questions, indeed,
rightly apprehended, not only are Aristotle's
opinions of the causes of generation refuted or
corrected, but all that has been written against
him is easily understood.
We ask, therefore, whether it is the same
thing or something different, which in the rudi-
mentary ovum, yelk, egg, cock and hen, or her
uterus, confers fruitfulness ? In like manner in
what respect does this something agree or dif-
fer in each? Still further, is it a substance
whence the fecundating virtue flows? — it ap-
pears susceptible of powers, faculties, and acci-
dents. Likewise, is it corporeal also? for that
which engenders mixture appears to be mixed
— the progeny has a common resemblance to
the mother and father, and exhibits a doubtful
nature when animals of dissimilar species, such
as the pheasant and common fowl, engender";
that, too, appears to be corporeal which suffers
from without, and to such an extent that not
only are weakly embryos procreated, but even
deformed and diseased ones, obnoxious to the
vices as well as to the virtues of their progeni-
tors.
With respect to these several particulars, we
may further be permitted to doubt whether
that which confers fecundity is engendered or
accrues from without. Whether, to wit, it is
transfused from the egg to the embryo and
chick, from the hen to the egg, from the cock
to the hen. For there appears to be something
that is transferred or transfused, something,
namely, which from the cock is transfused into
the hen, and from her is given to the uterus, to
the ovary, to the egg; something which, pass-
ing from the seed to the plant, is rendered
again by the plant to the seed, and imparts fe-
cundity. Because there is this common to all
things which are perpetuated by generation,
that they derive their origin from seed. But the
semen, the conception, and the egg, are all of
the same essential kind, and that which confers
fertility on these is one and the same, or of like
nature; and this indeed is divine, the analogue
of heaven, possessed of art, intelligence, fore-
sight. This is plainly to be seen from its admira-
394
WILLIAM HARVEY
blc operations, artifices, and wisdom, where
nothing is vain, or inconsiderate, or accidental,
but all conduces to some good end.
Of the general principles and science of this
subject we shall treat more at length in the
proper place; we have now said as much inci-
dentally as seems necessary, the occasion hav-
ing presented itself along with our considera-
tion of the hen's egg, namely, how many things
inhere which induce fertility, and how this is
indufced, and whether it is an affection, a habit,
a power, or a faculty; whether it is to be re-
garded as a form and substance, as a something
contained generally, or only in some particular
part— since it is quite certain that a hypenemic
egg is a perfect egg in so far as each sensible
particular is concerned, and yet is barren; the
uterus in like manner, and the hen and the
cock are all perfect; yet are they severally ster-
ile, as being without that which confers fecun-
dity. All of these matters we shall advert to after
we have shown what and how two principles,
male and female, concur in the production of
the egg and the process of generation, and in
what way both may be regarded as efficient
causes and parents of the egg.
EXERCISE 3 1 . The egg is not produced by the coc{
and hen in the way Aristotle would have it.
It is certain, as we have said, that a fruitful
egg is not produced without the concurrence of
the cock and hen; but this is not done in the
way that Aristotle thought, viz., by the cock as
prime and sole "agent," the hen only furnish-
ing the "matter." Neither do I agree with him
when he says: "When the semen masculinum
enters the female uterus, it coagulates the pur-
est portion of the catamenia"; and shortly
afterwards: "but when the catamenia of the
female has set in the uterus, it forms, with the
semen masculinum, a coagulum like that of
milk; for curd is milk containing vital heat,
which attracts like particles around it, and
combines and coagulates them; and the semen
of the male (geniturd) bears the same affinity to
the nature of the catamenia. For milk and the
menstrual discharge are of the same nature.
When coagulation has taken place, then an
earthy humour is excreted and is drawn around,
and the earthy portion drying up, the mem-
branes are produced both as matter of neces-
sity, and also for a certain purpose. And these
things take place in the same manner in all
creatures, both oviparous and viviparous."1
But the business in the generation of an egg
1 On the Generation of Animals, n. 4.
is very different from this; for neither does the
semen, or rather the "geniture," proceeding
from the male in the act of intercourse, enter
the uterus in any way, nor has the hen, after
she conceives, any particle of excrementitious
matter, even of the purest kind, or any blood
in her uterus which might be fashioned or per-
fected by the discharge of the male. Neither
are the parts of the egg, the membranes, to wit,
and the fluids, produced by any kind of coagu-
lation; neither is there anything like curdled
milk to be discovered in the uterus, as must be
obvious from the foregoing exercises. It follows,
therefore, and from thence, that neither does
the conception, whence the animal springs, as
the herb arises from a fruitful seed, comport
itself in the manner Aristotle imagined, since
this takes place in viviparous animals in the
same way as the egg is formed in oviparous ani-
mals, as he himself avows, and as shall be dem-
onstrated by and by in our observations. Be-
cause it is certain that eggs of every descrip-
tion—prolific and barren— are engendered and
formed by the hen singly, but that fecundity
accrues from the male alone; the cock, I say,
contributes neither form nor matter to the egg,
but that only by which it becomes fertile and
fit to engender a chick. And this faculty the
cock confers by his semen (geniturd), emitted
in the act of intercourse, not only on the egg
that is already begun, or is already formed, but
on the uterus and ovary, and even on the body
of the fowl herself, in such wise that eggs which
have yet to be produced, eggs, none of the mat-
ter of which yet exists either in the ovary or in
any other part of the body, are thence pro-
duced possessed of fecundity.
EXERCISE 32. Nor in the manner imagined by
physicians
Conception, according to the opinion of
medical men, takes place in the following way:
during intercourse the male and female dissolve
in one voluptuous sensation, and eject their
seminal fluids (geniturx) into the cavity of the
uterus, where that which each contributes is
mingled with that which the other supplies,
the mixture having from both equally the fac-
ulty of action and the force of matter; and ac-
cording to the predominance of this or of that
geniture does the progeny turn out male or fe-
male. It is further imagined that immediately
after the intercourse, the active and passive
principles cooperating, something of the con-
ception is formed in the uterus. For contrary
to the Aristotelians, they maintain that the
ANIMAL GENERATION
395
male is no more the efficient cause of generation
than the female, but some mixture of the two;
and that neither the menstrual blood nor its
purest part is the prime matter of the concep-
tion, but the spermatic fluid; whence the first
particles or their rudiments are spoken of as
spermatic, these at an after period being nour-
ished and made to increase through the blood.
But it is obvious that neither is the egg en-
gendered by the cock and hen in this way; for
the hen in the act of intercourse emits no semen
from which an egg might be formed; nor can
aught like a seminal fluid of the hen be demon-
strated at any time; and indeed the animal is
destitute of the organs essential to its prepara-
tion, the testes and vasa spermatica. And
though the hen have an effective force in com-
mon with the cock (as must be manifest from
what precedes), and it is a mixture of some sort
that renders an egg fruitful, still this does not
happen according to the predominance of the
genitures, or the manner of their mixture, for
it is certain, and Fabricius admits it, that the
semen of the cock does not reach the cavity of
the uterus; neither is there any trace of the egg
to be discovered in the uterus immediately
after intercourse, and as its consequence, al-
though Aristotle himself repeatedly avers that
there is, asserting that ' 'something of the con-
ception forthwith ensues." But I shall by and
by demonstrate that neither does any such imag-
inary mixture of seminal fluids take place in
any animal, nor that immediately upon inter-
course, even of a fruitful kind, is there any-
thing in the shape of semen or blood, or of the
rudiments of an embryo present or demon-
strable in the cavity of the uterus. Nothing is
found in the egg or embryo which leads us to
suppose that the semen masculinum is either
there contained or mingled. The vulgar notion
of the chalazae being the tread of the cock is a
sheer mistake; and I am surprised, since there
are two of them, one in either end of the egg,
that no one has yet been found to maintain
that this was the cock's seed, that the hen's.
But this popular error is at once answered by
the fact that the chalazse are present with the
same characters in every egg, whether it be fer-
tile or barren.
EXERCISE 33. The male and the female are alike
efficient in the business of generation
The medical writers with propriety main-
tain, in opposition to the Aristotelians, that both
sexes have the power of acting as efficient
causes in the business of generation; inasmuch
as the being engendered is a mixture of the two
which engender: both form and likeness of
body, and species are mixed, as we see in the
hybrid between the partridge and common
fowl. And it does indeed seem consonant with
reason to hold that they are the efficient causes
of conception whose mixture appears in the
thing produced.
Aristotle entertaining this opinion says: "In
some animals it is manifest that such as the gen-
erator is, such is the engendered; not, however,
the same and identical, not one numerically,
but one specifically, as in natural things. A man
engenders a man, if there be nothing preter-
natural in the way, as a horse engenders a mule,
and other similar instances. For the mule is
common to the horse and the ass; it is not
spoken of as an allied kind; yet may horse and
ass both be there conjoined in a hybrid state."1
He says further in the same place: "It is enough
that the generator generate, and prove the
cause that the species be found in the matter:
for such and such an entire species is still found
associated with such and such flesh and bones —
here it is Gallias, there it is Socrates."
Wherefore if such an entire form, as a mule,
be a mixture of two, viz., a horse and an ass, the
horse does not suffice to produce this form of a
mule in the "matter"; but, as the entire form is
mixed, so another efficient cause is contributed
by the ass and added to that supplied by the
horse. That, therefore, which produces a mule
compounded of two, must itself be an "ade-
quate efficient," and mixed, if only "univocal."
For example, this woman and that man engen-
der this Socrates; not in so far as they are both
human beings, and of one and the same species,
but in so far as this man and that woman in
these bones and muscles constitute human
forms, of both of which, if Socrates be a certain
mixture, a compound of both, that by which
he is made must needs be a mixed univocal
compound of the two; /. e., a mixed efficient of
a mixed effect. And, therefore, it is that the
male and female by themselves, and separately,
are not genetic, but become so united in coitu,
and made one animal, as it were; whence, from
the two as one, is produced and educed that
which is the true efficient proximate cause of
conception.
The medical writers also, in directing their
attention to the particulars of human genera-
tion alone, come to conclusions on generation at
large; and the spermatic fluid proceeding from
the parents in coitu has in all probability beer
1 Metaphysics, vn. 8.
396
WILLIAM HARVEY
EXERCISE 34.
tion to the Aristotelians and tt
taken by them for true seed, analogous to the
seeds of plants. It is not without reason, there-
fore, that they imagine the mixed efficient
cause of the future offspring to be constituted
by a mixture of the seminal matters of each
parent. And then they go on to assert that the
mixture proceeding immediately from inter-
course is deposited in the uterus and forms the
rudiments of the conception. That things are
very different, however, is made manifest by
our preceding history of the egg, which is a
true conception.
, Of the matter of the egg, in opposi-
istotelians and the medical writers
The position taken up by the medical writers
against the Aristotelians, viz., that the blood is
not the first element in a conception, is clearly
shown from the generation of the egg to be
well chosen: neither during intercourse, nor be-
fore nor after it, is there a drop of blood con-
tained in the uterus of the fowl; neither are the
rudiments of eggs red, but white. Many ani-
mals also conceive in whose uteri, if they be
suddenly laid open after intercourse, no blood
can be demonstrated.
But when they contend that the maternal
blood is the food of the foetus in utero, especial-
ly of its more sanguineous parts, as they style
them, and that the foetus from the outset is as
it were a portion of the mother, being nour-
ished and growing through her blood, and veg-
etating through her spirit; so that neither does
the heart pulsate, nor the liver compose blood,
nor any part of the foetus perform any kind of
independent office, but everything is carried on
through the mother's means, they in their turn
are as certainly mistaken, and argue from er-
roneous observations. For the embryo in the
egg boasts of its own blood, formed from the
fluids contained within the egg; and its heart is
seen to pulsate from the very beginning: it bor-
rows nothing in the shape either of blood or
spirits from the hen, for the purpose of forming
its so-called sanguineous parts and its feathers;
as most clearly appears to anyone who looks on
with an unbiassed mind. From observations
afterwards to be communicated, I believe in-
deed that it will be held as sufficiently proven
that even the foetus of viviparous animals still
contained in the uterus is not nourished by the
blood of the mother and does not vegetate
through her spirit; but boasts of its own pecu-
liar vital principle and powers, and its own
blood, like the chick in wo.
With reference to the matter which the em-
bryo obtains from its male and female parent,
however, and the way and manner of genera-
tion as commonly discoursed of in the schools,
viz., that conception is produced or becomes
prolific from mixture of the genitures and their
mutual action and passion, as also of the semi-
nal fluid of the female, and the parts which are
spoken of as sanguineous and spermatic, num-
erous and striking observations afterwards to
be related have compelled me to adopt opin-
ions at variance with all such views. At this
time I shall only say that I am greatly surprised
how physicians, particularly those among them
who are conversant with anatomy, should pre-
tend to support their opinions by means of two
arguments especially, which rightly under-
stood, seem rather to prove the opposite; viz.,
from the shock and resolution of the forces and
the effusion of fluid which women at the mo-
ment of the sexual orgasm frequently expe-
rience, they argue that all women pour out a
seminal fluid, and that this is necessary to
generation.
But passing over the fact that the females of
all the lower animals, and all women, do not ex-
perience any such emission of fluid, and that
conception is nowise impossible in cases where
it does not take place, for I have known several,
who without anything of the kind were suf-
ficiently prolific, and even some who after ex-
periencing such an emission and having had
great enjoyment, nevertheless appeared to have
lost somewhat of their wonted fecundity; and
then an infinite number of instances might be
quoted of women who, although they have
great satisfaction in intercourse, still emit noth-
ing, and yet conceive; passing over these facts,
I say, I cannot but express surprise at those es-
pecially, who, conceiving such an emission on
the part of the female necessary to concep-
tion, have not adverted to the fact that the
fluid emitted is discharged, cast out, and is par-
ticularly abundant about the clitoris and orifice
of the vulva; that it is seldom poured out with-
in the vulva, never within the uterus, and so as
to be mingled with the semen of the male;
moreover, it is of a mere serous or ichorous con-
sistency, like urine, by no means thick and ap-
parently unctuous, like the spermatic matter
of the male. But how shall we suppose that to
be of use internally which is discharged exter-
nally ? Or shall we say that this humour, as if
bidding the uterus farewell, is taken to the
verge of the vulva, that it may be then recalled
with greater favour by the uterus?
The other argument is drawn from the geni-
ANIMAL GENERATION
397
tal organs of women, the testes, to wit, and vasa
spcrmatica, praeparantia et deferentia, which
are held to serve for the preparation of the
spermatic fluid. I, for my part, greatly wonder
how anyone can believe that from parts so im-
perfect and obscure a fluid like the semen, so
elaborate, concoct and vivifying, can ever be
produced, endowed with force and spirit and
generative influence adequate to overcome
that of the male; for this is implied in the dis-
cussion concerning the predominance of the
male or the female, as to which of them is to
become the agent and efficient cause, which
the matter and pathic principle. How should
such a fluid get the better of another concocted
under the influence of a heat so fostering, of
vessels so elaborate, and endowed with such
vital energy? — how should such a fluid as the
male semen be made to play the part of mere
matter? — But of these things more hereafter.
Meantime, it is certain that the egg of the
hen is not engendered from any such discharge
of fluid during sexual intercourse, although
after connexion, and brimful of satisfaction,
she shakes herself for joy, and, as if already pos-
sessed of the richest treasure, as if gifted by
supreme Jove, the preserver, with the blessing
of fecundity, she sets to work to prune and or-
nament herself. The pigeon, particularly that
kind which comes to us from Africa, expresses
the satisfaction she feels from intercourse in a
remarkable manner; she leaps, spreads her tail,
and sweeps the ground with its extremity, she
pecks and prunes her feathers— all her actions
are as if she felt raised to the summit of felicity
by the gift of fruitfulness.
We have said that the primary matter of the
egg does not consist of blood as Aristotle would
have it, neither does it proceed from any mix-
ture of the male and female seminal fluids.
Whence it truly originates we have already
stated in part in our history; and we shall by
and by have occasion to speak of the subject
more at length when we come to treat generally
of the matter from which every conception is
originally produced.
EXERCISE 35. In how far is the fowl efficient in
the generation of the egg, according to Aristotle?
And wherefore is the concurrence of the male
required?
It has been already stated that the cock and
hen are the two principles in the generation of
the egg, although of the manner in which they
are so I am of a different opinion from Aristotle
and medical authorities. From the production
of the egg we have clearly shown that the fe-
male as well as the male was efficient, and that
she had within her a principle whence motion
and the faculty of forming flowed; although in
the sexual act the male neither confers the mat-
ter, nor does the female eject any semen whence
the egg is constituted. It is consequently mani-
fest, in some animals at least, that nature has
not, on account of the distinction into male and
female, established it as a law that the one, as
agent, should confer form, the other, as passive,
supply matter, as Aristotle apprehended; nor
yet that during intercourse each should con-
tribute a seminal fluid, by the mixture of which
a conception or ovum should be produced, as
physicians commonly suppose.
Now since everything that has been delivered
by the ancients on generation is comprehended
in these two opinions, it appears to have es-
caped every one up to this time, first, why the
hen by herself does not generate, like vege-
tables, but requires a male to be associated with
her in the work; and then how the conception
or ovum is procreated by the male and the fe-
male together, or what either of them con-
tributes to the process, and for what end inter-
course was established.
Aristotle, in opposition to the entire tenor of
his hypothesis, viz., that the male is to be re-
garded as the agent, the female as supplying the
matter only, when he sees that eggs are actually
produced by hens without the concurrence of
the male, is compelled to admit that the female
is likewise efficient; he was further not ignorant
of the fact that an egg even when extruded
could preserve itself, nourish itself, increase in
size and produce an embryo, as happens with
the eggs of fishes; and he has besides accorded a
vital principle to an egg, even to a hypenemic
one. But he endeavours to explain to what ex-
tent a female is efficient, and how a hypenemic
egg is endowed with a vital principle, in the
passage where he says: "Hypenemic eggs ad-
mit of generation to a certain point; for that
they can ever go the length of producing an
animal is impossible, this being the work of the
senses. But females and all things that live, as
already repeatedly stated, possess the vegeta-
tive soul. Wherefore the hypenemic egg as a
vegetable is perfect, but as an animal it is im-
perfect."1 By this he seems to insinuate that
the hypenemic egg is possessed of a vegetative
soul, inasmuch as this is inherent in all things
that live, and an egg is alive. In like manner he
ascribes to the hen the power of creating and of
1 On the Generation of Animals, HI. 7.
WILLIAM HARVEY
conferring the vegetative soul; because all fe-
males acquire this virtue, so that a hypenemic
egg in so far as it lives as a vegetable is perfect,
in so far as it is an animal, however, it is imper-
fect. As if a male were not required that a con-
ception or ovum should be produced, and pro-
duced perfect; but that from this ovum an ani-
mal should be engendered. Not, I say, that an
egg be produced as perfect in all respects as is
the conception of a vegetable; but that it should
be imbued with the animal principle. The egg,
consequently, is formed by the hen, but it is
made prolific by the cock.
Aristotle adds in the same place: "There is a
distinction of sexes through the whole class of
birds. And, therefore, it happens that the hen
perfects her egg, not yet influenced by the in-
tercourse of the male, in so far as it is a plant;
but as it is not a plant, there she does not per-
fect it: nor does anything come of it which en-
genders. For neither has it arisen simply, like
the seed of a plant, nor like an animal concep-
tion, by intercourse." He is here speaking of the
wind egg; by and by he adds: "But those eggs
that are conceived through intercourse are al-
ready characterized in a portion of the albu-
men: such eggs become fruitful through the
male which first copulated, for they are then
supplied with both principles."
By this he seems to confess that the female is
also effective in the work of generation, or is
possessed of the faculty of engendering; be-
cause in every female there inheres a vegetative
soul, whose faculty it is to engender. And,
therefore, when he is speaking of the differences
between the male and female, he still acknowl-
edges both as generative; for he says: "We call
that animal male which engenders in another,
female that which engenders in itself." From
his own showing, therefore, both engender;
and as there is a vegetative soul inherent in
both, so is there also its faculty of generation.
But how they differ has already been shown in
the history of the egg: the hen generates of her-
self without the concurrence of the cock, as a
plant out of itself produces fruit; but it is a
wind egg that is thus produced: it is not made
fruitful without the concurrence of the cock
either preceding or succeeding. The female gen-
erates, then, but it is only up to a certain mark,
and the concurrence of the male is requisite
that this faculty of engendering be made com-
plete, that she may not only lay an egg, but
such an egg as will, under favorable circum-
stances, produce a pullet. The male appears to
be ordained by nature to supply this deficiency
in the generative powers of the female, as will
be clearly shown by and by, and that that
which the female of herself cannot accom-
plish, viz., the production of a fruitful egg,
may be supplied and made good by the act of
the male, who imparts this virtue to the fowl
or the egg.
EXERCISE 36. The perfect hen's egg is of two
colours
Every egg, then, is not perfect; but some are
to be held imperfect because they have not yet
attained their true dimensions, which they
only receive when extruded ; others are imperfect
because they are yet unprolific, and only ac-
quire a fertilizing faculty from without, such
are the eggs of fishes. Other eggs again are held
imperfect by Aristotle, because they are of one
colour only, inasmuch as perfect eggs consist of
yelk and albumen, and are of two colours, as if
better concocted, more distinct in their parts,
endowed with higher heat. The eggs that are
called centenine or hundredth eggs, and which
Fabricius1 will have it are engendered of certain
remainders of albumen, are of one colour only,
and by reason of their deficiency of heat and
their weakness, are regarded as imperfect. Of
all eggs, there are none more perfect than those
of the hen, which are produced complete in all
their fluids and appendages, of proper size and
fruitful.
Aristotle assigns the following reason where-
fore some eggs are of two colours, others of one
hue only: "In the hotter animals those things
from which the principles of their origin are
derived are distinct and separate from those
which furnish their nutrition; now the one of
these is white, the other is yellow."2 As if the
chick derived its origin from the albumen and
was nourished by the vitellus alone. In the same
place he proceeds thus: "That part which is
hot contributes properly to the form in the
constitution of the extremities; but the part
that is more earthy, and is farther removed,
supplies material for the trunk. Whence in eggs
of two colours the animal derives its origin from
the white, for the commencement of animal
existence is in the white; but the nourishment
is obtained from the yellow." He consequently
thinks that this is the reason why these fluids
are distinct, and why eggs are produced of two
colours.
Now these ideas are partly true, partly false.
It is not true, for instance, that the embryo of
1 Op. tit.) p. 10.
2 On the Generation of Animals^ m. I.
ANIMAL GENERATION
399
the common fowl is first formed from the albu-
men and then nourished by the vitellus; for,
from the history of the formation of the chick
in wo, from the course of the umbilical vessels
and the distribution of their branches, which
undoubtedly serve for obtaining nourishment,
it obviously appears that the constituent mat-
ter, and the nutriment are supplied to the
chick from its first formation by the yelk, as
well as the white; the fluid which we have
called the colliquament seems further to be
supplied, not less by the vitellus than the albu-
men; a certain portion of both the fluids seems,
in fact, to be resolved. And then the spot, by
the expansion of which the colliquament is
formed in the first instance, and which we have
called the eye, appears to be impressed upon
the membrane of the vitellus.
The distinction into yellow and white, how-
ever, seems to be a thing necessary : these mat-
ters, as they are undoubtedly of different na-
tures, appear also to serve different offices; they
are, therefore, completely separate in the per-
fect egg, one of them being more, the other
less, immediately akin to proper alimentary
matter; by the one the foetus is nourished from
the very beginning, by the other it is nour-
ished at a later period. For it is certain, as Fab-
ricius asserts, and as we afterwards maintain,
that both of them are truly nutritious, the al-
bumen as well as the vitellus, the albumen be-
ing the first that is consumed. I, therefore,
agree with Aristotle against the physicians, that
the albumen is the purer portion of the egg, the
better concocted, the more highly elaborated;
and, therefore, whilst the egg is getting per-
fected in the uterus, is the albumen as the hot-
ter portion poured around in the circumfer-
ence, the yelk or more earthy portion subsid-
ing to the centre. For the albumen appears to
contain the larger quantity of animal heat, and
so to be nutriment of a more immediate kind.
For like reasons it is probable that the albumen
is purer and better concocted externally than it
is internally.
When medical writers affirm that the yelk is
the hotter and more nutritious portion of the
egg, this I imagine is meant as it affords food to
us, not as it is found to supply the wants of the
chick in ovo. This, indeed, is obvious from the
history of the formation of the chick, by which
the thin albumen is absorbed and used up
sooner than the thick, as if it formed the more
appropriate aliment, and were more readily
transmuted into the substance of the embryo,
of the chick that is to be. The yelk, therefore,
appears to be a more distant or ultimate ali-
ment than the albumen, the whole of which
has been used up before any notable portion of
the vitellus is consumed. The yelk, indeed, is
still found inclosed within the abdomen of the
chick after its exclusion from the shell, as if it
were destined to serve the new being in lieu of
milk for its sustenance.
Eggs, consisting of white and yellow, are,
therefore, more perfect, as more distinct in
constitution, and elaborated by a higher tem-
perature. For in the egg there must be included
not only the matter of the chick but also its
first nutriment; and what is provided for a per-
fect animal, must, itself, be perfect and highly
elaborated; as that is, in fact, which consists of
different parts, some of which, as already
stated, are prior and purer, and so more easy of
digestion; others posterior, and therefore more
difficult of transmutation into the substance of
the chick. Now the yelk and albumen differ
from one another by such kinds of distinction.
Perfect eggs are, consequently, of two colours:
they consist of albumen and yelk, as if these
constituted fluids of easier or more difficult
digestion, adapted to the different ages and
vigour of the chick.
EXERCISE 37. Of the manner in which the egg is
increased by the albumen
From the history it appears that the rudi-
ments of the eggs in the ovary are of very small
size, mere specks, smaller than millet seeds,
white and replete with watery fluid: these
specks, however, by and by, become yelks, and
then surround themselves with albumen.
Aristotle seems to think that the albumen is
generated in the way of secretion from the vi-
tellus. It may be well to add his words: "The
sex," he says, "is not the cause of the double
colour, as if the white were derived from the
male, the yellow from the female; both are fur-
nished by the female. But one of them is hot,
the other is cold. Now these two portions are
distinct in animals fraught with much heat; in
those that are not so fraught the eggs are not
thus distinct. And this is the reason why the
conceptions of these are of one colour. But the
semen of the male alone sets the conception;
therefore is the conception of the bird small
and white in the first instance; but in the course
of time, and when there is a larger infusion of
blood, it becomes entirely yellow; and, last of
all, when the heat declines, the white portion,
as a humour of equal temperature surrounds it
on every side. For the white portion of the egg
4oo
WILLIAM HARVEY
is, by its nature, moist, and includes animal
heat in itself; and it is for this reason that it is
seen in the circumference, the yellow and
earthy portion remaining in the interior."1
Fabricius, however, thinks that "the albu-
men only adheres to the vitellus by juxtaposi-
tion. For while the yelk is rolled through the
second uterus and gradually descends, it also
gradually assumes to itself the albumen which
is there produced, and made ready, that it may
be applied to the yelk; until the yelk having
passed the middle spirals and reached the last
of them, already surrounded with the albumen,
it now surrounds itself with the membranes and
shell." Fabricius will, therefore, have it that
the egg increases in a two- fold manner: "partly
by means of the veins, as concerns the vitellus,
and partly by an appositive increase, as regards
the albumen."2 And, among other reasons, this
was perchance one for the above opinion: that
when an egg is boiled hard the albumen is
readily split into layers lying one over another.
But this also occurs to the yelk still connected
with the ovary, when boiled hard.
Wherefore, taught by experience, I rather in-
cline to the opinion of Aristotle; for the albu-
men is not merely perceived as added in the
way Fabricius will have it, but fashioned also,
distinguished by chalazae and membranes, and
divided into two different portions; and all this
in virtue of the inherence of the same vegeta-
tive vital principle by which the egg is more
conspicuously divided into two distinct sub-
stances—a yelk and a white. For the same fac-
ulty that presides over the formation of the
egg in general presides over the constitution of
each of its parts in particular. Neither is it al-
together true that the yelk is first formed and
the albumen added to it afterwards; for what is
seen in the ovary is not the vitellus of the egg,
but rather a compound containing the two liq-
uids mingled together. It has the colour of the
vitellus, indeed, but in point of consistence it is
more like the albumen; and when boiled hard
it is not friable like the proper yelk, but, like
the white, is concreted, jelly-like, and seen to
be composed of thin lamellae; and it has a kind
of white papula, or spot, in the middle.
Aristotle seems to derive this separation from
the dissimilar nature of the yelk and white; for
he says,8 as we have already stated, that if a
number of eggs be thrown into a pan and
boiled, in such wise that the heat shall not be
1 On the Generation of Animals, in. i.
1 Of. fit., p. 12.
* Fabricius, of. «*., p. 12.
quicker than the separation of the eggs (citatior
quam ovorum distinctio), the same thing will
take place in the mass of eggs which occurs in
the individual egg: the whole of the yelks will
set hi the middle, the whites round about them.
This I have myself frequently found to be
true on making the trial, and it is open to any-
one to repeat the experiment; let him only beat
yelks and whites together, put the mixture into
a dutch oven, or between two plates over the
fire, and having added some butter, cause it to
set slowly into a cake, he will find the albumen
covering over the yelks situated at the bottom.
EXERCISE 38. Of what the coc\ and hen severally
contribute to the production of the egg
Both cock and hen are to be reputed parents
of the chick; for both are necessary principles
of an egg, and we have proved both to be alike
its efficient: the hen fashions the egg, the cock
makes it fertile. Both, consequently, are instru-
ments of the plastic virtue by which this species
of animal is perpetuated.
But as in some species there appears to be no
occasion for males, females sufficing of them-
selves to continue the kind; so do we discover
no males among these, but females only, con-
taining the fertile rudiments of eggs in their in-
terior; in other species, again, none but males
are discovered which procreate and preserve
their kinds by emitting something into the
mud, or earth, or water. In such instances na-
ture appears to have been content with a single
sex, which she has used as an instrument ade-
quate to procreation.
Another class of animals has a generative
fluid fortuitously, as it were, and without any
distinction of sex; the origin of such animals is
spontaneous. But "as some things are made by
art, and some depend on accident, health for
example,"4 so also some semen of animals is not
produced by the act of an individual agent, as
in the case of a man engendered by a man; but
in some sort univocally, as in those instances
where the rudiments and matter, produced by
accident, are susceptible of taking on the same
motions as seminal matter, as in "animals
which do not proceed from coitus, but arise
spontaneously, and have such an origin as in-
sects which engender worms."5 For as mechan-
ics perform some operations with their un-
aided hands, and others not without the assist-
ance of particular tools; and as the more excel-
lent and varied and curious works of art require
4 Aristotle, On the Parts of Animals, 1. 1.
* On the Generation of Animals, in. 9.
ANIMAL GENERATION
401
a greater variety in the form and size of the
tools to bring them to perfection, inasmuch as
a greater number of motions and a larger
amount of subordinate means are required to
bring more worthy labours to a successful issue
— art imitating nature here as everywhere else,
so also does nature make use of a larger num-
ber and variety of forces and instruments as
necessary to the procreation of the more per-
fect animals. For the sun, or Heaven, or what-
ever name is used to designate that which is
understood as the common generator or parent
of all animated things, engenders some of them-
selves, by accident, without an instrument, as
it were, and equivocally; and others through
the concurrence of a single individual, as in
those instances where an animal is produced
from another animal of the same genus which
supplies both matter and form to the being en-
gendered; so in like manner in the generation of
the most perfect animals where principles are
distinguished, and the seminal elements of ani-
mated beings are divided, a new creation is not
effected save by the concurrence of male and
female, or by two necessary instruments. Our
hen's egg is of this kind; to its production in the
perfect state the cock and the hen are neces-
sary. The hen engenders in herself, and there-
fore does she supply place and matter, nutri-
ment and warmth; but the cock confers fecun-
dity; for the male, as Aristotle says,1 always per-
fects generation, secures the presence of a sen-
sitive vital principle, and from such an egg an
animal is engendered.
To the cock, therefore, as well as to the hen,
are given the organs requisite to the function
with which he is intrusted; in the hen all the
genital parts are adapted to receive and con-
tain, as in the cock they are calculated to give
and immit, or prepare that which transfers
fecundity to the female, he engendering, as it
were, in another, not in himself.
When we anatomize the organs appropriated
to generation, therefore, we readily distinguish
what each sex contributes in the process; for a
knowledge of the instruments here leads us by
a direct path to a knowledge of their functions.
EXERCISE 39. Of the coc^and the particulars most
remarkable in his constitution
The cock, as stated, is the prime efficient of
the perfect or fruitful hen's egg, and the chief
cause of generation: without the male no chick
would ever be produced from an egg, and in
many ovipara not even would any egg be pro-
1 Ibid., ii. 5.
duced. It is, therefore, imperative on us that
we look narrowly into his offices and uses, and
inquire particularly what he contributes to the
egg and chick, both in the act of intercourse
and at other times.
It is certain that the cock in coition emits his
"geniture," commonly called semen, from his
sexual parts, although he has no penis, as I
maintain; because his testes and long and am-
ple vasa deferentia are full of this fluid. But
whether it issues in jets, with a kind of spirit-
uous briskness and repeatedly as in the hotter
viviparous animals, or not, I have not been
able to ascertain. But as I do not find any vesi-
culae containing semen, from which, made brisk
and raised into a froth by the spirits, it might
be emitted; nor any penis through whose nar-
rower orifice it might be forcibly ejaculated,
and so strike upon the interior of the hen; and
particularly when I see the act of intercourse
so rapidly performed between them; I am dis-
posed to believe that the parts of the hen are
merely moistened with a very small quantity
of seminal fluid, only as much as will adhere to
the orifice of the pudenda, and that the prolific
fluid is not emitted by any sudden ejaculation;
so that whilst among animals repeated ejacula-
tions take place during the same connexion,
among birds, which are not delayed with any
complexity of venereal apparatus, the same ob-
ject is effected by repeated connexions. Ani-
mals that are long in connexion, copulate rare-
ly; and this is the case with the swan and ostrich
among birds. The cock, therefore, as he cannot
stay long in his connexions, supplies by dint of
repeated t readings the reiterated ejaculations
of the single intercourse in other animals; and
as he has neither penis nor glans, still the ex-
tremities of the vasa deferentia, inflated with
spirits when he treads, become turgid in the
manner of a glans penis, and the orifice of the
uterus of the hen, compressed by them, her
cloaca being exposed for the occasion, is
anointed with genital fluid, which consequently
does not require a penis for its intromission.
We have said, however, that such was the
virtue of the semen of the cock, that not only
did it render the uterus, the egg in utero, and
the vitelline germ in the ovary, but the whole
hen prolific, so that even the germs of vitelli,
yet to be produced, were impregnated.
Fabricius has well observed that the quantity
of spermatic fluid contained in the testes and
vasa deferentia of the cock was large; not that
the hen requires much to fecundate each of her
eggs, but that the cock may have a supply for
402
WILLIAM HARVEY
the laigc number of hens he serves and for his
repeated addresses to them.
The shortness and straight course of the
spermatic vessels in the cock also assist the rapid
emission of the spermatic fluid: anything that
must pass through lengthened and tortuous
conduits, of course, escapes more slowly and re-
quires a greater exercise of the impelling power
or spirit to force it away.
Among male animals there is none that is
more active or more haughty and erect, or that
has stronger powers of digestion than the cock,
which turns the larger portion of his food into
semen; hence it is that he requires so many
wives — ten or even a dozen. For there are some
animals, single males of which suffice for several
females, as we see among deer, cattle, &c.; and
there are others, of which the females are so
prurient that they are scarcely satisfied with
several males, such as the bitch and the wolf;
whence prostitutes were called lupas or wolves,
as making their persons common; and stews
were entitled lupanaria. Whilst some animals,
of a more chaste disposition, live, as it were, in
the conjugal estate, so that the male is married
to a single female only, and both take part in
providing for the wants of the family; for since
nature requires that the male supply the de-
ficiencies of the female in the work of genera-
tion, and as she alone in many cases does not
suffice to cherish and feed and protect the
young, the male is added to the wife that he
may take part in the burthen of bringing up the
offspring. Partridges lead a wedded life, be-
cause the females alone cannot incubate such a
number of eggs as they lay (so that they are
said, by some, to make two nests), nor to bring
up such a family as by and by appears without
assistance. The male pigeon also assists in build-
ing the nest, takes his turn in incubating the
eggs, and is active in feeding the young. In the
same way many other instances of conjugal life
among the lower animals might be quoted, and
indeed we shall have occasion to refer to several
in what yet remains to be said.
Those males, among animals, which serve
several females, such as the cock, have an
abundant secretion of seminal fluid, and are
provided with long and ample vasa deferentia.
And at whatever time or season the clustered
rudimentary papulae in the ovary come to
maturity and require fecundation, that they
may go on to be turned into perfect eggs, the
males will then be found to have an abundance
of seminal fluid, and the testicles to enlarge and
become conspicuous in the very situation to
which they transfer their fecundating influ-
ence, viz., the; praecordia. This is remarkable in
fishes, birds, and the whole race of oviparous
animals; the males of which teem with fecun-
dating seminal fluid at the same precise seasons
as the females become full of eggs.
Whatever parts of the hen, therefore, are
destined by nature for purposes of generation,
viz., the ovary, the infundibulum, the proc-
essus uteri, the uterus itself, and the pudenda;
as also the situation of these parts, their struc-
ture, dimensions, temperature, and all that fol-
lows this; all these, I say, are either subordinate
to the production and growth of the egg, or to
intercourse and the reception of fecundity
from the male; or, for the sake of parturition,
to which they conduce either as principal and
convenient means, or as means necessary,
and without which what is done could not be
accomplished; for nothing in nature 's works is
fashioned either carelessly or in vain. In the same
way all the parts in the cock are fashioned sub-
ordinate to the preparation or concoction of the
spermatic fluid, and its transference to the hen.
Now those males that are so vigorously con-
stituted as to serve several females are larger
and handsomer, and in the matter of spirit and
arms excel their females in a far greater degree
than the males of those that live attached to a
single female. Neither the male partridge, nor
the crow, nor the pigeon, is distinguished from
the female bird in the same decided way as the
cock from his hens, the stag from his does, &c.
The cock, therefore, as he is gayer in his
plumage, better armed, more courageous and
pugnacious, so is he replete with semen, and so
apt for repeated intercourse, that unless he
have a number of wives he distresses them by
his frequent assaults; he not only invites but
compels them to his pleasure, and leaping upon
them at inconvenient and improper seasons
(even when they are engaged in the business of
incubation) and wearing off the feathers from
their backs, he truly does them an injury. I
have occasionally seen hens so torn and worn by
the ferocious addresses of the cock, that with
their backs stript of feathers and laid bare in
places, even to the bone, they languished mis-
erably for a time and then died. The same thing
also occurs among pheasants, turkeys, and
other species.
EXERCISE 40. Of the hen
There are two instruments and two first
causes of generation, the male and the female —
for to the hen seems to belong the formation of
ANIMAL GENERATION
403
the egg, as to the cock the fertilizing principle.
In the act of intercourse, then, of these two,
that which renders the egg fruitful is either
transmitted from the male to the female, or by
means of coition is generated in the hen. The
nature of this principle, however, is no less dif-
ficult to ascertain than are the particulars of its
communication, whether, for instance, we sup-
pose such communication to take place with
the whole system of the hen, or simply with
her womb, or with the egg already formed, or
further, with all the eggs now commencing and
hereafter about to commence their existence in
the ovary. For it is probable, from what I have
formerly mentioned, and also from the experi-
ment of Fabricius,1 that but a few acts of inter-
course, and the consorting of the hen with the
cock for some days, are sufficient to fecundate
her, or at least her womb, during the whole
year. And so far I can myself affirm, from my
own observation, to wit, that the twentieth egg
laid by a hen, after separation from the cock,
has proved prolific. So that, in like manner as
it is well known that, from the seed of male
fishes shed into the water, a large mass of ova is
impregnated, and that in dogs, pigs, and other
animals, a small number of acts of intercourse
suffice for the procreation of many young ones
(some even think it well established, that if a
bitch have connexion more than three or four
times, her fruitfulness is impaired, and that
more females than males are then engendered),
so may the cock, by a few treadings, render pro-
lific not only the egg in the womb, but also the
whole ovarium, and, as has been often said, the
hen herself. Nay, what is more remarkable, and
indeed wonderful, it is said that in Persia,2 on
cutting open the female mouse, the young ones
still contained in the belly are already pregnant;
in other words, they are mothers before they
are born! as if the male rendered not only the
female fruitful, but also impregnated the young
which she had conceived; in the same way as
our cock fertilizes not merely the hen, but also
the eggs which are about to be produced by
her.
But this is confidently denied by those phy-
sicians who assert that conception is produced
from a mixture of the seed of each sex. And
hence Fabricius,3 although he affirms that the
seed of the cock ejected in coition never does,
nor can, enter the cavity of the womb, where
the egg is formed, or takes its increase, and
1 Op. at., p. 31.
3 Aristotle, History of Animals > vi. 37.
8 Of. cit.> pp. 38, 39.
though he plainly sees that the eggs when first
commencing in the ovarium are, no less than
those which exist in the womb, fecundated by
the same act of coition, and that of these no
part could arise from the semen of the cock,
yet has he supposed that this semen, as if it
must needs be present and permanent, is con-
tained during the entire year in the bursa of the
fruitful hen, and reserved in a foramen caecum.
This opinion we have already rejected, as well
because that cavity is found in the male and
female equally, as because neither there, nor
anywhere else in the hen, have we been able to
discover this stagnant semen of the cock; as
soon as it has performed its office, and im-
pressed a prolific power on the female, it either
escapes out of the body, or is dissolved, or is
turned into vapour and vanishes. And al-
though Galen,4 and all physicians with him, op-
pose by various reasonings this dissolving of
the semen, yet, if they carefully trace the ana-
tomical arrangement of the genital parts, and
at the same time weigh other proofs of the
strongest kind, they must confess that the
semen of the male, as it is derived from the
testicles through the vasa deferentia, and as it
is contained in the vesiculae seminales, is not
prolific unless it be rendered spiritual and effer-
vesce into a frothy nature by the incitement of
intercourse or desire. For it is not, as Aristotle5
bears witness, its bodily form, or fire, or any
such faculty, that renders the semen prolific,
but the spirit which is contained in it, and the
nature which inheres in it, bearing a propor-
tion to the element of the stars. Wherefore,
though we should allow with Fabricius that the
semen is retained in the bursa^ yet, when that
prolific effervescence or spirit had been spent,
it would forthwith be useless and sterile.
Hence, too, physicians may learn that the se-
men of the male is the architect of the progeny,
not because the first conception is embodied
out of it, but because it is spiritual and effer-
vescent, as if swelling with a fertilizing spirit,'
and a preternatural influence. For otherwise
the story of Averrhoes, of the woman who con-
ceived in a bath, might bear an appearance of
truth. But of these things more in their proper
place.
In the same manner then as the egg is formed
from the hen, so is it probable, that from the
females of other animals, as will hereafter be
shown, the first conceptions take both material
and form; and that, too, some little time after
4 cf. Aristotle, On the Generation of Animals, u, 3.
404
WILLIAM HARVEY
the semen of the male has been introduced, and
has disappeared again. For the cock does not
confer any fecundity on the hen, or her eggs,
by the simple emission of his semen, but only
in so far as that fluid has a prolific quality, and
is imbued with a plastic power; that is to say, is
spiritual, operative, and analogous to the es-
sence of the stars. The male, therefore, is no
more to be considered the first principle, from
which conceptions and the embryo arise, be-
cause he is capable of secreting and emitting
semen, than is the female, which creates an egg
without his assistance. But it is on this consid-
eration rather that he is entitled to his preroga-
tive, that he introduces his semen, imbued as
it is with the spirit and the virtue of a divine
agent, such as, in a moment of time, performs
its functions, and conveys fertility. For, as we
see things suddenly set on fire and blasted by a
spark struck from a flint, or the lightning flash-
ing from a cloud, so equally does the seed of the
male instantly affect the female which it has
touched with a kind of contagion, and transfer
to her its prolific quality, by which it renders
fruitful in a moment, not only the eggs, but
the uterus also, and the hen herself. For an
inflammable material is not set on fire by
the contact of flame more quickly than is the
hen made pregnant by intercourse with the
cock. But what it is that is transferred from
him to her, we shall afterwards find occasion to
speak of, when we treat this matter specially
and at greater length.
In the meantime, we must remark, that, if it
be derived from the soul (for whatever is fruit-
ful is probably endowed also with a soul; and
we have said before, that the egg, in Aristotle's
opinion, as well as the seeds of plants, has a
vegetative soul), that soul, or at all events the
vegetative one, must be communicated as a
graft, and transferred from the male to the fe-
male, from the female to the egg, from the egg
to the foetus; or else be generated in each of
these successively by the contagion of coition.
The subject, nevertheless, seems full of am-
biguity; and so Aristotle, although he allows
that the semen of the male has such great vir-
tue that a single emission of it suffices for fe-
cundating very many eggs at the same time,
yet, lest this admission should seem to gainsay
the efficacy of frequent repetitions of inter-
course, he further says, "In birds, not even
those eggs which arise through intercourse can
greatly increase in size, unless the intercourse
be continued; and the reason of this is that, as
in women, the menstrual excretion is drawn
downwards by sexual intercourse (for the uter-
us, becoming warm, attracts moisture, and its
pores are opened), so also does it happen with
birds, in which the menstrual excrement, be-
cause it accumulates gradually, and is retained
above the cincture, and cannot escape, from
being in small quantity, only passes off when it
has reached the uterus itself. For by this is the
egg increased, as is the foetus of the viviparous
animal by that which flows through the umbili-
cus. For almost all birds, after but a single act
of intercourse, continue to produce eggs, but
they are small."1
Now, so far perhaps would the opinion of
Aristotle be correct, that more and larger eggs
are procured by frequently-repeated inter-
course; because, as he says, there may be "a
flow of more fruitful material to the womb,
when warmed by the heat of coition"; not,
however, that frequent coition must neces-
sarily take place in order to render the eggs
that are laid prolific. For experience, as we have
said, teaches the contrary, and the reason which
he alleges does not seem convincing; since the
rudiments of eggs are not formed in the uterus
from menstrual blood, which is found in no
part of the hen, but in the ovary, where no
blood pre-exists, and originate as well without,
as along with the intercourse of the cock.
The hen, as well as all other females, supplies
matter, nutrition, and place to the conception.
The matter, whence the rudiments of all eggs
are produced in the ovary and take their in-
crease, seems to be the very same from which
all the other parts of the hen, namely, the
fleshy, nervous, and bony structures, as well as
the head and the rest of the members, are nour-
ished and grow. Nourishment is in fact con-
veyed to each single papula and yelk contained
in the ovary by means of vessels, in the same
way precisely as to all the other parts of the
hen. But the place where the egg is provided
with membranes, and perfected by the addition
of the chalazse and shell, is the uterus.
But that the hen neither emits any semen
during intercourse, nor sheds any blood into
the cavity of the uterus, and that the egg is not
formed in the mode in which Aristotle sup-
posed a conception to arise, nor, as physicians
imagine, from a mixture of the seminal fluids;
as also that the semen of the cock does not
penetrate into, nor is attracted towards, the
cavity of the uterus of the hen, is all made
manifestly clear by this one observation, name-
ly, that after intercourse there is nothing more
1 On the Generation of Animals % in. x.
ANIMAL GENERATION
405
to be found in the uterus, than there was be-
fore the act. And when this shall have been
afterwards clearly established and demon-
strated to be true of all kinds of animals which
conceive in a uterus, it will at the same time be
equally evident that what has hitherto been
handed down to us from all antiquity on the
generation of animals is erroneous; that the
foetus is not constituted of the semen either of
the male or female, nor of a mixture of the two,
nor of the menstrual blood, but that in all ani-
mals, as well in the prolific conception as after
it, the same series of phenomena occur as in the
generation of the chick from the egg, and as in
the production of plants from the seeds of their
several kinds. For, besides that, it appears the
male is not required as being in himself agent,
workman, and efficient cause; nor the female,
as if she supplied the matter; but that each,
male as well as female, may be said to be in
some sort the operative and parent; and the
foetus, as a mixture of both, is created a mixed
resemblance and kind. Nor is that true which
Aristotle often affirms, and physicians take for
granted, namely, that immediately after inter-
course, something either of the foetus or the
conception may be found in the uterus (for in-
stance, the heart, the "three bullae," or some
other principal part), at any rate something —
a coagulum, some mixture of the spermatic sub-
stances, or other things of the like kind. On the
contrary, it is not till long after intercourse
that the eggs and conception first commence
their existence, among the greater number of
animals, and these the most perfect ones; I
mean in the cases where the females have been
fruitful and have become pregnant. And that
the female is prolific, before any conception is
contained in the uterus, there are many indica-
tions, as will be hereafter set forth in the his-
tory of viviparous animals: the breasts enlarge,
the uterus begins to swell, and by other symp-
toms a change of the whole system is discerned.
But the hen, though she have for the most
part the rudiments of eggs in her before inter-
course, which are afterwards by this act ren-
dered fruitful, and there be, therefore, some-
thing in her immediately after coition, yet even
when she, as in the case of other animals, has as
yet no eggs ready prepared in the ovary, or has
at the time of the intercourse got rid of all she
had, yet does she by and by, even after some
lapse of time, as if in possession of both principles
or the powers of both sexes, generate eggs by
herself after the manner of plants; and these (I
speak from experience) not barren, but prolific.
Nay, what is more, if you remove all the eggs
from beneath a hen that has been fecundated
and is now sitting (after having already laid all
her eggs, and no more remain in the ovary),
she will begin to lay again; and the eggs thus
laid will be prolific, and have both principles
inherent in them.
EXERCISE 41. Of the sense in which the hen may
be called the * 'prime efficient" : and of her parturition
It has already been said that the hen is the
efficient cause of generation, or an instrument
of Nature in this work, not indeed immedi-
ately, or of herself; but when rendered prolific
by commission from, and in virtue of the male.
But as the male is considered by Aristotle to be
the first principle of generation on his own
merits, because the first impulse toward genera-
tion proceeds from him, so may the hen in
some measure be put down as the first cause of
generation; inasmuch as the male is undoubt-
edly inflamed to venery by the presence of the
female. "The female fish," says Pliny,1 "will
follow the male at the season of intercourse,
and strike his belly with her nose; at the spawn-
ing time the male will do the like to the fe-
male." I have myself at times seen male fishes
in shoals following a female that was on the
point of spawning, in the same way as dogs pur-
sue a bitch, that they might sprinkle the ova
just laid with their milk or seed. But this is
particularly to be remarked in the more wan-
ton and lascivious females, who stir up the dor-
mant fires of Cupid, and inspire a silent love;
hence it is that the common cock, so soon as he
sees one of his own hens that has been absent
for ever so short time, or any other stranger-
hen, forthwith feels the sting of desire, and
treads her. Moreover, victorious in a battle, al-
though wounded and tired from the fight, he
straightway sets about treading the wives of his
vanquished foe one after another. And that he
may further feed the flame of love thus kindled
in his breast, by various gesticulations, incite-
ments, and caresses, often crowing the while,
calling his hens to him, approaching and walk-
ing round them, and tripping himself with his
wings, he entices his females to intercourse as
by a kind of fascination. Such are the arts of the
male; but sometimes a certain sullenness of the
female, and an apparent disinclination on her
part, contribute not a little to arouse the ar-
dour of the male and stimulate his languishing
desire, so that he fills her more quickly and
more copiously with prolific spirit. But of al-
1 Hist, nat., ix. 50.
406
WILLIAM HARVEY
lurements of this kind, and in what degree they
promote conception, we shall speak more here-
after. For, if you carefully weigh the works of
nature, you will find that nothing in them was
made in vain, but that all things were ordered
with a purpose and for the sake of some good
end.
Almost all females, though they have pleas-
ure in the act of intercourse and impregnation,
suffer pain in parturition. But the reverse is the
case with the hen, who loudly complains dur-
ing intercourse and struggles against it; but in
parturition, although the egg be very large in
comparison with the body and the orifice of the
uterus, and it does nothing to further its exit
(as is customary with the young of viviparous
animals), yet she brings forth easily and with-
out pain, and immediately afterwards com-
mences her exultations; and with her loud
cackling calls the cock as it seems to share in her
triumph.
But, although many rudiments of eggs are
found in the hen's ovary, of various sizes and in
different stages, so that some are larger and
nearer to maturity than others, yet all of them
appear to be fecundated, or to receive the pro-
lific faculty from the tread of the cock at the
same time and in the same degree. And though
a considerable time elapse (namely, thirty or
more days) before the common hen or hen-
partridge lay all the eggs which she has con-
ceived, yet in a stated time after the mother
has begun to sit upon them (say twenty or two-
and-twenty days) all the young are hatched
nearly at the same time; nor are they less
perfect than if they had commenced their
origin simultaneously, from the period of one
and the same conception, as the whelps of
bitches do.
And while we are here, and while I think how
small are the prolific germs of eggs, mere papu-
lae and exudations less than millet-seeds, and
contemplate the full proportions of the cock
that springs from thence, his fine spirit, and his
handsome plumage, I cannot but express my
admiration that such strength should be re-
posed in the nature of things in such insignifi-
cant elements, and that it has pleased the om-
nipotent Creator out of the smallest beginnings
to exhibit some of his greatest works. From a
minute and scarce perceptible papula springs
the hen, or the cock, a proud and magnificent
creature. From a small seed springs a mighty
tree; from the minute gemmule or apex of the
acorn, how wide does the gnarled oak at length
extend his arms, how loftily does he lift his
branches to the sky, how deeply do his roots
strike down into the ground! "It is in truth a
great miracle of nature,'* says Pliny,1 "that
from so small an origin is produced a material
that resists the axe, and that supplies beams,
masts, and battering-rams. Such is the strength,
such the power of nature!" But in the seeds of
all plants there is a gemmule or bud of such a
kind, so small that if the top only, a very point,
be lost, all hope of propagation is immediately
destroyed; in so small a particle does all the
plastic power of the future tree seem lodged!
The provident ant by gnawing off this little
particle stores safely in her subterraneous hoard
the grain and other seeds she gathers, and in-
geniously guards against their growing: "The
cypress," adds Pliny, in the same place, "bears
a seed that is greatly sought after by the ant;
which makes us still further wonder that the
birth of mighty trees should be consumed in
the food of so small an animal." But on these
points we shall say more when we show that
many animals, especially insects, arise and are
propagated from elements and seeds so small as
to be invisible (like atoms flying in the air),
scattered and dispersed here and there by the
winds; and yet these animals are supposed to
have arisen spontaneously, or from decomposi-
tion, because their ova are nowhere to be
found. These considerations, however, may fur-
nish arguments to that school of philosophy
which teaches that all things are produced from
nothing; and indeed there is hardly any ascer-
tainable proportion between the rudiment and
the full growth of any animal.
Nor should we so much wonder what it is in
the cock that preserves and governs so perfect
and beautiful an animal, and is the first cause of
that entity which we call the soul; but much
more, what it is in the egg, aye, in the germ of
the egg, of so great virtue as to produce such an
animal, and raise him to the very summit of
excellence. Nor are we only to admire the
greatness of the artificer that aids in the pro-
duction of so noble a work, but chiefly the
"contagion" of intercourse, an act which is so
momentary! What is it, for instance, that
passes from the male into the female, from the
female into the egg, from the egg into the
chick? What is this transitory thing, which is
neither to be found remaining, nor touching,
nor contained, as far as the senses inform us,
and yet works with the highest intelligence and
foresight, beyond all art; and which, even after
it has vanished, renders the egg prolific, not be-
1 Ibid., XVH. 10.
ANIMAL GENERATION
407
cause it now touches, but because it formerly
did so, and that not merely in the case of the
perfect and completed egg, but of the imper-
fect and commencing one when it was yet but a
speck; aye, and makes the hen herself fruitful
before she has yet produced any germs of eggs,
and this too so suddenly, as if it were said by
the Almighty, "Let there be progeny," and
straight it is so?
Let physicians, therefore, cease to wonder at
what always excites their astonishment, name-
ly, the manner in which epidemic, contagious,
and pestilential diseases scatter their seeds, and
are propagated to a distance through the air,
or by somefomes producing diseases like them-
selves, in bodies of a different nature, and in a
hidden fashion silently multiplying themselves
by a kind of generation, until they become so
fatal, and with the permission of the Deity
spread destruction far and wide among man and
beast; since they will find far greater wonders
than these taking place daily in the generation
of animals. For agents in greater number and of
more efficiency are required in the construc-
tion and preservation of an animal, than for its
destruction; since the things that are difficult
and slow of growth, decay with ease and rapid-
ity. Seneca observes, with his usual elegance,
"How long a time is needed for conception to be
carried out to parturition! with what labour
and tenderness is an infant reared! to what dili-
gent and continued nutrition must the body be
subject, to arrive at adolescence! but by what a
nothing is it destroyed! It takes an age to es-
tablish cities, an hour to destroy them. By great
watching are all things established and made to
flourish, quickly and of a sudden do they fall in
pieces. That which becomes by long growth a
forest, quickly, in the smallest interval of time,
and by a spark, is reduced to ashes."1 Nor is
even a spark necessary, since by the solar rays
transmitted through a small piece of glass and
concentrated to a focus, fire may be immedi-
ately produced, and the largest things be set in
flames. So easy is everything to nature's maj-
esty, who uses her strength sparingly, and dis-
penses it with caution and foresight for the
commencement of her works by imperceptible
additions, but hastens to decay with sudden-
ness and in full career. In the generation of
things is seen the most excellent, the eternal
and almighty God, the divinity of nature,
worthy to be looked up to with reverence; but
all mortal things run to destruction of their
own accord in a thousand ways,
1 Nat. qu&st., in. 27.
EXERCISE 42. Of the manner in which the genera-
tion of the chicly ta%e$ place from the egg
Hitherto we have considered the egg as the
fruit and end; it still remains for us to treat of it
as the seed and beginning. "We must now in-
quire," says Fabricius2, "how the generation of
the chick results from the egg, setting out from
that principle of Aristotle and Galen, which is,
even conceded by all, to wit, that all things
which are made in this life, are manifestly
made by these three: workers, instruments, and
matter."
But since in natural phenomena, the work is
not extrinsic, but is included in the matter, or
the instruments, he concludes that we must take
cognizance only of the agent and the matter.
As we are here about to show in what manner
the chick arises from the egg, however, I think
it may be of advantage for me to preface this by
showing the number of modes in which one
thing may be said to be made from another.
For so it will appear, more clearly and dis-
tinctly, after which of these generation takes
place in the egg, and what are the right con-
clusions in regard to its matter, its instruments,
and efficient cause.
Aristotle has laid down that there are four
modes in which one thing is made from an-
other: "first, when we say that from day night
is made, or from a boy a man, since one is after
the other; secondly, when we say that a statue
is made from brass, or a bed from wood, or any-
thing else from a certain material, so that the
whole consists of something, which is inherent
and made into a form; thirdly, as when from a
musical man is made an unmusical one, or from
a healthy, a sick one, or contraries in any way:
fourthly, as Epicharmus exaggerates it, as of
calumnies, cursing; of cursing, fighting. But all
these are to be referred to that from whence
the movement took its rise; for the calumny is
a certain portion of the whole quarrel. Since
then these are the methods in which one thing
is made from another, it is clear that the seed is
in one of two of these. For that which is born
arises out of it, either as from matter, or as
from the prime mover. For it is not, 'as this is
after that,' in the same way as after the Pana-
thenoea navigation; nor as 'one contrary from
another'; for in such case, a thing would be
born out of its contrary, because it is in a state
of decay, and there must be something else as
subject-matter."8
2 Op. tit., p. 28.
* On the Generation of Animals, i. 18.
408
WILLIAM HARVEY
By these words, Aristotle rightly infers that
the semen proceeding from the male is the ef-
ficient or instrumental cause of the embryo;
since it is no part of what is born, either in the
first or third manner (namely, as one thing is
after another, or as it is out of its contrary) ; nor
does it arise from the subject-matter.
But then, as he adds, in the same place, "that
which comes out of the male in coition, is not
with truth and propriety called semen, but
rather geniture; and it is different from the
seed properly so called. For that is called the
geniture which, proceeding from the generant,
is the cause which first promotes the beginning
of generation. I mean in those creatures which
nature designed to have connexion; but the
seed is that which derives its origin from the in-
tercourse of the two (i.e., of the male and fe-
male) ; such is the seed of all plants; and of some
animals in which the sex is not distinct; it is the
produce, as it were, of the male and female
mixed together originally, like a kind of promis-
cuous conception"; and such as we have for-
merly in our history declared the egg to be,
which is called both fruit and seed. For the
seed and the fruit are distinct from each other,
and in the relation of antecedent and conse-
quent; the fruit is that which is out of some-
thing else, the seed is that out of which some-
thing else comes; otherwise, both were the
same.
It remains then, to inquire, in how many of
the aforesaid ways the foetus may arise, not in-
deed from the geniture of the male, but out of
the true seed, or out of the egg or conception,
which is in reality the seed of animals.
EXERCISE 43. In how many ways the chicly may
be said to be formed from the egg
It is admitted, then, that the foetus is formed
from a prolific egg, as out of the proper matter,
and as it were by the requisite agency, and that
the same egg stands for both causes of the
chick. For inasmuch as it derives its origin
from the hen, and is considered as a fruit, it is
the matter: but, in so far as it contains in its
whole structure the prolific and plastic faculty
infused by the male, it is called the efficient
cause of the chick.
Moreover, not only as Fabricius supposed,
are these, namely, the agent and the instru-
ment, inseparably joined in one and the same
egg, but it is also necessary that the aliment by
which the chick is nourished be present in the
same place. Indeed, in the prolific egg, these
four are found together, to wit, the agent, the
instrument, the matter, and the aliment, as we
have shown in our history.
Wherefore, we say, that the chick is formed
from the prolific egg in all the aforesaid ways,
namely, as from matter, by an efficient, and by
an instrument; and moreover, as a man grows
out of a boy, as the whole is made up of its
parts, and as a thing grows from its nutriment;
a contrary thing springs from a contrary.
For after incubation is begun, as soon as by
the internal motive principle a certain clear
liquid which we have called the eye of the egg
is produced, we say that that liquid is made, as
it were, out of a contrary; in the same way as
we suppose the chyle through concoction to be
formed out of its contraries (namely, crude ar-
ticles of food), and in the same way as we are
said to be nourished by contraries; so, from the
albumen is formed and augmented that to
which we have given the names of the eye and
the colliquament; and in the same manner,
from that clear fluid do the blood and pulsating
vesicle, the first particles of the chick, receive
their being, nutrition, and growth. The nutri-
ment, I say, is by the powers of an inherent
and innate heat, assimilated by means of con-
coction, as it were, out of a contrary. For the
crude and unconcocted are contrary to the con-
cocted and assimilated, as the unmusical man is
to the musical, and the sick to the sound man.
And when the blood is engendered from the
clear colliquament, or a clear fluid is produced
from the white or the yelk, there is generation
as regards the former, corruption as regards the
latter; a transmutation, namely, is made from
the extremes of contraries, the subject-matter
all the while remaining the same. To explain:
by the breaking up of the first form of the
white, the colliquament is produced; and from
the consumption of this colliquament, follows
the form of the blood, in the same way precisely
as food is converted into the substance of the
thing fed.
It is thus, then, that the chick is said to be
made out of the egg, as it were by a contrary;
for in the nutrition and growth of the chick in
the egg, white and yelk are equally broken up
and consumed, and finally the whole substance
of the egg. It is clear, therefore, that the chick
is formed from the egg, as it were, by a con-
trary, namely the aliment, and as if by an ab-
straction, and from a non-entity. For the first
particle of the chick, viz., the blood or punctum
saliens, is constituted out of something which is
not blood, and altogether its contrary, the
same subject-matter always remaining.
ANIMAL GENERATION
409
The chick too is made from the egg, as a man
is made from a boy. For in the same way, as out
of plants seeds arise, and out of seeds, buds,
sprouts, stems, flowers, and fruits; so also out
of the egg, the seed of the hen is produced, the
dilatation of the cicatricula and the colliqua-
ment, the blood and the heart, as the first par-
ticle of the foetus or fruit; and all this, in the
same way as the day from the night, the sum-
mer from the spring, a man from a boy — one
follows or comes after the other. So that, in the
same way as fruits arise after flowers on the
same stem, so likewise is the colliquament
formed after the egg, the blood after this, as
from the primogeneous humour, the chick after
the blood, and out of it, as the whole out of a
part; in the same way, as by Epicharmus' ex-
aggeration, out of calumnies comes cursing, and
out of cursing, fighting. For the blood first be-
gins its existence with the punctum saliens, and
at the same time, seems to be as well a part of
the chick, and a kind of efficient or instrument
of its generation, inseparable, as Fabricius
thinks, from the agent. But how the egg may
be called the efficient and instrument of genera-
tion, has partly been explained already, and
will be illustrated more copiously by what we
shall presently say.
So much has been fully established in our
history, that the punctum pulsans and the
blood, in the course of their growth, attach
round themselves the rest of the body, and all
the other members of the chick, just as the
yelk in the uterus, after being evolved from the
ovary, surrounds itself with the white; and this
not without concoction and nutrition. Now
the common instrument of all vegetative oper-
ations, is, in the opinion of all men, an internal
heat or calidum innatum, or a spirit diffused
through the whole, and in that spirit a soul or
faculty of a soul. The egg, therefore, beyond
all doubt, has its own operative soul, which is all
in the whole, and all in each individual part,
and contains within itself a spirit or animal
heat, the immediate instrument of that soul.
To one who should ask, then, how the chick is
made from the egg, we answer: after all the
ways recited by Aristotle, and devised by
others, in which it is possible for one thing to be
made from another.
EXERCISE 44. Fabricius is mistaken with regard to
the matter of the generation of the chicly in ovo
As I proposed to myself at the outset, I con-
tinue to follow Fabricius as pointing out the
way; and we shall, therefore, consider the three
things which he says are to be particularly re-
garded in the generation of the chick, viz. : the
agent, the matter, and the nourishment of the
embryo. These must needs be all contained in
the egg; he proposes various doubts or ques-
tions, and quotes the opinions of the most
weighty authorities in regard to them, these
opinions being frequently discordant. The first
difficulty is in reference to the matter and
nourishment of the chick. Hippocrates,1 An-
axagoras, Alcmaeon, Menander, and the an-
cient philosophers all thought that the chick
was engendered from the vitellus, and was
nourished by the albumen. Aristotle,2 however,
and after him, Pliny,3 maintained, on the con-
trary, that the chick was incorporated from the
albumen, and nourished by the vitellus. But
Fabricius himself, will have it that neither the
white nor yelk forms the matter of the chick;
he strives to combat both of the preceding
opinions, and teaches that the white and the
yellow alike do no more than nourish the chick.
One of his arguments, amongst a great number
of others which I think are less to be acquiesced
in, appears to me to have some force. The
branches of the umbilical vessels, he says,
through which the embryo undoubtedly im-
bibes its nourishment, are distributed to the al-
bumen and the vitellus alike, and both of these
fluids diminish as the chick grows. And it is on
this ground, that Fabricius in confirmation of
his opinion, says: "Of the bodies constituting
the egg, and adapted to forward the genera-
tion of the chick, there are only three, the al-
bumen, the vitellus, and the chalazae; now the
albumen and vitellus are the nourishment of
the chick; so that the chalazae alone remain as
matter from which it can be produced."4
Nevertheless, that the excellent Fabricius is
in error here, we have] demonstrated above in
our history. For after the chick is already al-
most perfected, and its head and its eyes are dis-
tinctly visible, the chalazae can readily be
found entire, far from the embryo, and pushed
from the apices towards the sides: the office of
these bodies, as Fabricius himself admits, is
that of ligaments, and to preserve the vitellus
in its proper position within the albumen. Nor
is that true, which Fabricius adds in confirma-
tion of his opinion, namely, that the chalazaeare
situated in the direction of the blunt part of the
1 De nat. pucri.
2 History of Animals, vi. 3; On the Generation of
Animals, in. i, 2.
8 Hist. nat. x. 53.
4 Op. «/., p. 34.
410
WILLIAM HARVEY
egg. For after even a single clay's incubation,
the relative positions of the fluids of the egg are
changed, the yelk being drawn upwards, and
the chalazae on either hand removed, as we
have already had occasion to say.
He is also mistaken when he speaks of the
chalazae, as proper parts of the egg. The egg
consists in fact but of white and yelk; the
chalazae as well as the membranes, are mere ap-
pendages of the albumen and vitellus. The
chalazae, in particular, are the extremities of
certain membranes, twisted and knotted; they
are produced in the same way as a rope is
formed by the contortion of its component fila-
ments, and exist for the purpose of more cer-
tainly securing the several elements of the egg
in their respective places.
Fabricius, therefore, reasons ill when he says,
that "the chalazae are found in the part of the
egg where the embryo is produced, wherefore
it is engendered from them"; for even on his
own showing, this could never take place, he
admitting that the chalazae are extant in either
extremity of the egg, whilst the chick never
makes its appearance save at the blunt end; in
which, moreover, at the first commencement
of generation, no chalaza can be seen. Further,
if you examine the matter in a fresh egg, you
will find the superior chalaza not immediately
under the blunt end or its cavity, but declined
somewhat to the side; not to that side, how-
ever, where the cavity is extending, but rather
to the opposite side. Still further, from what has
preceded, it is obvious that the relative posi-
tions of the fluids of the egg are altered im-
mediately that incubation is begun: the eye in-
creased by the colliquament is drawn up to-
wards the cavity in the blunt end of the egg,
whence the white and the chalaza are on either
hand withdrawn to the side. For the macula or
cicatricula which before incubation was situated
midway between the two ends, now increased
into the eye of the egg, adjoins the cavity in
the blunt end, and whilst one of the chalazae is
depressed from the blunt end, the other is
raised from the sharp end, in the same way as
the poles of a globe are situated when the axis
is set obliquely; the greater portion of the al-
bumen, particularly that which is thicker, sub-
sides at the same time, into the sharp end.
Neither is it correct to say that the chalazae
bear a resemblance in length and configuration
to the chick on its first formation, and that the
number of their nodules corresponds with the
number of the principal parts of the embryo; a
statement which gives Fabricius an opportu-
nity of adducing an argument connected with
the matter of the chick, based on the similarity
of its consistency to that of the chalazae. But
the red mass (which Fabricius regarded as the
liver) is neither situated in nor near the chalaza,
but in the middle of the clear colliquament;
and it is not any rudiment of the liver but of
the heart alone. Neither does his view square
with the example he quotes of the tadpole, "of
which/' he says, "there is nothing to be seen
but the head and the tail, that is to say, the
head and spine, without a trace of upper or
lower extremities." And he adds, "he who has
seen a chalaza, and this kind of conception, in
so far as the body is concerned, will believe
that in the former, he has already seen the lat-
ter." I, however, have frequently dissected the
tadpole, and have found the belly of large size,
and containing intestines and liver and heart
pulsating; I have also distinguished the head
and the eyes. The part which Fabricius takes
for the head, is the rounded mass of the tad-
pole, whence the creature is called gynnus, from
its circular form. It has a tail with which it
swims, but is without legs. About the epoch of
the summer solstice, it loses the tail, when the
extremities begin to sprout. Nothing however
occurs in the nature of a division of the embryo
pullet into the head and spine, which should in-
duce us to regard it as produced from the cha-
lazae, and in the same manner as the tadpole.
The position and fame of Fabricius, however,
a man exceedingly well skilled in anatomy, do
not allow me to push this refutation further.
Nor indeed, is there any necessity so to do, see-
ing that the thing is so clearly exhibited in our
history.
Our author concludes, by stating that his
opinion is of great antiquity, and was in vogue
even in the times of Aristotle.
For my own part, nevertheless, I regard the
view of Ulysses Aldrovandus as the older, he
maintaining that the chalazae are the spermatic
fluid of the cock, from which and through
which alike the chick is engendered.
Neither notion, however, is founded on fact,
but is the popular error of all times: the
chalazae, treads, or treadles, as our English
name implies, are still regarded by the country
folks as the semen of the cock.
"The treadles (grandines)" says Aldrovan-
dus: "are the spermatic fluid of the cock, be-
cause no fertile egg is without them." But nei-
ther is any unprolific egg without these parts,
a fact which Aldrovandus was either ignorant
of or concealed. Fabricius admits this fact; but
ANIMAL GENERATION
411
though he has denied that the semen of the
male penetrates to the uterus or is ever found
in the egg, he, nevertheless, contends that the
chalazae alone of all the parts of the egg are im-
pregnated with the prolific power of the egg,
and are the repositories of the fecundating in-
fluence; and this, with the fact staring him in
the face all the while that there is no percepti-
ble difference between the chalazae of a prolific
and an unprolific egg. And when he admits that
the mere rudiments of eggs in the ovary, as
well as the vitelli that are surrounded with al-
bumen, become fecundated through the inter-
course of the cock, I conceive that this must
have been the cause of the error committed by
so distinguished an individual. It was the cur-
rent opinion, as I have said oftener than once,
both among philosophers and physicians, that
the matter of the embryo in animal generation,
was the geniture, either of the male, or of the
female, or resulted from a mixture of the two,
and that from this, deposited in the uterus, like
a seed in the ground, which produces a plant,
the animal was engendered. Aristotle, himself,
is not very far from the same view, when he
maintains the menstrual blood of the female to
be the seed, which the semen of the male coagu-
lates, and so composes the conception.
The error which we have announced, having
been admitted by all in former times, as a mat-
ter of certainty, it is not to be wondered at
that various erroneous opinions, based on each
man's conjecture, should have emanated from
it. They, however, are wholly mistaken, who
fancy that anything in the shape of a "pre-
pared or fit matter" must necessarily remain in
the uterus after intercourse, from which the
foetus is produced, or the first conception is
formed, or that anything is immediately fash-
ioned in the uterine cavity that corresponds
to the seed of a plant deposited in the bosom
of the ground. For it is quite certain that, in
the uterus of the fowl, and the same thing is
true of the uterus of every other female animal,
there is nothing discoverable after intercourse
more than there was before it.
It appears, consequently, that Fabricius
erred when he said: "In the same way as a vivi-
parous animal is incorporated from a small
quantity of seminal matter, whilst the matter
which is taken up as food and nourishment is
very large; so a small chalaza suffices for the
generation of a chick, and the rest of the mat-
ter contained in the egg goes to it in the shape
of nutriment/'1 From which it is obvious, that
* Of. tup. cit.t p. 35.
he sought for some such "prepared matter"
in the egg, whence the chick should be incor-
porated; mainly, as it seems, that he might not
be found in contradiction with Aristotle's def-
inition of an egg, viz. : as "that from part of
which an animal is engendered; and the remain-
der of which is food for the thing engendered/'2
This of Fabricius, therefore, has the look of a
valid argument, namely, "Since there are only
three parts in the egg— the albumen, the vitel-
lus, and the chalazae; and the two former alone
supply aliment; it necessarily follows that the
chalazae alone are the matter from which the
chick is constituted."
Thus, our learned anatomist, blinded by a
popular error, seeking in the egg for some par-
ticular matter fitted to engender the chick dis-
tinct from the rest of the contents of the egg,
has gone astray. And so it happens to all, who,
forsaking the light, which the frequent dis-
section of bodies, and familiar converse with
nature supplies, expect that they are to under-
stand from conjecture, and arguments founded
on probabilities, or the authority of writers,
the things or the facts which they ought them-
selves to behold with their own eyes, to per-
ceive with their proper senses. It is not wonder-
ful, therefore, when we see that we have so
many errors accredited by general consent,
handed down to us from remote antiquity, that
men otherwise of great ingenuity, should be
egregiously deceived, which they may very
well be, when they are satisfied with taking
their knowledge from books, and keeping their
memory stored with the notions of learned
men. They who philosophize in this way, by
tradition, if I may so say, know no better than
the books they keep by them.
In the egg then, as we have said, there is no
distinct part or prepared matter present, from
which the foetus is formed ; but in the same way
as the apex or gemmule protrudes in a seed ; so in
the egg, there is a macula or cicatricula, which,
endowed with plastic power, grows into the eye
of the egg and the colliquament, from which and
in which the primordial or rudimentary parts
of the chick, the blood, to wit, and the punc-
tum saliens are engendered, nourished, and
augmented, until the perfect chick is developed.
Neither is Aristotle's definition of an egg cor-
rect, as a body from part of which an embryo is
formed, and by part of which it is nourished,
unless the philosopher is to be understood in the
following manner: the egg is a body, from part
of which the chick arises, not as from a special
2 History of Animals t HI. 8.
412
WILLIAM HARVEY
matter, but as a man grows out of a boy; or an
egg is a perfect conception from which the
chick is said to be partly constituted, partly
nourished; or to conclude, an egg is a body, the
fluids of which serve both for the matter and
the nourishment of the parts of the foetus. In
this sense, indeed, Aristotle teaches us that the
matter of the human foetus is the menstrual
blood; "which (when poured into the uterus by
the veins) nature employs to a new purpose;
viz., that of generation, and that a future being
may arise, such as the one from which it
springs; for potentially it is already such as is
the body whose secretion it is, namely the
mother/'1
EXERCISE 45. What is the material of the chicly
and how it is formed in the egg
Since, then, we are of opinion that for the ac-
quisition of truth we cannot rely on the theories
of others, whether these rest on mere assertions,
or even may have been confirmed by plausible
arguments, except there be added thereto a
diligent course of observation; we propose to
show, by clearly-arranged remarks derived
from the book of nature, what is the material of
the foetus, and in what manner it thence takes
its origin. We have seen that one thing is made
out of another (tanquam ex materia) in two
ways, and this as well in works of art, as in
those of nature, and more particularly in the
generation of animals.
One of these ways, viz., when the object is
made out of something pre-existing, is exem-
plified by the formation of a bed out of wood,
or a statue from stone; in which case, the whole
material of the future piece of work has already
been in existence, before it is finished into
form, or any part of the work is yet begun; the
second method is, when the material is both
made and brought into form at the same time.
Just then as the works of art are accomplished
in two manners, one, in which the workman
cuts the material already prepared, divides it,
and rejects what is superfluous, till he leaves it
in the desired shape (as is the custom of the stat-
uary); the other, as when the potter educes a
form out of clay by the addition of parts, or in-
creasing its mass, and giving it a figure, at the
same time that he provides the material, which
he prepares, adapts, and applies to his work
(and in this point of view, the form may be
said rather to have been made than educed);
so exactly is it with regard to the generation of
animals.
1 On the Generation of Animals , xi. 4.
Some, out of a material previously concocted,
and that has already attained its bulk, receive
their forms and transfigurations; and all their
parts are fashioned simultaneously, each with
its distinctive characteristic, by the process
called metamorphosis, and in this way a perfect
animal is at once born; on the other hand, there
are some in which one part is made before
another, and then from the same material,
afterwards receive at once nutrition, bulk, and
form: that is to say, they have some parts made
before, some after others, and these are at the
same time increased in size and altered in form.
The structure of these animals commences from
some one part as its nucleus and origin, by the
instrumentality of which the rest of the limbs
are joined on, and this we say takes place by the
method of epigenesis, namely, by degrees, part
after part; and this is, in preference to the
other mode, generation properly so called.
In the former of the ways mentioned, the
generation of insects is effected where by meta-
morphosis a worm is born from an egg; or out
of a putrescent material, the drying of a moist
substance or the moistening of a dry one, rudi-
ments are created, from which, as from a cater-
pillar grown to its full size, or from an aurelia,
springs a butterfly or fly already of a propel
size, which never attains to any larger growth
after it is first born; this is called metamor-
phosis. But the more perfect animals with red
blood are made by epigenesis, or the superad-
dition of parts. In the former, chance or hazard
seems the principal promoter of generation,
and there, the form is due to the potency of a
pre-existing material; and the first cause of
generation is "matter," rather than "an exter-
nal efficient"; whence it happens too that these
animals are less perfect, less preservative of
their own races, and less abiding than the red-
blooded terrestrial or aquatic animals, which
owe their immortality to one constant source,
viz., the perpetuation of the same species; of
this circumstance we assign the first cause to
nature and the vegetative faculty.
Some animals, then, are born of their own
accord, concocted out of matter spontaneously,
or by chance, as Aristotle seems to assert, when
he speaks of animals whose matter is capable of
receiving an impulse from itself, viz., the same
impulse given by hazard, as is attributable to
the seed, in the generation of other animals.
And the same thing happens in art, as in the
generation of animals. Some things, which are
the result of art, are so likewise of chance, as
good health; others always owe their existence
ANIMAL GENERATION
to art; for instance, a house. Bees, wasps, but-
terflies, and whatever is generated from cater-
pillars by metamorphosis, are said to have
sprung from chance, and, therefore, to be not
preservative of their own race; the contrary is
the case with the lion and the cock; they owe
their existence, as it were, to nature or an oper-
ative faculty of a divine quality, and require
for their propagation an identity of species,
rather than any supply of fitting material.
In the generation by metamorphosis forms
are created as if by the impression of a seal, or
as if they were adjusted in a mould; in truth,
the whole material is transformed. But an
animal which is created by epigenesis attracts,
prepares, elaborates, and makes use of the ma-
terial, all at the same time; the processes of
formation and growth are simultaneous. In the
former the plastic force cuts up, and distributes,
and reduces into limbs the same homogeneous
material; and makes out of a homogeneous ma-
terial organs which are dissimilar. But in the
latter, while it creates in succession parts which
are differently and variously distributed, it re-
quires and makes a material which is also vari-
ous in its nature, and variously distributed, and
such as is now adapted to the formation of one
part, now of another; on which account we be-
lieve the perfect henYegg to be constituted of
various parts.
Now it appears clear from my history that
the generation of the chick from the egg is the
result of epigenesis, rather than of metamor-
phosis, and that all its parts are not fashioned
simultaneously, but emerge in their due suc-
cession and order; it appears, too, that its form
proceeds simultaneously with its growth, and
its growth with its form; also that the genera-
tion of some parts supervenes on others pre-
viously existing, from which they become dis-
tinct; lastly, that is origin, growth, and con-
summation are brought about by the method of
nutrition; and that at length the foetus is thus
produced. For the formative faculty of the
chick rather acquires and prepares its own ma-
terial for itself than only finds it when pre-
pared, and the chick seems to be formed and to
receive its growth from no other than itself.
And, as all things receive their growth from the
same power by which they are created, so like-
wise should we believe that by the same power
by which the chick is preserved, and caused to
grow from the commencement (whether that
may have been the soul or a faculty of the soul),
by that power, I say, is it also created. For the
same efficient and conservative faculty is found
in the egg as in the chick; and of the same ma-
terial of which it constitutes the first particle
of the chick, out of the very same does it
nourish, increase, and superadd all the other
parts. Lastly, in generation by metamorphosis
the whole is distributed and separated into
parts; but in that by epigenesis the whole is put
together out of parts in a certain order, and
constituted from them.
Wherefore Fabricius was in error when he
looked for the material of the chick (as a dis-
tinct part of the egg, from which its body was
formed), as if the chick were created by meta-
morphosis, or a transformation of the material
in mass; and as if all, or at least the principal
parts of the body sprang from the same ma-
terial, and, to use his own words, were incor-
porated simultaneously. [He is, therefore, of
course, opposed to the notion] of the chick
being formed by epigenesis, in which a certain
order is observed according to the dignity and
the use of parts, where at first a small founda-
tion is, as it were, laid, which, in the course of
growth, has at one and the same time distinct
structures formed and its figure established,
and acquires an additional birth of parts after-
wards, each in its own order; in the same way,
for instance, as the bud bursting from the top
of the acorn, in the course of its growth, has its
parts separately taking the form of root, wood,
pith, bark, boughs, branches, leaves, flowers,
and fruit, until at length out comes a perfect
tree; just so is it with the creation of the chick
in the egg: the little cicatrix, or small spot, the
foundation of the future structure, grows into
the eye and is at the same time separated into
the colliquament; in the centre of which the
punctum sanguineum pulsans commences its
being, together with the ramification of the
veins; to these is presently added the nebula,
and the first concretion of the future body; this
also, in proportion as its bulk increases, is grad-
ually divided and distinguished into parts,
which however do not all emerge at the same
time, but one after the other, and each in its
proper order. To conclude, then: in the genera-
tion of those animals which are created by
epigenesis, and are formed in parts (as the chick
in the egg), we need not seek one material for
the incorporation of the foetus, another for its
commencing nutrition and growth; for it re-
ceives such nutrition and growth from the same
material out of which it is made; and, vice ver-
sa, the chick in the egg is constituted out of the
materials of its nutrition and growth. And an
animal which is capable of nutrition is of the
414
WILLIAM HARVEY
same potency as one which is augmentative, as
we shall afterwards show; and they differ only,
as Aristotle says, in their distinctness of being;
in all other respects they are alike. For, in so
far as anything is convertible into a substance,
it is nutritious, and under certain conditions it
is augmentative: in virtue of its repairing a
loss of substance, it is called nutriment, in vir-
tue of its being added, where there is no such
loss of substance, it is called increment. Now the
material of the chick, in the processes of genera-
tion, nutrition, and augmentation is equally to
be considered as aliment and increment. We say
simply that anything is generated, when no
part of it has pre-existed; we speak of its being
nourished and growing when it has already ex-
isted. The part of the foetus which is first
formed is said to be begotten or born; all sub-
stitutions or additions are called adnascent, or
aggenerate. In all there is the same transmuta-
tion or generation from the same to the same;
as concerns a part, this is performed by the
process of nutrition and augmentation, but as
regards the whole, by simple generation; in
other respects the same processes occur equally.
For from the same source from which the ma-
terial first takes its existence, from that source
also does it gain nutriment and increase. More-
over, from what we shall presently say, it will
be made clear that all the parts of the body are
nourished by a common nutritious juice; for,
as all plants arise from one and the same com-
mon nutriment (whether it be dew or a mois-
ture from the earth), altered and concocted in a
diversity of manners, by which they are also
nourished and grow; so likewise to identical
fluids of the egg, namely, the albumen and the
yelk, do the whole chick and each of its parts
owe their birth and growth.
We will explain, also, what are the animals
whose generation takes place by metamorpho-
sis, and of what kind is the pre-existent material
of insects which take their origin from a worm
or a caterpillar; a material from which, by
transmutation alone, all their parts are simul-
taneously constituted and embodied, and a per-
fect animal is born; likewise, to what animals
any constant order in the successive generation
of their parts attaches, as is the case with such
as are at first born in an imperfect condition,
and afterwards grow to maturity and perfec-
tion; and this happens to all those that are born
from an egg. As in these the processes of growth
and formation are carried on at the same time,
and a separation and distinction of parts takes
place in a regularly observed order, so in their
case is there no immediate pre-existing ma-
terial present, for the incorporation of the
foetus (such as the mixture of the semina of the
male and female is generally thought to be, or
the menstrual blood, or some very small por-
tion of the egg), but as soon as ever the ma-
terial is created and prepared, so soon are
growth and form commenced; the nutriment is
immediately accompanied by the presence of
that which it has to feed. And this kind of gen-
eration is the result of epigenesis as the man
proceeds from the boy; the edifice of the body,
to wit, is raised on the punctum saliens as a
foundation; as a ship is made from a keel, and as
a potter makes a vessel, as the carpenter forms
a footstool out of a piece of wood, or a statuary
his statue from a block of marble. For out of
the same material from which the first part of
the chick or its smallest particle springs, from
the very same is the whole chick born; whence
the first little drop of blood, thence also pro-
ceeds its whole mass by means of generation in
the egg; nor is there any difference between the
elements which constitute and form the limbs
or organs of the body, and those out of which
all their similar parts, to wit, the skin, the flesh,
veins, membranes, nerves, cartilages, and bones,
derive their origin. For the part which was at
first soft and fleshy, afterwards, in the course of
its growth, and without any change in the mat-
ter of nutrition, becomes a nerve, a ligament,
a tendon; what was a simple membrane becomes
an investing tunic; what had been cartilage is
afterwards found to be a spinous process of
bone, all variously diversified out of the same
similar material. For a similar organic body
(which the vulgar believe to consist of the ele-
ments) is not created out of elements at first
existing separately, and then put together,
united, and altered; nor is it put together out of
constituent parts; but, from a transmutation of
it when in a mixed state, another compound is
created: to take an instance, from the colli-
quament the blood is formed, from the blood
the structure of the body arises, which appears
to be homogeneous in the beginning, and re-
sembles the spermatic jelly; but from this the
parts are at first delineated by an obscure divi-
sion, and afterwards become separate and dis-
tinct organs.
Those parts, I say, are not made similar by
any successive union of dissimilar and hetero-
geneous elements, but spring out of a similar
material through the process of generation,
have their different elements assigned to them
by the same process, and are made dissimilar.
ANIMAL GENERATION
Just as if the whole chick was created by a com-
mand to this effect, of the Divine Architect:
"Let there be a similar colourless mass, and let
it be divided into parts and made to increase,
and in the meantime, while it is growing, let
there be a separation and delineation of parts;
and let this part be harder, and denser, and
more glistening, that be softer and more col-
oured/' and it was so. Now it is in this very
manner that the structure of the chick in the
egg goes on day by day; all its parts are formed,
nourished, and augmented out of the same ma-
terial. First, from the spine arise the sides, and
the bones are distinguishable from the flesh by
minute lines of extreme whiteness; in the head
three bullas are perceived, full of crystalline
fluid, which correspond to the brain, the cere-
bellum, and one eye, easily observable by a
black speck; the substance which at first ap-
pears a milky coagulum, afterwards gradually
becomes cartilaginous, has spinous processes at-
tached to it, and ends in being completely os-
seous; what was at first of a mucous nature and
colourless, is converted at length into red flesh
and parenchyma; what was at one time limpid
and perfectly pure water, presently assumes the
form of brain, cerebellum, and eyes. For there
is a greater and more divine mystery in the
generation of animals than the simple collect-
ing together, alteration, and composition of a
whole out of parts would seem to imply; inas-
much as here the whole has a separate constitu-
tion and existence before its parts, the mixture
before the elements. But of this more at an-
other time, when we come to specify the causes
of these things.
EXERCISE 46. Of the efficient cause of the genera-
tion of the chicly and foetus
We have thus far spoken of the matter from
which the chick in ovo is generated. We have
still with Fabricius to say a few words on the
efficient cause of the chick. As this subject is
surrounded with difficulties, however; as writ-
ers nowhere else dispute more virulently or
more wordily, and Aristotle himself in explain-
ing the matter is singularly intricate and per-
plexed, and as various questions that can by no
means be lightly treated do in fact present
themselves for consideration, I conceive that I
shall be undertaking a task worthy of the toil
if, as I have done in the disquisition on the
"matter," I set out here by stating in how
many ways anything can be said to be "ef-
ficient" or "effective." We shall thus obtain a
clearer idea of what it is which we are to in-
quire after under the name of "efficient," and
further, what estimate we are to form of the
ideas of writers upon this subject; it will at the
same time appear from our observations what
is truly and properly to be called "an efficient."
Aristotle defines an efficient cause to be that
"whence is derived the first principle of change
or quiescence; as a counsel, a father; and sim-
ply as doing that which is done; the transmute
of the thing transmuted."1 In the generation of
animals, accordingly, many and various kinds
of causes inducing motion are brought forward;
sometimes an accident or quality is assigned;
and so animal heat and the formative faculty
are called efficient causes. Sometimes it is an ex-
ternal substance, previously existing, in which
inheres the plastic force or formative faculty
that is designated in the same way ; as the cock
or his seminal fluid, by the influence of which
the chick is procreated from the egg. Occasion-
ally it is some internal substance, self-existent,
such as spirit, or innate heat. And again, it is
some other substance, such as form, or nature,
or soul, or some portion of the vegetative soul,
that is regarded as the efficient, such a principle
as we have already declared to inhere in the
egg.
Besides, since one thing whence motion pro-
ceeds is nearer and another more remote, it
sometimes happens that the media between the
prime efficient and the thing last effected, and
instruments are regarded as efficient causes;
subordinate conclusions, likewise, or the prin-
ciples of subsequents, are reckoned among the
number of efficient causes; in this way some
parts are themselves spoken of as genital parts,
such as the heart, whence Aristotle affirms that
all the rest of the body is produced; a state-
ment which we have found borne out by our
history. The heart, I repeat, or at all events its
rudimentary parts, namely, the vesicle and
pulsating point, construct the rest of the body
as their future dwelling-place; when erected it
enters and conceals itself within its habitation,
which it vivifies and governs, and applying the
ribs and sternum as a defence, it walls itself
about. And there it abides, the household div-
inity, first seat of the soul, prime receptacle of
the innate heat, perennial centre of animal ac-
tion; source and origin of all the faculties; only
solace in adversity !
Moreover, since the "efficient" is so styled
with reference to the effect, as some parts pro-
duced by epigenesis are posterior in order to
other parts, and are different from antecedent
1 Metaphysics^ v. 2; Physics^ n. 3.
4i6
WILLIAM HARVEY
parts— as effects differ, so does it seem probable
that efficients also vary: from things that pro-
duce different operations, different motions
likewise proceed. Thus physicians in their
physiologies assign certain organs as the agents
of chylification, others of sanguification, others
of generation, &c.; and anatomists speak of the
ossific, carnific, and neurific faculties, which
they conceive produce bones, flesh, and nerves.
But in the generation of the chick, of several
actions differing not a little from one another, it
is certain that the efficient causes must also dif-
fer; those that present themselves to us as ac-
cidental efficients of generation must neverthe-
less be necessary, seeing, that unless they are as-
sociated or intervene, nothing is effected; those,
to wit, are rightly held "efficients" which,
whilst they remove external hinderances, ei-
ther cherish the conception, or stimulate and
turn mere potentiality into positive action. Un-
der this head we should arrange incubation, the
proper temperature of the air and the place,
the spring season, the approach of the sun in
the circle of the zodiac; in like manner the pre-
paring causes which lead the vitellus to rise,
make the macula to dilate, and the fluids in the
egg to liquefy, are all properly held "efficients.**
Further, to the number of efficient causes are
to be reckoned the generative and architec-
tonic faculties, styled parts by Fabricius, viz.,
the immutative, the concoctive, the formative,
the augmentative, as also the effective causes of
certain accidentals, viz., that which constitutes
the pullet male or female, like the father or
the mother, taking after the form of the first
or last male having connexion with the mother;
that too whence the offspring is an animal;
whether perfect or defective; robust and
healthy, or diseased; longer or shorter lived;
keeping up the characters of the race or degen-
erating from them; a monster, an hybrid, &c.
Lastly, when we were discussing the efficient
causes of the foetus, we were not inattentive to
its admirable structure, to the functions and
uses of all its parts and members; neither did
we overlook the foresight, the art, the intelli-
gence, the divine inspiration with which all
things were ordained and skilfully continued
for the ends of life. It is not enough that we in-
quire what is the "efficient," the architect, the
adviser, but that we likewise venerate and
adore the omnipotent Creator and preserver of
a work, which has been well entitled a micro-
cosm. We also ask whence this divine some-
thing comes, when it arrives, and where it re-
sides in the egg; this something which is anal-
ogous to. the essence of the stars, and is near
akin to art and intelligence, and the vicar of the
Almighty Creator?
From what precedes it will be apparent how
difficult it were to enumerate all the efficient
causes of the chick; it is indispensable, indeed,
in the complete investigation of this subject to
refer to a general disquisition; we could not
from the single generation of the chick in ovo,
and without clearer light derived from investi-
gations extended to other animals, venture on
conclusions that should be applicable to the
whole animal creation. And this all the more,
since Aristotle himself has enumerated such a
variety of efficient principles of animals; for he
at one time adduces the "male"1 as the prin-
cipal efficient cause, as that, to wit, in which the
reason of the engendered chick resides, accord-
ing to the axiom: "all things are made by the
same 'univocal* ";2 at another time he takes
"the male semen";8 or, "the nature of the male
emitting semen";4 sometimes it is "that which
inheres in the semen, which causes seeds to be
prolific, spirit, to wit, and nature in that spirit
corresponding in its qualities to the essence of
the stars";5 elsewhere he says it is "heat";6
"moderate heat**;7 "a certain and proportion-
ate degree of heat**;8 "the heat in the blood'*;9
"the heat of the ambient air**; "the winds*';10
"the sun*'; "the heavens'*; "Jupiter**; "the
soul**; and, somewhere, nature is spoken of by
him as "the principle of motion and rest.*'
Aristotle concludes the discussion on the
efficient cause by declaring it "extremely doubt-
ful" whether it be "anything extrinsic; or
something inherent in the geniture or semen;
and whether it be any part of the soul, or the
soul itself, or something having a soul?'*11
To escape from such a labyrinth of "efficient
causes,** it were necessary to be furnished with
Ariadne's thread, composed from observations
on almost every animal that lives; on this ac-
count the subject is deferred till we come to our
more general disquisition. Meantime we shall
recount the particulars which either manifestly
appear in the special history of the chick from
1 Metaphysics, i. 2; iv. i.
2 Ibid., vn. 10.
8 On the Parts of Animals, i. i.
4 On the Generation of Animals, i. 20.
6 Ibid., ii. 3.
9 Ibid., v. 3.
* Ibid., iv 2.
*Ibid., iv. 4.
9 On the Parts of Animals, n. 2.
10 On the Generation of Animals, iv. 2; History of
Animals, vi. 19.
u On the Generation of Animals, n. i.
ANIMAL GENERATION
the egg, or which differ from the ideas usually
entertained, or that seem to demand further
inquiry.
EXERCISE 47. Of the manner in which the efficient
cause of the chicly acts, according to Aristotle
It is universally allowed, that the male is the
primary efficient cause in generation, on the
ground that in him the species or form resides;
and it is further affirmed, that the emission of
his "geniture" during coition, is the cause both
of the existence and the fertility of the egg.
But none of the philosophers nor physicians,
ancient or modern, have sufficiently explained
in what manner the seed of the cock produced
a chick from the egg; nor have they solved the
question proposed by Aristotle. Nor, indeed, is
Aristotle himself much more explanatory , when
he says "that the male contributes not in re-
spect of quantity, but of quality, and is the
origin of action; but that it is the female which
brings the material." And a little after, "It is
not every male that emits seed, and in those
which do so, this is no part of the foetus; just as
in the case of a carpenter, nothing is translated
from him to the substance of the wood which he
uses, nor does any part of the artist's skill reside
in the work when completed; but a form and
appearance arc given by his operation to the
matter; and the soul, which originates the idea
of forms, and the skill to imitate them, moves
the hands, or other limb, whatever it may be,
by a motion of a certain quality; or from diver-
sity proceeds difference; or from similarity pro-
ceeds resemblance. But the hands and instru-
ments move the material. So the nature of a
male, which emits semen, uses that semen as an
instrument, and an act having motion; as in
works of art the instruments are moved, for in
them, in some sort, the motion of the art
exists."
By these words he seems to imply that gener-
ation is owing to the motion of a certain quality.
Just as in art, though the first cause (the ratio
operis) be in the mind of the artist, yet after-
wards, the work is effected by the movement of
the hands or other instruments; and although
the first cause be removed (as in automatons),
yet is it in some sort said to move what it now
does not touch, but once has touched, so long as
motion continues in the instrument.
Also in the next book, he says: "When the
semen of the male has arrived as far as the uterus
of the female, it arranges and coagulates the
purest part of the excrement (meaning the
menstrual blood existing in the uterus); and,
by a motion of this kind, changes the material,
which has been prepared in the uterus, till it
forms part of the chick; and this, hereafter,
although the semen after the performance of
this motion disappears, exists as part of the foe-
tus, and becomes animate (as the heart) and
regulates its own powers and growth, as a son
emancipated from his father, and having his
own establishment. And so it is necessary that
there be some commencing principle, from'
which afterwards the order of the limbs may be
delineated, and a proper disposition made of
those things that concern the absolution of the
animal; a principle, which may be the source of
growth and motion to all the other parts; the
origin of all, both similar and dissimilar parts,
and the source of their ultimate aliment. For
that which is already an animal grows, but the
ultimate aliment of an animal is the blood, or
something corresponding to the blood, whose
vessels and receptacles are the veins; wherefore,
the heart is the origin of the veins. But veins,
like roots, spread to the uterus, and through
these the foetus derives its nourishment. The
heart too, being the beginning of all nature and
the containing end, ought to be made first; as
if it were a genital part by its own nature, which,
as the original of all the other parts, and of the
whole animal, and of sense, must needs be the
first; and by its heat (since all the parts are in
the mate rial potentially), when once the begin-
ning of the motion has taken place, all that fol-
lows is excited, just as in spontaneous miracles;
and the parts are commenced, not by change of
place, but by alteration in softness, hardness,
temperature, and the other differences observed
in similar parts, these being now actually made,
which had before existed only potentially."
This is, in nearly so many words, the opinion
of Aristotle, which supposes that the foetus is
formed from the seed by motion, although it is
not at present in communication with the foe-
tus, but simply has been so at a former time: his
reasonings are, indeed, ingenious, and carefully
put together, and from what we see in the order
of the generation of parts, not improbable. For
the heart, with the channel of the veins, is first
noticed as an animate principle, in which mo-
tion and sense reside; or, as it were, an emanci-
pated son, and a genital part, whence the order
of the members is delineated, whence all things
pertaining to the completion of the animal are
disposed, and which has all the attributes be-
stowed upon it by Aristotle.
But it seems impossible that the heart should
be formed in the egg by the seed of the male,
4i8
WILLIAM HARVEY
when that seed neither exists in the egg, nor
touches it, nor ever has touched it; because the
seed does not enter the uterus where the egg is
(as is allowed by Fabricius), nor is in any way
attracted by it; nay, even the maternal blood
is not in the egg, nor any other prepared mat-
ter, out of which the seed of the male may form
this genital part, the author of all the others.
For it is not immediately after coition, while
the seed still remains within the body, and is
in communication, that any part of the chick
exists in the egg, but after many days, when in-
cubation has taken place. Moreover, in fishes,
when the geniture of the male does nothing but
touch the eggs externally, and does not enter
into them, it is not likely that it performs any
more ample functions when the agency is ex-
ternal, than does the seed of the cock in the
already formed eggs of the hen. Besides, since
immediately after coition no trace of the egg as
yet exists, but it is afterwards generated by the
hen herself (I am speaking of the prolific egg) ;
when now the seed of the cock is departed and
vanished, there is no probability that the foetus
is formed in that egg by the aforesaid seed,
through means of one or any number of suc-
cessive motions.
Nor indeed does the difference between pro-
lific and unprolilic or wind eggs consist herein,
that the former contained the seed of the male,
as Aldrovandus supposed; nor has it been no-
ticed that anything has been formed and coagu-
lated in the egg by the seed of the male, nor has
any sensible transmutation been discovered (for
indeed, there is no sensible difference between
the fertile and the wind egg) ; and yet a prolific
egg, conceived long after coition, has in itself
the faculties of both sexes; viz., the capability
of being both formed itself, and of forming a
chick; as if, according to the idea of Aristotle, it
had derived its origin from the coition of the
two, and their mutual endeavours towards the
same end; and compelled by the force of this
argument, as mentioned above, when speaking
of the generation of the ovum, he has endowed
the egg with a vital principle (anima). If such
really exist, then, without doubt it would be
the origin and efficient of all the natural phe-
nomena which take place in the egg. For if we
consider the structure of the chick, displaying,
as it does, so much art, so divine an intelligence
and foresight; when we see the eyes adapted for
vision, the bill for taking food, the feet for
walking, the wings for flying, and similarly the
rest of its parts, each to its own end, we must
conclude, whatever the power be which cre-
ates such an animal out of an egg, that it is
either the soul, or part of the soul, or something
having a soul, or something existing previous to,
and more excellent than the soul, operating
with intelligence and foresight.
From the generation of the chick, it is also
manifest that, whatever may have been its
principle of life or first vegetative cause, this
cause itself first existed in the heart. Now, if
this be the soul of the chicken, it is equally clear
that that soul must have existed in the punctum
saliens and the blood; since we there discover
motion and sense; for the heart moves and leaps
like an animal. But if a soul exists in the punc-
tum saliens, forming, nourishing, and augment-
ing the rest of the body, in the manner which
we have pointed out in our history, then it,
without doubt, flows from the heart, as from a
fountain-head, into the whole body. Likewise,
if the existence of the vital principle (anima) in
the egg, or, as Aristotle supposes, if the vege-
tative part of the soul be the cause of its fer-
tility, it must follow that the punctum saliens,
or animate genital part, proceeds from the vital
principle (anima) of the egg (for nothing is its
own author), and that the said vital principle
(anima) passes from the egg into the punctum
saliens, presently into the heart, and thence in-
to the chick.
Moreover, if the egg have a prolific virtue,
and a vegetative soul, by which the chick is
constructed, and if it owe them, as is allowed on
all hands, to the semen of the cock; it is clear
that this semen is also endowed with an active
principle (anima). For such is Aristotle's opin-
ion, when he expresses himself as follows: "As
to whether the semen has a vital principle (ant-
ma) or not, the same reasoning must be adduced
which we have employed in the consideration
of other parts. For no active principle (anima)
can exist, except in that thing whose vital prin-
ciple it is; nor can there be any part which is
not partaker of the vital principle, except it be
equivocally, as the eye of a dead man. We must,
therefore, allow, both that the semen has an ac-
tive principle (anima) and is potential."
Now from these premises, it follows that the
male is the primary efficient in which the ratio
and forma reside, which produces a seed or
rather a prolific geniture, and imparts it, im-
bued as it is with an anima vegetativa (with
which also the rest of its parts are endowed) to
the female. The introduction of this geniture
begets such a movement in the material of the
hen, that the production of an animate egg is
the result, and from thence too the first particle
ANIMAL GENERATION
419
of the chick is animated, and afterwards the
whole chick. And so, according to Aristotle,
either the same soul passes, by means of some
metempsychosis, from the cock into his geni-
ture, from the geniture into the material of the
female, thence into the egg, and from the egg
into the chick; or else, it is raised up in each of
the subsequent things by its respective ante-
cedent; namely, in the seed of the male by the
male himself, in the egg by the seed, last in the
chick by the egg, as light is derived from light.
The efficient, therefore, which we look for in
the egg, to explain the birth of the chick, is the
vital principle (anima)', and therefore, the vital
principle of the egg; for, according to Aristotle,
a soul does not exist except in that thing whose
soul it is.
But it is manifest that the seed of the male is
not the efficient of the chick; neither as an in-
strument capable of forming the chick by its
motion, as Aristotle would have it, nor as an
animate substance transferring its vitality (am-
mo) to the chick. For in the egg there is no
semen, neither does any touch it, nor has ever
done so ("and it is impossible that that which
does not touch should move, or that anything
should be affected by that which does not move
it"); and therefore the vitality of the semen
ought not to be said to exist in it; and although
the vital principle may be the efficient in the
egg, yet it would not appear to result more
from the cock or his semen, than from the hen.
Nor, indeed, is it transferred by any metem-
psychosis or translation from the cock and his
semen into the egg, and thence into the chick.
For how can this translation be carried on into
the eggs that are yet to exist, and to be con-
ceived after intercourse P unless either some ani-
mate semen be in the mean time working in
some part of the hen; or the vital principle only
have been translated without the seed, in order
to be infused into any egg which might there-
after be produced; but neither of these alter-
natives is true. For in no part of the hen is the
semen to be found; nor is it possible that the
hen after coition should be possessed of a double
vital principle, to wit, her own, and that of the
future eggs and chicks; since "the living prin-
ciple or soul is said to be nowhere but in that
thing whose soul it is," much less can one or
more vital principles lie hidden in the hen, to
be afterwards subservient to the future eggs
and chicks in their order, as they are produced.
We have adduced these passages out of Aris-
totle in order to set forth his opinion of the
manner in which the seed of the cock produces
the chick from the egg; and thereby throw at
least some light on this difficult question. But
whereas the said passages do not explain the
mode in which this is accomplished, nor even
solve the doubts proposed by himself, it ap-
pears that we are still sticking in the same mud,
and caught in the same perplexities (concerning
the efficient cause of the foetus in the genera-
tion of animals); indeed, so far from Aristotle's
arguments rendering this question more clear,
they appear on the contrary to involve it in
more and greater doubts.
Wherefore it is no wonder that the most ex-
cellent philosopher was in perplexity on this
head, and that he has admitted so great a vari-
ety of efficient causes, and at one time has been
compelled to resort to automatons, coagula-
tion, art, instruments, and motions, for illustra-
tions; at another time to an "anima" in the egg,
and in the seed of the male. Moreover, when he
seems positively and definitively to determine
what it is in each seed, whether of plants or ani-
mals, which render the same fertile, he repudi-
ates heat and fire as improper agents; nor does
he admit any faculty of a similar quality; nor
can he find anything in the seed which should
be fit for that office; but he is driven to ac-
knowledge something incorporeal, and coming
from foreign sources, which he supposes (like
art, or the mind) to form the foetus with intelli-
gence and foresight, and to institute and ordain
all its parts for its welfare. He takes refuge, I
say, in a thing which is obscure and not recog-
nizable by us; namely, in a spirit contained in
the seed, and in a frothy body, and in the na-
ture in that spirit, corresponding in proportion
to the elements of the stars. But what that is,
he has nowhere informed us.
EXERCISE 48. The opinion of Fabricius on the
efficient cause of the chicly is refuted
As I have chosen Aristotle, the most eminent
among the ancient philosophers, and Fabricius
of Aquapendente, one of the foremost anato-
mists of modern times, as my especial guides
and sources of information on the subject of
animal generation, when I find that I can make
nothing of Aristotle upon a particular topic, I
straightway turn to Fabricius; and now I desire
to know what he thought of the efficient cause
of generation.
I find that he endeavours to satisfy three
doubts or difficulties involved in this subject:
First, What is the "efficient" of the chick? This
he answers, by saying, the semen of the male.
Secondly, How does this appear in the egg, and
420
WILLIAM HARVEY
in what way does the semen of the cock fecun-
date the egg? Thirdly and lastly, In what order
are the parts of the chick engendered ?
As to the first query, it appears from our
observations, that the cock and his seminal fluid
are verily the "efficient," but not the "ade-
quate" cause of generation; that the hen comes
in here as something. In this place, therefore,
we are principally to inquire how the semen of
the cock fecundates the egg otherwise unpro-
lific, and secures the engenderment of a chick
from it ?
But let us hear Fabricius: "Those things dif-
fer," he observes, "that are produced from
eggs, from those that originate from semen, in
this, that oviparous animals have the matter
from which the embryo is incorporated distinct
and separate from the agent; whilst viviparous
animals have the efficient cause and the matter
associate and concorporate. For the 'agent' in
the oviparous animal is the semen of the male,
in the fowl the semen of the cock, which neither
is nor can be in thefegg; the 'matter,' again, is
the chalazae from which the foetus is incorpo-
rated. These two differ widely from one an-
other; for the chalazae are added after the vitel-
lus is formed, whilst it is passing through the
second uterus, and are an accession to the in-
ternal egg; the semen galli, on the contrary, is
stored near the fundament, is separated from
the chalazae by a great interval, and neverthe-
less by its irradiating faculty, fecundates both
the whole egg and the uterus. Now in the vivip-
arous animal, the semen is both 'matter' and
'agent,' the two consisting and being conjoined
in the same body."1
Our author appears to have introduced this
distinction between oviparous and viviparous
animals, that he might spare, or at all events,
that he might not directly shock or upset the
notions of medical writers on the generation of
man, they teaching that the seminal fluids of
either sex, projected together in intercourse,
are mingled; that as one or other preponderates,
this becomes the "efficient," that stands in lieu
of the "matter"; and that the two together,
tending to the same end, amalgamate into the
"conception" of the viviparous animal.
But when he finds that neither in the egg nor
uterus of the fowl is there any semen or blood,
and avows his belief that nothing is emitted by
the male in intercourse, that can by possibility
reach the uterus of the female, nor in the egg
discovers a trace of aught supplied by the male,
he is compelled to doubt how the semen, which
1 Of. cit., p. 38.
is nowhere to be detected, which is neither
mixed with the "geniture" of the female, nor
yet is added to it, nor touches it, can fecundate
the egg, or constitute the chick. And this all
the more urgently, when he has stated that a
few connexions in the beginning of the season
suffice to secure the fecundity of all the eggs
that will be laid in its course. For how should
it seem otherwise than impossible that from the
semen galli communicated in the spring, but
now long vanished, lost or consumed, the eggs
that continue to be laid through the summer
and autumn, should still be rendered fruitful
and fit to produce pullets?
It is that he may meet such a difficulty half
way, that he coins the difference which has been
noticed. By way of bolstering up his views, he
further adduces three additional considerations:
First, since the semen galli is neither extant in
the egg, nor was ever present in the uterus, nor
is added as "material cause" as in viviparous
animals, he has chosen to make it resident for a
whole year in the body of the hen. And then
that he may have a fit receptacle or storehouse
for the fecundating fluid, he finds a blind sac
near the inlet to the uterus, in which he says the
cock deposits his semen, wherein, as in a treas-
ury, it is stored, and from which all the eggs are
fecundated. Lastly, although the semen in that
bursa comes into contact neither with the uter-
us, nor the egg, nor the ovary, whereby it might
fecundate the egg, or secure the generation of a
chick, he says, nevertheless, that from thence, a
certain spiritual substance or irradiation pene-
trates to the egg, fecundates its chalazae, and
from these produces a chick. By this affirma-
tion, however, he appears to support the opin-
ion of Aristotle, namely, that the female sup-
plies the "matter" in generation, the male the
"efficient force"; and to oppose the postulate of
medical writers about the mixture of seminal
fluids, for the sake of which, nevertheless, as I
have said, he seems to have laid down his dis-
tinction between oviparous and viviparous ani-
mals: To give an air of greater likelihood to this
notion of his, he goes on to enumerate the
changes which the semen, not yet emitted, but
laid up in the testes and vesiculae seminales of
animals, occasions.
But besides the fact that all this does not
bear upon the question, for the principal ele-
ment under discussion is, not how the semen
galli renders the egg prolific, but rather, how
does the semen galli fashion and construct the
chick from the egg? Almost everything he
adduces in support of his view appears either
ANIMAL GENERATION
421
false or open to suspicion, as is obvious, from
the facts stated in our history; for neither is the
blind cavity situated at the root of the uro-
pygium or coccyx of the fowl, which he entitles
"bursa," destined as a receptacle for the semen
of the cock, nor can any semen be discovered
there, as we have said; but the cavity is en-
countered in the male as well as in the female
fowl.
Our authority nowhere explains what he
understands by a "spiritual substance," and an
"irradiation"; nor what he means by "a sub-
stance through whose virtue the egg is vivi-
fied": he does not say whether it is any "cor-
poreal" or "formal" substance, which by "irra-
diation" proceeds from the semen laid up in
the bursa, and (what is especially required)
constructs a pullet from the egg.
In my opinion, Fabricius does no more here
than say: "It produces the chick because it irra-
diates the egg; and forms because it vivifies";
he attempts to explain or illustrate the exceed-
ingly obscure subject of the formation of a liv-
ing being by means still more obscure. For the
same doubt remains untouched, how, to wit,
the semen of the cock without contact, an "ex-
ternal efficient" at best, separate in point of
place, and existing in the bursa, can form the
internal parts of the foetus in ovo, the heart,
liver, lungs, intestines, &c., out of the chalazae
by "irradiation." Unless, indeed, our author
will have it that all takes place at the dictum as
it were of a creator seated on his throne, and
speaking the words: Let such things be! name-
ly, bones for support, muscles for motion, spe-
cial organs for sense, members for action, vis-
cera for concoction and the like, and all ordered
for an end and purpose with foresight, and
understanding and art. But Fabricius nowhere
demonstrates that the semen has any such vir-
tue, nowhere explains the manner in which
without so much as contact the semen can effect
such things; particularly when we see that the
egg incubated by a bird of another kind than
that which laid it, or cherished in any other
way, or in dung, or in an oven, far from the
bursa of the parent hen, is still quickened and
made to produce an embryo.
The same difficulty still remains, I say: how
or in what way is the semen of the cock the
"efficient" of the chick? It is in no wise re-
moved by invoking the irradiation of a spiritual
substance. For did we even admit that the
semen was stored in the bursa, and that it in-
corporated the embryo from the chalazae by
metamorphosis and irradiation, we should not
be the less deeply immersed in the difficulty of
accounting for the formation of all the internal
parts of the chick. But these notions have al-
ready been sufficiently refuted by us.
Wherefore, in investigating the efficient cause
of the chick, we must look for it as inhering in
the egg, not as concealed in the bursa; and it
must be such, that although the egg have long
been laid, be miles removed from the hen that
produced it, and be set under another hen than
its parent, even under a bird of a different kind,
such as a turkey or guinea-fowl, or merely
among hot sand or dung, or in an oven con-
structed for the purpose, as is done in Egypt, it
will still cause the egg to produce a creature of
the same species as its parents, like them, both
male and female, and if the parents were of
different kinds, of a hybrid species, and having
a mixed resemblance.
The knot therefore remains untied, neither
Aristotle nor Fabricius having succeeded even
in loosening it, namely : how the semen of the
male or of the cock forms a pullet from an egg,
or is to be termed the "efficient" of the chick,
especially when it is neither present in, nor in
contact with, nor added to the egg. And al-
though almost all assert that the male and his
semen are the efficient cause of the chick, still
it must be admitted, that no one has yet suffi-
ciently explained how it is so, particularly in
our common hen's egg.
EXERCISE 49. The inquiry into the efficient cause
of the chicly is one of great difficulty
The discussion of the efficient cause of the
chick is, as we have said, sufficiently difficult,
and all the more in consequence of the various
titles by which it has been designated. Aristotle,
indeed, recites several efficient causes of ani-
mals, and numerous controversies have arisen
on the subject among writers (these having
been particularly hot between medical authors
and Aristotelians) who have come into the are-
na with various explanations, both of the na-
ture of the efficient cause and of the mode of its
operation.
And indeed the Omnipotent Creator is no-
where more conspicuous in his works, nowhere
is his divinity more loudly proclaimed, than in
the structure of animals. And though all know
and admit that the offspring derives its origin
from male and female, that an egg is engen-
dered by a cock and a hen, and that a pullet
proceeds from an egg, still we are not informed
either by the medical schools or the sagacious
Aristotle, as to the manner in which the cock or
422
WILLIAM HARVEY
his semen fashions the chick from the egg. For
from what we have had occasion to say of the
generation of oviparous and other animals, it is
sufficiently obvious that neither is the opinion
of the medical authorities admissible, who de-
rive generation from the admixture of the semi-
nal fluids of the two sexes, nor that of Aristotle,
who holds the semen masculinum for the effi-
cient, and the menstrual blood for the material
cause of procreation. For neither in the act of
intercourse nor shortly after it, is aught trans-
ferred to the cavity of the uterus, from which
as matter any part of the foetus is immediately
constituted. Neither does the "geniture" pro-
ceeding from the male in the act of union
(whether it be animated or an inanimate in-
strument) enter the uterus; neither is it at-
tracted into this organ; neither is it stored up
within the fowl; but it is either dissipated or
escapes. Neither is there anything contained in
the uterus immediately after intercourse, which,
proceeding from the male, or from the female,
or from both, can be regarded as the matter or
rudiment of the future foetus. Neither is the
semen galli stored and retained in the bursa
Fabricii of the hen or elsewhere, that from
thence, as by the irradiation of some spiritual
substance, or by contact, the egg may be fash-
ioned or the chick constituted from the egg.
Neither has the hen any other semen save papu-
lae, yelks, and eggs. These observations of ours,
therefore, render the subject of generation one
of greater difficulty than ever, inasmuch as all
the presumptions upon which the two old
opinions repose are totally overthrown. The
fact is especial, as we shall afterwards demon-
strate, that all animals are alike engendered
from eggs; and in the act of intercourse, whether
of man or the lower quadrupeds, there is no
seminal fluid, proceeding from the male or the
female, thrown into the uterus or attracted by
this organ; there is nothing to be discovered
within its cavity, either before intercourse,
during the act, or immediately after it, which
can be regarded as the matter of the future
foetus, or as its efficient cause, or as its com-
mencement.
Daniel Sennert, a man of learning and a close
observer of nature, having first passed the rea-
sonings of a host of others under review, ap-
proaches the subject himself; and concludes
that the vital principle inheres in the semen
and is almost identical with that which resides
in the future offspring. So that Sennert does
not hesitate to aver that the rational soul of
man is present in his seminal fluid, and by a
parity of reasoning that the egg possesses the
animating principle of the pullet; that the vital
principle is transported to the uterus of the fe-
male with the semen of the male, and that from
the seminal fluids of either conjoined, not mixed
(for mixture, he says, is applied to things of dif-
ferent species), and endowed with soul or the
vital principle a perfect animal emerges. And
therefore, he says, the semen of either parent is
required, whether to the constitution of the
ovum or of the embryo. And having said so
much, he seems to think that he has overcome
all difficulties, and has delivered a certain and
perspicuous truth.
But in order that we should concede a soul or
vital principle (anima) to the egg, and that
combined from the souls of the parents, these
being occasionally of different species, the horse
and the ass, the common fowl and the pheasant,
for example, this vital principle not being a
mixture but only an union; and allow the pullet
to be produced in the manner of the seeds of
plants, by the same efficient principle by
which the perfect animal is afterwards preserved
through the rest of its life, so that it would be
absurd to say that the foetus grew by one vital
principle without the uterus or ovum, and by
another within the uterus or ovum— did we
grant all this, I say (although it is invalid and
undeserving faith), our history of generation
from the egg, nevertheless, upsets the founda-
tions of the doctrine, and shows it to be entirely
false; namely, that the egg is produced from the
semen of the cock and hen, or that any seminal
fluid from either one or other is carried to the
uterus, or that the embryo or any particle of it
is fashioned from any seminal fluid transported
to the uterus, or that the semen galli, as effi-
cient cause and plastic agent, is anywhere stored
up or reserved within the body of the hen to
serve when attracted into the uterus, as the
matter and nourishment whence the foetus
which it has produced should continue to grow.
The conditions are wanting which he himself
admits, after Aristotle, to be necessary, viz.,
that the embryo be constituted by that which
is actual and pre-exists, and the chick by that
which is present and exists in the place where
the chick is first formed and increases; further,
that it be produced by that which is accom-
plished immediately and conjunctly, and is the
same by which the chick is preserved and grows
through the whole of its life. For the semen
galli (and whether it is viewed as animate or
inanimate is of no moment) is nowise present
and conjunct either in the egg or in the uterus;
ANIMAL GENERATION
4*3
neither in the matter from which the chick is
fashioned, nor yet in the chick itself already
begun, and as contributing either to its forma-
tion or perfection.
He dreams, too, when he seeks illustrations
of his opinions on an animated semen from such
instances as the seeds of plants and acorns; be-
cause he does not perceive the difference alleged
by Aristotle1 between the "geniture" admitted
in intercourse and the first conception engen-
dered by both parents; neither does he observe
on the egg produced originally in the cluster of
the viteliarium, and without any geniture,
whether proceeding from the male or the fe-
male, translated to the uterus. Neither does he
understand that the uterus is, even after inter-
course, completely empty of matter of every
kind, whether transmitted by the parents, or
produced by the intercourse, or transmuted in
any way whatever. Neither had he read, or at
all events he does not refer to the experiment
of Fabricius, namely, that a hen is rendered so
prolific by a few treads of the cock, that she
will continue to lay fruitful eggs for the rest of
the year, although in the interval she receives
no new accessions of semen for the fecundation
of each egg as it is laid, neither does she retain
any of the seminal fluid which she received so
long ago.
So much is certain, and disputed by no one,
that animals, all those at least that proceed
from the intercourse of male and female, are the
offspring of this intercourse, and that they are
procreated as it seems by a kind of contagion,
much in the same way as medical men observe
contagious diseases, such as leprosy, lues venera,
plague, phthisis, to creep through the ranks of
mortal men, and by mere extrinsic contact to
excite diseases similar to themselves in other
bodies; nay, contact is not necessary; a mere
halitus or miasm suffices, and that at a distance
and by an inanimate medium, and with nothing
sensibly altered: that is to say, where the con-
tagion first touches, there it generates an "univ-
ocal" like itself, neither touching nor existing
in fact, neither being present nor conjunct, but
solely because it formerly touched. Such virtue
and efficacy is found in contagions. And the
same thing perchance occurs in the generation
of animals. For the eggs of fishes, which come
spontaneously to their full size extrinsically,
and without any addition of male seminal fluid,
and are therefore indubitably possessed of vi-
tality without it, merely sprinkled and touched
with the milt of the male, produce young fishes.
1 On the Generation of Animals, 11,1.
The semen of the male, I say, is not intromitted
in such wise as to perform the part of "agent"
in each particular egg, or to fashion the body,
or to introduce vitality (anima); the ova are
only fecundated by a kind of contagion. Whence
Aristotle calls the milt of the male fish, or the
genital fluid diffused in water, at one time "the
genital and fcetific fluid," at another, "the vital
For he says: "The male fish sprinkles
virus.
the ova with his genital semen, and from the
ova that are touched by this vital virus young
fishes are engendered."2
Let it then be admitted as matter of certainty
that the embryo is produced by contagion. But
a great difficulty immediately arises, when we
ask: how, in what way is this contagion the
author of so great a work ? By what condition
do parents through it engender offspring like
themselves, or how does the semen masculinum
produce an "univocal" like the male whence it
flowed? When it disappears after the contact,
and is naught in act ulteriorly, either by virtue
of contact or presence, but is corrupt and has
become a nonentity, how, I ask, does a non-
entity act? How does a thing which is not in
contact fashion another thing like itself? How
does a thing which is dead itself impart life to
something else, and that only because at a
former period it was in contact?
For the reasoning of Aristotle appears to be
false, or at all events defective, where he con-
tends "That generation cannot take place with-
out an active and a passive principle; and that
those things can neither act nor prove passive
which do not touch; but that those things come
into mutual contact which, whilst they are of
different sizes, and are in different places, have
their extremes together."3
But when it clearly appears that contagion
from noncontingents, and things not having
their extremities together, produce ill effects
on animals, wherefore should not the same law
avail in respect of their life and generation?
There is an "efficient" in the egg which, by its
plastic virtue (for the male has only touched
though he no longer touches, nor are there any
extremes together), produces and fashions the
foetus in its kind and likeness. And through so
many media or instruments is this power, the
agent of fecundity, transmitted or required that
neither by any movement of instruments as in
works of art, nor by the instance of the autom-
aton quoted by Aristotle, nor of our clocks,
nor of the kingdom in which the mandate of
2 History of Animals ', vi, 13.
* On Generation and Corruption, I, 6.
424
WILLIAM HARVEY
the sovereign is everywhere of avail, nor yet by
the introduction of a vital principle or soul into
the semen w "geniture," can the aforemen-
tioned doctrine be defended.
And hence have arisen all the controversies
and problems concerning the attraction of the
magnet and of amber; on sympathy and antip-
athy; on poisons and the contagion of pesti-
lential diseases; on alexipharmics and medicines
which prove curative or injurious through some
hidden or rather unknown property, all of
which seem to come into play independently of
contact. And above all on what it is in genera-
tion which, in virtue of a momentary contact-
nay, not even of contact, save through several
media — forms the parts of the chick from the
egg by epigenesis in a certain order, and pro-
duces an "univocal" and like itself, and that en-
tirely because it was in contact at a former pe-
riod. How, I ask again, does that which is not
present, and which only enjoyed extrinsic con-
tact, come to constitute and order all the mem-
bers of the chick in the egg exposed without
the body of the parent, and often at a long in-
terval after it is laid ? how does it confer life or
soul, and a species compounded of those of the
concurring generants ? Inasmuch as nothing, it
seems, can reproduce itself in another's likeness.
EXERCISE 50. Of the efficient cause of animals,
and its conditions
That we may proceed in our subject, there-
fore, and penetrate so far into the knowledge of
the efficient cause of animal generation as seems
needful in this place, we must begin by observ-
ing what instruments or media are devoted to
it. And here we come at once to the distinction
into male and female; seminal fluid and ovum,
and its primordium. For some males, as well as
some females, are barren, or but little prolific;
and the seed of the male is at one time more, at
another time less prolific; because the semen
masculinum stored up in the vesiculae seminales
is esteemed unfruitful, unless it is raised into
froth by the spirits and ejected with force. And
even then perchance it is not endowed with
equal fecundating force at all times. Neither are
all the germs of yelks in the ovary, nor all the
eggs in the uterus made fertile at the same
instant.
Now I call that fruitful which, unless im-
peded by some extrinsic cause, attains by its
inherent force to its destined end, and brings
about the consequence for the sake of which it
is ordained. Thus the cock is called fruitful
which has his hens more frequently and surely
pregnant, the eggs they lay being at the same
time perfect and proper for incubation.
The hen in like manner is esteemed fruitful
which has the faculty of producing eggs, or of
receiving and long retaining the virtue of pro-
lific conception from the cock. The cluster of
germs and the ovary itself are regarded as pro-
lific when the germs are numerous and of good
size.
The egg in the same way is fruitful which dif-
fers from a subventaneous or hypenemic egg,
and which, cherished by incubation, or in any
other way, does not fail to produce a chick.
Such an efficient cause consequently is re-
quired for the chick, as shall impart the virtue
of fecundity to it, and secure it the power of
acting as an efficient cause in its turn. Because
that, or its analogue at least, by means of which
they become prolific, is present in all animals.
And the inquiry is the same in each case, when
we ask what it is in the egg which renders it
prolific, and distinguishes it from a wind egg;
what in the vitellary germ and ovary; what in
the female; what, finally, in the semen and the
cock himself? What, moreover, it is in the
blood and punctum saliens, or first formed par-
ticle of the chick, whence all the other parts
arise with their appropriate structures and ar-
rangements; what in the embryo or chick itself
whereby it becomes more or less robust and
agile, attains to maturity with greater or less
rapidity, and lives with various degrees of
health, for a longer or shorter period ?
Nor is the inquiry very different which goes
to ascertain what sex the male and the female,
or the cock and the hen, confer upon the pro-
lific egg; and what proceeds from each that con-
tributes to the perfection or resemblance of the
chick, viz., whether the egg, the conception,
the matter, and the nutriment proceed from
the mother, and the plastic virtue from the
father; or rather a certain contagion immitted
during intercourse, or produced and received
from him, which in the body of the hen, or in
the eggs, either permanently excites the matter
of the eggs, or attracts nourishment from the
female, and concocts and distributes it first for
the growth of the eggs, and then for the pro-
duction of the chicks; finally, whether from the
male proceeds all that has reference to form and
life and fecundity, from the female, again, all
that is of matter, constitution, place, and nour-
ishment? For among animals where the sexes
are distinct, matters are so arranged, that since
the female alone is inadequate to engender an
embryo and to nourish and protect the young,
ANIMAL GENERATION
425
a male is associated with her by nature, as the
superior and more worthy progenitor, as the
consort of her labour, and the means of supply-
ing her deficiencies; in the case of the hen, of
correcting by his contagion the inferiority of
the hypenemic eggs which she produces, and
so rendering them prolific. For as the pullet,
engendered of an egg, is indebted to that egg
for his body, vitality, and principal or gener-
ative part, so and in like manner does the egg
receive all that is in it from the female, the fe-
male in her turn being dependent on the male
for her fecundity which is conferred in coition.
And here we have an opportunity of inquir-
ing, whether the male be the first and principal
cause of the generation of the offspring; or
whether the male along with the female are the
mediate and instrumental causes of nature it-
self, or of the first and supreme generator? And
such an inquiry is both becoming and neces-
sary, for perfect science of every kind depends
on a knowledge of causes. To the full under-
standing of generation, therefore, it is incum-
bent on us to mount from the final to the first
and supreme efficient cause, and to hold each
and every cause in especial regard.
We shall have occasion to define that which
is the first and supreme efficient cause of the
chick in ovo by and by, when we treat of that
which constitutes the efficient cause among ani-
mals in general. Here, meantime, we shall see
what its nature may be.
The first condition, then, of the primary
efficient cause of generation, properly so called,
is, as we have said, that it be the prime and prin-
cipal fertilizer, whence all mediate causes re-
ceive the fecundity imparted. For example, the
chick is derived from the punctum saliens in
the egg, not only as regards the body, but also,
and this especially, as respects the life (anima) :
the punctum saliens, or heart, is derived from
the egg, the egg from the hen, and the hen has
her fecundity from the cock.
Another condition of the prime efficient is
discovered from the work achieved, viz., the
chick, because that is the prime efficient in
which the reason of the effect is principally dis-
played. But since every generative efficient en-
genders another like itself, and the offspring is
of a mixed nature, the prime efficient must also
be a certain mixed something.
Now, I maintain that the offspring is of a
mixed nature, inasmuch as a mixture of both
parents appears plainly in it, in the form and
lineaments, and each particular part of its body,
in its colour, mother-marks, disposition to dis-
eases, and other accidents. In mental constitu-
tion, also, and its manifestations, such as man-
ners, docility, voice, and gait, a similar tem-
perament is discoverable. For as we say of a
certain mixture, that it is composed of ele-
ments, because their qualities or virtues, such
as heat, cold, dryness, and moisture, are there
discovered associated in a certain similar com-
pound body, so, in like manner, the work of the
father and mother is to be discerned both in the
body and mental character of the offspring,
and in all else that follows or accompanies tem-
perament. In the mule, for instance, the body
and disposition, the temper and voice, of both
parents (of the horse and the ass, e. g.) are min-
gled; and so, also, in the hybrid between the
pheasant and the fowl, in that between the wolf
and the dog, &c., corresponding traits are con-
spicuous.
When, therefore, the chick shows his resem-
blance to both parents, and is a mixed effect,
the primary genital cause (which it resembles)
must needs be mixed. Wherefore that which
fashions the chick in the egg is of a mixed na-
ture, a certain something mixed or compounded,
and the work of both parents. And if any kind
of contagion, engendered under the influence
of sexual intercourse, in which the male and fe-
male mingle and form but one body, either
originates or remains in the body of the female,
that, too, must be of a mixed nature or power,
whence, subsequently, a fertile egg will be pro-
duced, endowed with plastic powers, the con-
sequence of a mixed nature, or of a mixed effi-
cient instrument, from which a chick, also of a
mixed nature, will be produced.
I have used the word contagion above, be-
cause Aristotle's view is contradicted by all ex-
perience, viz., that a certain part of the embryo
is immediately made by intercourse. Neither is
it true, as some of the moderns assert, that the
vital principle (anima) of the future chick is
present in the egg; for that cannot be the vital
principle of the chick which inheres in no part
of its body. Neither can the living principle be
said either to be left or to be originated by in-
tercourse; otherwise in every pregnant woman
there would be two vital principles (animas)
present. Wherefore, until it shall have been de-
termined what the efficient cause of the egg is,
what it is of mixed nature that must remain
immediately upon intercourse, we may be per-
mitted to speak of it under the title of a con-
tagion.
But where this contagion lies hid in the fe-
male after intercourse, and how it is communi-
426
WILLIAM HARVEY
cated and given to the egg, demands quite a
special inquiry, and we shall have occasion to
treat of the matter when we come to discuss
the conception of females in general. It will suf-
fice, meantime, if we say that the same law ap-
plies to the prime efficient — in which inheres
the reason of the future offspring — as to the
offspring; as this is of a mixed nature, the na-
ture of its cause must also be mixed; and it must
either proceed equally from both parents, or
from something else which is employed by both
concurrently as instruments, animated, co-oper-
ating, mixed, and in the sexual act coalescing
unto one. And this is the third condition of the
prime efficient, that it either imparts motion to
all the intermediate instruments in succession,
or uses them in some other way, but comes not
itself into play. Whence the origin of the doubt
that has arisen, whether, in the generation of
the chick, the cock were the true prime effi-
cient, or whether there were not another prior,
superior to him ? For, indeed, all things seem to
derive their origin from a celestial influence, and
to follow the movements of the sun and moon.
But we shall be able to speak more positively of
this matter after we have shown what we under-
stand by the "instrument," or "instrumental
efficient cause," and how it is subdivided.
Instrumental efficients, then, are of different
kinds: some, according to Aristotle, are factive,
others active; some have no capacity any way
unless conjoined with another prior efficient, as
the hand, foot, genital organs, &c. with the rest
of the body ; others have an influence even when
separate and distinct, as the seminal fluid and
the ovum. Some instruments, again, have neither
motion nor action beyond those that are im-
parted to them by the prime efficient; and
others have peculiar inherent principles of ac-
tion, to which Nature indeed allows no motion
in the business of generation, though she still
uses their faculties, and prescribes them laws or
limits in their operations, not otherwise than
the cook makes use of fire in cooking, and the
physician of herbs and drugs in curing diseases.
Sennert, that he may uphold the opinion he
had espoused of the vital principle (animd)
being present in the semen, and the formative
faculty of the chick being extant in the egg, as-
serts that not only is the egg, but the semen of
the cock, endowed with the living principle of
the future chick. Moreover, he distinctly de-
nies that there is any separate instrumental effi-
cient; and says, that that only ought to be en-
titled "instrument" which is conjoined with
the prime efficient; and that only "instrumen-
tal efficient," which has no motion or action
save that which is imparted to it by the prime
efficient, or which is continuously and succes-
sively received, and in virtue of which it acts.
And on this ground he rejects the example of
projectiles, which have received force from the
projecting agent, and, separated from it, act
nevertheless; as if swords and spears were prop-
erly to be called warlike weapons, but arrows
and bullets to be refused this title. He also re-
jects the argument derived from the republic,
denying thereby that magistrates, counsellors,
or ministers, are instruments of government;
although Aristotle regards a counsel as an effi-
cient, and in express terms calls a minister an
instrument.1 Sennert likewise denies the ex-
ample of automata; and says and gainsays much
besides, with a view to confirming himself in
his position, that the semen and the egg are
possessed of a living principle (animd), and are
not mediate or instrumental, but principal
agents. Sennert, nevertheless, as it were com-
pelled by the force of truth, lays down such
conditions for a principal agent, as fully and
effectually contradict all that he had said be-
fore. He tells us, for instance, that "whatever
produces a work or an effect more noble than
itself, or an effect unlike itself, is not a principal
efficient, but an instrumental cause"; granting
which, who would not infer that the semen and
the egg were instruments ? seeing that the pul-
let is an effect more noble than the egg, and
every way unlike either this or the spermatic
fluid. Wherefore, when the learned Sennert de-
nies the semen and the egg to be instruments or
organs, because they are distinct from the prime
agents, he takes his position upon a false basis;
because, as the prime generator procreates off-
spring by various means or media, the medium
being here conjunct, as the hand of the work-
man is with his body, there separate and dis-
tinct, as is the arrow let loose from the bow, it
is still to be regarded as an instrument.
From the conditions now enumerated of an
instrumental cause, it seems to follow that the
prime efficient in the generation of the chick is
the cock, or, at all events, the cock and hen,
because the resulting pullet resembles these;
nor can it be held more noble than they, which
are its prime efficients or parents. I shall, there-
fore, add another condition of the prime effi-
cient, whence it may, perhaps, appear that the
male is not the prime, but only the instrumen-
tal, cause of the chick; viz., that the prime effi-
cient in the formation of the chick makes use of
1 Politic^ i. 4.
ANIMAL GENERATION
427
artifice, and foresight, and wisdom, and good-
ness, and intelligence, which far surpass the
powers of our rational soul to comprehend, in-
asmuch as all things are disposed and perfected
in harmony with the purpose of the future
work, and that there be action to a determinate
end; so that every, even the smallest, part of
the chick is fashioned for the sake of a special
use and end, and with respect not merely to the
rearing of the fabric, but also to its well-being,
and elegance and preservation. But the male or
his semen is not such either in the act of kind
or after it, that art, intelligence, and foresight
can be ascribed to him or it.
The proper inference from these premises
appears to be that the male, as well as his semi-
nal fluid is the efficient instrument; and the fe-
male not less than the egg she lays the same.
Wherefore, we have to seek refuge in a prior,
superior, and more excellent cause, to which,
with all propriety, are ascribed foresight, in-
telligence, goodness, and skill, and which is by
so much more excellent than its effect or work,
as the architect is more worthy than the pile he
rears, as the king is more exalted than his min-
ister, as the workman is better than his hands
or tools.
The male and female, therefore, will come to
be regarded as merely the efficient instruments,
subservient in all respects to the Supreme Cre-
ator, or Father of all things. In this sense, con-
sequently, it is well said that the sun and moon
engender man; because, with the advent and
secession of the sun, come spring and autumn,
seasons which mostly correspond with the gen-
eration and decay of animated beings. So that
the great leader in philosophy says: "The first
motion is not the cause of generation and de-
struction; it is the motion of the ecliptic that
is so, this being both continuous and having
two movements; for, if future generation and
corruption are to be eternal, it is necessary that
something likewise move eternally, that inter-
changes do not fail, that of the two actions one
only do not occur. The cause of the perpetuity
is, therefore, the law of the universe; and the
obliquity is the cause of the approach and acces-
sion, and of his being now nearer, now more re-
mote: when he quits us, and removes to a dis-
tance, it is then that decay and corruption inter-
vene; and, in like manner, when he approaches,
it is then that he engenders; and if, as he fre-
quently approaches, he engenders; so, because he
frequently recedes, does he cause corruption; for
the causes of contraries are contrary.*'1
1 On Generation and Corruption, n. 10.
All things, therefore, grow and flourish in
spring (on the approach of the sun, that is to
say, he being the common parent and producer,
or at all events the immediate and universal in-
strument of the Creator in the work of repro-
duction); and this is true not of plants only but
of animals also; nor less of those that come
spontaneously, than of those that are propa-
gated by the consentient act of male and fe-
male. It is as if, with the advent of this glorious
luminary, Venus the bountiful descended from
heaven, waited on by Cupid and a cohort of
graces, and prompted all living things by the
bland incitement of love to secure the perpetu-
ity of their kinds. Or (and it is thus that we
have it in the mythology) it is as if the genital
organs of Saturn, cast into the sea at this season,
raised a foam, whence sprung Aphrodite. For,
in the generation of animals, as the poet says,
"superat tencr omnibus humor"— a gentle mois-
ture all pervades — and the genitals froth and
are replete with semen.
The cock and the hen are especially fertile in
the spring; as if the sun, or heaven, or nature,
or the soul of the world, or the omnipotent
God — for all these names signify the same thing
— were a cause in generation superior and more
divine than they; and thus it is that the sun
and man, i.e., the sun through man as the in-
strument, engenders man. In the same way the
preserver of all things, and the male among
birds, give birth to the egg, from whence the
chick, the perfect bird, is made eternal in its
kind by the approach and recession of the god
of day, who, by the Divine will and pleasure,
or by fate, serves for the generation of all that
lives.
Let us conclude, therefore, that the male,
although a prior and more excellent efficient
than the female, is still no more than an instru-
mental efficient, and that he, not less than the
female, must refer his fecundity or faculty of
engendering as received from the approaching
sun; and, consequently, that the skill and fore-
sight, which are apparent in his work, are not to
be held as proceeding from him but from God;
inasmuch as the male in the act of kind neither
uses counsel nor understanding; neither does
man engender the rational part of his soul,
but only the vegetative faculty; which is not
regarded as any principal or more divine faculty
of the soul, but one only of a lower order.
Since, then, there is not less of skill and pre-
science manifested in the structure of the chick
than in the creation of man and the universe at
large, it is imperative even in the generation of
428
WILLIAM HARVEY
man to admit an efficient cause, superior to,
and more excellent than man himself: other-
wise the vegetative faculty, or that part of the
soul or living principle which fashions and pre-
serves a man, would have to be accounted far
more excellent and divine, and held to bear a
closer resemblance to God than the rational
portion of the soul, whose excellence, neverthe-
less, we extol over all the faculties of all ani-
mals, and esteem as that which has right and
empire in them, and to which all created things
are made subservient. Or we should else have
to own that in the works of nature there was
neither prudence, nor art, nor understanding;
but that these appeared to us, who are wont to
judge of the divine things of nature after our
own poor arts and faculties, or to contrast them
with examples due to ourselves; as if the active
principles of nature produced their effects in
the same way as we are used to produce our
artificial works, by counsel, to wit, or discipline
acquired through the mind or understanding.
But nature, the principle of motion and rest
in all things in which it inheres, and the vege-
tative soul, the prime efficient cause of all gen-
eration, move by no acquired faculty which
might be designated by the title of skill or fore-
sight, as in our undertakings; but operate in
conformity with determinate laws like fate or
special commandments— in the same way and
manner as light things rise and heavy things de-
scend. The vegetative faculty of parents, to
wit, engenders in the same way, and the semen
finally arrives at the form of the foetus, as the
spider weaves her web, as birds build nests, in-
cubate their eggs, and cherish their young, or
as bees and ants construct dwellings, and lay up
stores for their future wants; all of which is
done naturally and from a connate genius or
disposition; by no means from forecast, instruc-
tion, or reason. That which in us is the prin-
ciple or cause of artificial operations, and is
called art, intellect, or foresight, in the natural
operations of the lower animals is nature, which
is duToSiScucros, self-taught, instilled by no
one; what in them is innate or connate, is with
us acquired. On this account it is, that they
who refer all to art and artifice are to be held
indifferent judges of nature or natural things;
and, indeed, it is wiser to act in the opposite
way, and selecting standards in nature to judge
of things made by art according to them. For
all the arts are but imitations of nature in one
way or another; as our reason or understanding
is a derivative from the Divine intelligence,
manifested in his works; and when perfected by
habit, like another adventitious and acquired
soul, gaining some semblance of the Supreme
and Divine agent, it produces somewhat simi-
lar effects.
Wherefore, according to my opinion, he takes
the right and pious view of the matter, who de-
rives all generation from the same eternal and
omnipotent Deity, on whose nod the universe
itself depends. Nor do I think that we are great-
ly to dispute about the name by which this first
agent is to be called or worshipped; whether it
be God, Nature, or the Soul of the universe —
whatever the name employed— all still intend
by it that which is the beginning and the end of
all things; which exists from eternity and is al-
mighty; which is author or creator, and, by
means of changing generations, the preserver
and perpetuator of the fleeting things of mortal
life; which is omnipresent, not less in the single
and several operations of natural things, than
in the infinite universe; which, by his deity or
providence, his art and mind divine, engenders
all things, whether they arise spontaneously
without any adequate efficient, or are the work
of male and female associated together, or of a
single sex, or of other intermediate instruments,
here more numerous, there fewer, whether they
be univocal, or are equivocally or accidentally
produced: all natural bodies are both the work
and the instruments of that Supreme Good,
some of them being mere natural bodies, such
as heat, spirit, air, the temperature of the air,
matters in putrefaction, &c., or they are at
once natural and animated bodies; for he also
makes use of the motions, or forces, or vital
principles of animals in some certain way, to
the perfection of the universe and the procrea-
tion of the several kinds of animated beings.
From what has now been said, we are ap-
prized to a certain extent of the share which
the male has in the business of generation. The
cock confers that upon the egg, which, from
unprolific, makes it prolific, this being identical
with that which the fruit of vegetables receives
from the fervour of the summer sun, which se-
cures to them maturity, and to their seeds fer-
tility; and not different from that which ferti-
lizes things spontaneously engendered, and
brings caterpillars from worms, aurelias from
caterpillars, from aurelias moths, butterflies,
bees, &c.
In this way is the sun, by his approach, both
the beginning of motion and transmutation
in the coming fruit, and the end, also, inasmuch
as he is the author of the fertility of its included
seed: and, as early spring is the prime efficient
ANIMAL GENERATION
429
of leaves and flowers and fruits, so is summer, in
its strength, the cause of final perfection in the
ripeness and fecundity of the seed. With a view
to strengthen this position, I shall add this one
from among a large number of observations.
Some persons in these countries cultivate or-
ange trees with singular care and economy, and
the fruit of these trees, which, in the course of
the first year, will grow to the size of the point
of the thumb, comes to maturity the following
summer. This fruit is perfect in all respects,
save and except that it is without pips or seeds.
Pondering upon this with myself, I thought
that I had here an example of the barren egg,
which is produced by the hen without the con-
currence of the cock, and which comprises
everything that is visible in a fruitful egg, but
is still destitute of germinant seed; as if it were
the same thing that was imparted by the cock,
in virtue of which a wind egg becomes a fruit-
ful egg, which in warmer countries is dispensed
by the sun, and causes tLe fruit of the orange
tree to be produced replete with prolific seed.
It is as if the summer in England sufficed for the
production of the fruit only, as the hen for the
production of the egg, but like the female fowl
was impotent as a pro-genetrix; whilst in other
countries enjoying the sun's light in larger pro-
portion, the summer acquired the characters of
the male, and perfected the work of generation.
Thus far have we treated this subject by the
way, that, from the instance of the egg, we
might learn what conditions were required in
the prime efficient in the generation of animals;
for it is certain that in the egg there is an agent,
as there is also in every conception and germ,
which is not merely infused by the mother,
but is first communicated in coitu by the father,
by means of his spermatic fluid; and which is
itself primarily endowed with such virtue by
heaven and the sun, or the Supreme Creator.
It is equally manifest that this agent, existing
in every egg and seed, is so imbued with the
qualities of the parents, that it builds up the
offspring in their likeness, not in its own; and
this mingled also as proceeding from both united
in copulation. Now, as all this proceeds with
the most consummate foresight and intelligence,
the presence of the Deity therein is clearly
proclaimed.
But we shall have to speak at greater length
upon this subject when we strive to show what
it is that remains with the female immediately
after intercourse, and where it is stored ; at the
same time that we explain — since there is noth-
ing visible in the cavity of the uterus after in-
tercourse— what that prolific contagion or prime
conception is; whether it is corporeal and kid
up within the female, or is incorporeal; whether
the conception of the uterus be of the same na-
ture or not with the conceptions of the brain,
and fecundity be acquired in the same way as
knowledge — a conclusion, in favour of which
there is no lack of arguments; or, as motion and
the animal operations, which we call appetites,
derive their origin from the conceptions of the
brain, may not the natural motions and the
operations of the vegetative principle, and par-
ticularly generation, depend on the conception
of the uterus ? And then we have to inquire how
this prolific contagion is of a mixed nature, and
is imparted by the male to the female, and by
her is transferred to the ovum? Finally, how
the contagious principle of all diseases and pre-
ternatural affections spreads insensibly, and is
propagated ?
EXERCISE 51. Of the order of generation; and,
first) of the primary genital particle
It will be our business, by and by, when we
come to treat of the matter in especial, to show
what happens to the female from a fruitful em-
brace; what it is that remains with her after
this, and which we have still spoken of under
the name of contagion, by which, as by a kind
of infection, she conceives, and an embryo sub-
sequently begins to grow of its own accord.
Meantime, we shall discourse of those things
that manifestly appear in connexion with the
organs of generation which seem most worthy
of particular comment.
And first, since it appears certain that the
chick is produced by epigenesis, or addition of
the parts that successively arise, we shall in-
quire what part is formed first, before any of
the rest appear, and what may be observed of
this and its particular mode of generation.
What Aristotle1 says of the generation of the
more perfect animals, is confirmed and made
manifest by all that passes in the egg, viz.: that
all the parts are not formed at once and to-
gether, but in succession, one after another;
and that there first exists a particular genital
particle, in virtue of which, as from a begin-
ning, all the other parts proceed. As in the seeds
of plants, in beans and acorns, to quote particu-
lar instances, we see the gemmula, or apex, pro-
truding, the commencement of the entire pro-
spective herb or tree. "And this particle is like
a child emancipated, placed independently, a
principle existing of itself, from whence the
1 On the Generation of Animals, ix, i.
430
WILLIAM HARVEY
series of members is subsequently thrown out,
and to which belongs all that is to conduce to
the perfection of the future animal.*'1 Since,
therefore, "No part engenders itself, but, after
it is engendered, concurs in its own growth, it
is indispensable that the part first arise which
contains within itself the principle of increase;
for whether it be a plant or an animal, still has
it within itself the power of vegetation or nutri-
tion";2 and at the same time distinguishes and
fashions each particular part in its several order;
and hence, in this same primogenate particle,
there is a primary vital principle inherent,
which is the author and original of sense and
motion, and every manifestation of life.
That, therefore, is the principal particle
whence vital spirit and native heat accrue to all
other parts, in which the calidum innatum sive
implantatum of physicians first shows itself,
and the household deity or perennial fire is
maintained; whence life proceeds to the body
in general, and to each of its parts in particular;
whence nourishment, growth, aid, and solace
flow; lastly, where life first begins in the being
that is born, and last fails in that which dies.
All this is certainly true as regards the first
engendered part, and appears manifestly in the
formation of the chick from the egg. I am,
therefore, of opinion that we are to reject the
views of certain physicians, indifferent philoso-
phers, who will have it that three principal and
primogenate parts arise together, viz.: the
brain, the heart, and the liver; neither can I
agree with Aristotle himself, who maintains
that the heart is the first engendered and ani-
mated part; for I think that the privilege of
priority belongs to the blood alone; the blood
being that which is first seen of the newly en-
gendered being, not only in the chick in ovo,
but in the embryo of every animal whatsoever,
as shall plainly be made to appear at a later
stage of our inquiry.
There appears at first, I say, a red-coloured
pulsating point or vesicle, with lines or canals
extending from it, containing blood in their
interior, and, in so far as we are enabled to per-
ceive from the most careful examination, the
blood is produced before the punctum saliens
is formed, and is, further, endowed with vital
heat before it is put in motion by a pulse; so
that as pulsation commences in it and from it,
so, in the last struggle of mortal agony, does
motion also end there. I have indeed ascer-
tained by numerous experiments instituted
1 Ibid.
upon the egg, as well as upon other subjects,
that the blood is the element of the body in
which, so long as the vital heat has not entirely
departed, the power of returning to life is con-
tinued.
And since the pulsating vesicle and the san-
guineous tubes extending thence are visible
before anything else, I hold it as consonant with
reason to believe that the blood is prior to its
receptacles, the thing contained, to wit, to its
container, inasmuch as this is made subservient
to that. The vascular ramifications and the
veins, therefore, after these the pulsating vesi-
cle, and, finally, the heart, as being every one
of them organs destined to receive and contain
the blood, are, in all likelihood, constructed for
the express purpose of impelling and distribut-
ing it, and the blood is, consequently, the prin-
cipal portion of the body.
This conclusion is favoured by numerous ob-
servations; particularly by the fact that some
animals, and these red-blooded, too, live for
long periods without any pulse; some even lie
concealed through the whole winter, and yet
escape alive, though their heart had ceased
from motion of every kind, and their lungs no
longer played; they had lain in fact like those
who lie half dead in a state of asphyxia from
syncope, leipothymia, or the hysterical passion.
Emboldened by what I have observed both
in studying the egg, and whilst engaged in the
dissection of living animals, I maintain, against
Aristotle, that the blood is the prime part that
is engendered, and the heart the mere organ
destined for its circulation. The function of the
heart is the propulsion of the blood, as clearly
appears in all animals furnished with red blood;
and the office of the pulsating vesicle in the
generation of the chick a b ovo, as well as in the
embryos of mammiferous animals, is not differ-
ent, a fact which I have repeatedly demon-
strated to others, showing the vesicula pulsans
as a feeble glancing spark, contracting in its
action, now forcing out the blood which was
contained in it, and again relaxing and receiv-
ing a fresh supply.
The supremacy of the blood further appears
from this: that the pulse is derived from it; for,
as there are two parts in a pulsation, viz. : dis-
tension or relaxation, and contraction, or dias-
tole and systole, and, as distension is the prior
of these two motions, it is manifest that this
motion proceeds from the blood; the contrac-
tion, again, from the vesicula pulsans of the
embryo in ovo> from the heart in the pullet, in
virtue of its own fibres, as an instrument des-
ANIMAL GENERATION
tined for this particular end. Certain it is, that
the vesicle in question, as also the auricle of the
heart at a later period, whence the pulsation
begins, is excited to the motion of contraction
by the distending blood. The diastole, I say,
takes place from the blood swelling, as it were,
in consequence of containing an inherent spirit,
so that the opinion of Aristotle in regard to the
pulsation of the heart — namely, that it takes
place by a kind of ebullition — is not without
some mixture of truth; for what we witness
every day in milk heated over the fire, and in
beer that is brisk with fermentation, comes into
play in the pulse of the heart; in which the
blood, swelling with a sort of fermentation, is
alternately distended and repressed; the same
thing that takes place in the liquids mentioned
through an external agent, namely adventitious
heat, is effected in the blood by an intimate
heat, or an innate spirit; and this, too, is regu-
lated in conformity with nature by the vital
principle (ammo), and is continued to the bene-
fit of animated beings,
The pulse, then, is produced by a double
agent: first, the blood undergoes distension or
dilatation, and secondly, the vesicular mem-
brane of the embryo in the egg, the auricles and
ventricles in the extruded chick, effect the con-
striction. By these alternating motions asso-
ciated, is the blood impelled through the whole
body, and the life of animals is thereby con-
tinued,
Nor is the blood to be styled the primogenial
and principal portion of the body, because the
pulse has its commencement in and through it;
but also because animal heat originates in it,
and the vital spirit is associated with it, and it
constitutes the vital principle itself (ipsa ammo) ;
for wheresoever the immediate and principal
instrument of the vegetative faculty is first dis-
covered, there also does it seem likely will the
living principle be found to reside, and thence
take its rise; seeing that the life is inseparable
from spirit and innate heat.
For "however distinct are the artist and the
instrument in things made by art," as Fabricius1
well reminds us, "in the works of nature they
are still conjoined and one. Thus the stomach is
the author and the organ of chylopoesis." In
like manner are the vital principle and its in-
strument immediately conjoined; and so, in
whatever part of the body heat and motion
have their origin, in this also must life take its
rise, in this be last extinguished; and no one, I
presume, will doubt that there are the lares
1 Op. sup. «/., p. 28.
and penates of life enshrined, that there the
vital principle (anima) itself has its seat.
The life, therefore, resides in the blood (as
we are also informed in our sacred writings),3
because in it life and the soul first show them-
selves, and last become extinct. For I have fre-
quently found, from the dissection of living
animals, as I have said, that the heart of an ani-
mal that was dying, that was dead, and had
ceased to breathe, still continued to pulsate for
a time, and retained its vitality. The ventricles
failing and coming to a stand, the motion still
goes on in the auricles, and finally in the right
auricle alone; and even when all motion has
ceased, there the blood may still be seen affected
with a kind of undulation and obscure palpita-
tion or tremor, the last evidence of life. Every-
one, indeed, may perceive that the blood— this
author of pulsation and life— longest retains its
heat; for when this is gone, and it is no longer
blood, but gore, so is there, then, no hope of a
return to life. But, truly, as has been stated,
both in the chick in ovo and in the moribund
animal, if you but apply some gentle stimulus
either to the punctum saliens or to the right
auricle of the heart after the failure of all pulsa-
tion, forthwith you will see motion, pulsation,
and life restored to the blood— provided al-
ways, be it understood, that the innate heat
and vital spirit have not been wholly lost.
From this it clearly appears that the blood is
the generative part, the fountain of life, the
first to live, the last to die, and the primary seat
of the soul; the element in which, as in a foun-
tain head, the heat first and most abounds and
flourishes; from whose influxive heat all the
other parts of the body are cherished, and ob-
tain their life; for the heat, the companion of
the blood, flows through and cherishes and pre-
serves the whole body, as I formerly demon-
strated in my work on the motion of the blood.
And since blood is found in every particle of
the body, so that you can nowhere prick with a
needle, nor make the slightest scratch, but
blood will instantly appear, it seems as if, with-
out this fluid, the parts could neither have heat
nor life. So that the blood, being in ever so
trifling a degree concentrated and fixed — Hip-
pocrates called the state &7r6Xt;^ts r&v <£Xe/3coi',
stasis of the veins— as in lipothymia, alarm, ex-
posure to severe cold, and on the accession of a
febrile paroxysm, the whole body is observed to
become cold and torpid, and, overspread with
pallor and livor, to languish. But the blood, re-
called by stimulants, by exercise, by certain
2 Leviticus, 17. n, 14.
432
WILLIAM HARVEY
emotions of the mind, such as joy or anger, sud-
denly all is hot, and flushed, and vigorous, and
beautiful again.
Therefore it is that the red and sanguine
parts, such as the flesh, are alone spoken of as
hot, and the white and bloodless parts, on the
contrary, such as the tendons and ligaments,
are designated as cold. And as red-blooded ani-
mals excel exsanguine creatures, so also, in our
estimate of the parts, are those which are more
liberally furnished with native heat and blood,
held more excellent than all the others. The
liver, spleen, kidneys, lungs, and heart itself—-
parts which are especially entitled viscera— if
you will but squeeze out all the blood they con-
tain, become pale and fall within the category
of cold parts. The heart itself, I say, receives in-
fluxive heat and life along with the blood that
reaches it, through the coronary arteries; and
only so long as the blood has access to it. Neither
can the liver perform its office without the in-
fluence of the blood and heat it receives through
the coeliac artery; for there is no influx of heat
without an afflux of blood by the arteries, and
this is the reason wherefore, when parts are first
produced, and before they have taken upon
them the performance of their respective du-
ties, they all look bloodless and pale, in conse-
quence of which they were formerly regarded
as spermatic by physicians and anatomists, and
in generation it was usual to say that several
days were passed in the milk. The liver, lungs,
and substance of the heart itself, when they
first appear, are extremely white; and, indeed,
the cone of the heart and the walls of the ven-
tricles are still seen to be white, when the auri-
cles, replete with crimson blood, are red, and
the coronary vein is purple with its stream. In
like manner, the parenchyma of the liver is
white, when its veins and their branches are red
with blood; nor does it perform any duty until
it is penetrated with blood.
The blood, in a word, so flows around and
penetrates the whole body, and imparts heat
and life conjoined to all its parts, that the vital
principle, having its first and chief seat there,
may truly be held as resident in the blood; in
this way, in common parlance, it comes to be
all in all, and all in each particular part.
But so little is it true, as Aristotle and the
medical writers assert, that the liver and the
heart are the authors and compounders of the
blood, that the contrary even appears most
obviously from the formation of the chick in
ovoy viz., that the blood is much rather the
fashioner of the heart and liver; a fact which
physicians themselves appear unintentionally
to confirm, when they speak of the parenchyma
of the liver as a kind of effusion of blood, as if
it were nothing more than so much blood co-
agulated there. But the blood must exist before
it can either be shed or coagulated; and experi-
ence palpably demonstrates that the thing is so,
seeing that the blood is already present before
there is a vestige either of the body or of any
viscus; and that in circumstances where none
of the mother's blood can by possibility reach
the embryo, an event which is vulgarly held to
occur among viviparous animals.
The liver of fishes is always perceived of a
white colour, though their veins are of a deep
purple or black; and our fowls, the fatter they
become, the smaller and paler grows the liver.
Cachectic maidens, and those who labour under
chlorosis, are not only pale and blanched in
their bodies generally, but in their livers as
well, a manifest indication of a want of blood in
their system. The liver, therefore, receives both
its heat and colour from the blood; the blood is
in no wise derived from the liver.
From what has now been said, then, it ap-
pears that the blood is the first engendered
part, whence the living principle in the first
instance gleams forth, and from which the first
animated particle of the embryo is formed;
that it is the source and origin of all other parts,
both similar and dissimilar, which thence obtain
their vital heat and become subservient to it in
its duties. But the heart is contrived for the
sole purpose of ministering between the veins
and the arteries — of receiving blood from the
veins, and, by its ceaseless contractions, of pro-
pelling it to all parts of the body through the
arteries.
This fact is made particularly striking, when
we find that neither is there a heart found in
every animal, neither does it necessarily and in
every instance pulsate at all times where it is
encountered; the blood, however, or a fluid
which stands in lieu of it, is never wanting.
EXERCISE 52. Of the blood as prime element in the
body
It is unquestionable, then, and obvious to
sense, that the blood is the first formed, and
therefore the genital part of the embryo, and
that it has all the attributes which have been
ascribed to it in the preceding exercise. It is
both the author and preserver of the body; it
is the principal element moreover, and that in
which the vital principle (anima) has its dwell-
ing-place. Because, as already said, before there
ANIMAL GENERATION
433
is any particle of the body obvious to sight, the
blood is already extant, has already increased in
quantity, "and palpitates within the veins," as
Aristotle1 expresses it, "being moved hither and
thither, and being the only humour that is dis-
tributed to every part of the animal body. The
blood, moreover, is that alone which lives and is
possessed of heat whilst life continues.'*
And further, from its various motions in ac-
celeration or retardation, in turbulence and
strength, or debility, it is manifest that the
blood perceives things that tend to injure by
irritating, or to benefit by cherishing it. We
therefore conclude that the blood lives of itself,
and supplies its own nourishment; and that it
depends in nowise upon any other part of the
body, which is either prior to itself or of greater
excellence and worth. On the contrary, the
whole body, as posthumous to it, as added and
appended, as it were, to it, depends on the
blood, though this is not the place to prove the
fact; I shall only say, with Aristotle, that "The
nature of the blood is the undoubted cause
wherefore many things happen among animals,
both as regards their tempers and their capaci-
ties."2 To the blood, therefore, we may refer as
the cause not only of life in general — inasmuch
as there is no other inherent or influxive heat
that may be the immediate instrument of the
living principle except the blood— but also of
longer or shorter life, of sleep and watching, of
genius or aptitude, strength, &c. "For through
its tenuity and purity," says Aristotle in the
same place, "animals are made wiser and have
more noble senses; and in like manner they are
more timid and courageous, or passionate and
furious, as their blood is more dilute, or replete
with dense fibres."
Nor is the blood the author of life only, but,
according to its diversities, the cause of health
and disease likewise: so that poisons, which
come from without, such as poisoned wounds,
unless they infect the blood, occasion no mis-
chief. Life and death, therefore, flow for us
from the same spring. "If the blood becomes
too diffluent," says Aristotle,3 "we fall sick; for
it sometimes resolves itself into such a sanguino-
lent serum, that the body is covered with a
bloody sweat; and if there be too great a loss of
blood, life is gone." And, indeed, not only do
the parts of the body at all times become tor-
pid when blood is lost, but if the loss be exces-
sive, the animal necessarily dies. I do not think
1 History of Animals , HI. 19.
2 On the Pans of Animals, 11. 4.
1 History of Animals, in. 19.
it requisite to quote any particular experiment
in confirmation of these views: the whole sub-
ject would require to be treated specially.
The admirable circulation of the blood orig-
inally discovered by me, I have lived to see
admitted by almost all; nor has aught as yet
been urged against it by anyone which has
seemed greatly to require an answer. Where-
fore, I imagine that I shall perform a task not
less new and useful than agreeable to philoso-
phers and medical men, if I here briefly dis-
course of the causes and uses of the circulation,
and expose other obscure matters respecting
the blood; if I show, for instance, how much
it concerns our welfare that by a wholesome
and regulated diet we keep our blood pure and
sweet. When I have accomplished this it will no
longer, I trust, seem so improbable and absurd
to anyone as it did to Aristotle4 in former
times, that the blood should be viewed as the
familiar divinity, as the soul itself of the body,
which was the opinion of Critias and others,
who maintained that the prime faculty of the
living principle (anima) was to feel, and that
this faculty inhered in the body in virtue of the
nature of the blood. Thales, Diogenes, Heracli-
tus, Alcmaeon, and others, held the blood to be
the soul, because, by its nature, it had a faculty
of motion.
Now that both sense and motion are in the
blood is obvious from many indications, al-
though Aristotle6 denies the fact. And, indeed,
when we see him, yielding to the force of truth,
brought to admit that there is a vital principle
even in the hypenemic egg; and in the spermat-
ic fluid and blood a "certain divine something
corresponding with the element of the stars,"
and that it is vicarious of the Almighty Creator;
and if the moderns be correct in their views
when they say that the seminal fluid of animals
emitted in coitu is alive, wherefore should we
not, with like reason, affirm that there is a vital
principle in the blood, and that when this is
first ingested and nourished and moved, the
vital spark is first struck and enkindled ? Un-
questionably the blood is that in which the
vegetative and sensitive operations first pro-
claim themselves; that in which heat, the pri-
mary and immediate instrument of life, is in-
nate; that which is the common bond between
soul and body, and the vehicle by which life is
conveyed into every particle of the organized
being.
4 On the Soul, i. 2.
6 History of Animals, i. 19; On the Parts of Animals,
ii. 3-
434
WILLIAM HARVEY
Besides, if it be a matter of such difficulty to
understand the spermatic fluid as we have
found it, to fathom how through it the forma-
tion of the body is made to begin and proceed
with such foresight, art, and divine intelli-
gence, wherefore should we not, with equal
propriety, admit an exalted nature in the blood,
and think at least as highly of it as we have
been led to do of the semen? — the rather, as
this fluid is itself produced from the blood, as
appears from the history of the egg; and the
whole organized body not only derives its ori-
gin, as from a genital part, but even appears
to owe its preservation to the blood.
We have, indeed, already said so much inci-
dentally above, intending to speak on the sub-
ject more particularly at another time. Nor do
I think that we are here to dispute whether it is
strictly correct to speak of the blood as a fart;
some deny the propriety of such language,
moved especially by the consideration that it is
not sensible, and that it flows into all parts of
the body to supply them with nourishment.
For myself, however, I have discovered not a
few things connected with the manner of gen-
eration which differ essentially from those mo-
tions which philosophers and medical writers
generally either admit or reject. At this time I
say no more on this point; but though I admit
the blood to be without sensation, it does not
follow that it should not form a portion, and
even a very principal portion, of a body which
is endowed with sensibility. For neither does
the brain nor the spinal marrow, nor the crys-
talline or the vitreous humour of the eye, feel
anything, though, by the common consent of
all, philosophers and physicians alike, these are
parts of the body. Aristotle placed the blood
among the panes similares; Hippocrates, as the
animal body according to him is made up of
containing, contained, and impelling parts, of
course, reckoned the blood among the number
of parts contained.
But we shall have more to say on this topic
when we treat of that wherein a part consists,
and how many kinds of parts there are. Mean-
time, I cannot be silent on the remarkable fact
that the heart itself, this most distinguished
member in the body, appears to be insensible.
A young nobleman, eldest son of the Vis-
count Montgomery, when a child, had a severe
fall, attended with fracture of the ribs of the
left side. The consequence of this was a suppu-
rating abscess, which went on discharging
abundantly for a long time, from an immense
gap in his side; this I had from himself and
other credible persons who were witnesses. Be-
tween the eighteenth and nineteenth years of
his age, this young nobleman, having travelled
through France and Italy, came to London,
having at this time a very large open cavity in
his side, through which the lungs, as it was be-
lieved, could both be seen and touched. When
this circumstance was told as something mirac-
ulous to his Serene Majesty King Charles, he
straightway sent me to wait on the young man,
that I might ascertain the true state of the case.
And what did I find? A young man, well
grown, of good complexion, and apparently
possessed of an excellent constitution, so that I
thought the whole story must be a fable. Hav-
ing saluted him according to custom, however,
and informed him of the king's expressed de-
sire that I should wait upon him, he immedi-
ately showed me everything, and laid open his
left side for my inspection, by removing a plate
which he wore there by way of defence against
accidental blows and other external injuries. I
found a large open space in the chest, into
which I could readily introduce three of my
fingers and my thumb; which done, I straight-
way perceived a certain protuberant fleshy
part, affected with an alternating extrusive and
intrusive movement; this part I touched gen-
tly. Amazed with the novelty of such a state, I
examined everything again and again, and
when I had satisfied myself, I saw that it was a
case of old and extensive ulcer, beyond the
reach of art, but brought by a miracle to a kind
of cure, the interior being invested with a mem-
brane, and the edges protected with a tough
skin. But the fleshy part (which I at first sight
took for a mass of granulations, and others had
always regarded as a portion of the lung, from
its pulsating motions and the rhythm they ob-
served with the pulse)— when the fingers of one
of my hands were applied to it, those of the
other to the artery at the wrist — as well as from
their discordance with the respiratory move-
ments, I saw was no portion of the lung that I
was handling, but the apex of the heart! cov-
ered over with a layer of fungous flesh by way
of external defence, as commonly happens in
old foul ulcers. The servant of this young man
was in the habit daily of cleansing the cavity
from its accumulated sordes by means of injec-
tions of tepid water; after which the plate was
applied, and, with this in its place, the young
man felt adequate to any exercise or expedition,
and, in short, he led a pleasant life in perfect
safety.
Instead of a verbal answer, therefore, I car-
ANIMAL GENERATION
435
ried the young man himself to the king, that
his majesty might with his own eyes behold this
wonderful case: that, in a man alive and well,
he might, without detriment to the individual,
observe the movement of the heart, and, with
his proper hand even touch the ventricles as
they contracted. And his most excellent maj-
esty, as well as myself, acknowledged that the
heart was without the sense of touch; for the
youth never knew when we touched his heart,
except by the sight or the sensation he had
through the external integument.
We also particularly observed the move-
ments of the heart, viz. : that in the diastole it
was retracted and withdrawn; whilst in the sys-
tole it emerged and protruded; and the systole
of the heart took place at the moment the dias-
tole or pulse in the wrist was perceived ; to con-
clude, the heart struck the walls of the chest,
and became prominent at the time it bounded
upwards and underwent contraction on itself.
Neither is this the place for taking up that
other controversy; to wit, whether the blood
alone serves for the nutrition of the body ? Aris-
totle in several places contends that the blood
is the ultimate aliment of the body, and in this
view he is supported by the whole body of
physicians. But many things of difficult inter-
pretation, and that hang but indifferently to-
gether, follow from this opinion of theirs. For
when the medical writers speak of the blood in
their physiological disquisitions, and teach that
the above is its sole use and end, viz. : to supply
nourishment to the body, they proceed to com-
pose it of four humours, or juices, adducing
arguments for such a view from the combina-
tions of the four primary qualities; and then
they assert that the mass of the blood is made
up of the two kinds of bile, the yellow and the
black, of pituita, and the blood properly so
called. And thus they arrive at their four hu-
mours, of which the pituita is held to be cold and
moist; the black bile cold and dry; the yellow
bile hot and dry; and the blood hot and moist.
Further, of each of these several kinds, they
maintain that some are nutritious, and com-
pose the whole of the body; others, again, they
say are excrementitious. Still further, they sup-
pose that the blood proper is composed of the
nutritious or heterogeneous portions; but the
constitution of the mass is such that the pituita
is a cruder matter, which the more powerful
native heat can convert into perfect blood.
They deny, however, that the bile can by any
means be thus transformed into blood; al-
though the blood, they say, is readily changed
into bile, an event which they conceive takes
place in melancholic diseases, through an ex-
cess of the concocting heat.
Now, if all this were true, and there be no
retrogressive movement, viz., from black bile
to bile, from bile to blood, they would be
brought to the dilemma of having to admit
that all the juices were present for the produc-
tion of black bile, and that this was a principal
and most highly concocted nutriment. It would
further be imperative on them to recognize a
kind of twofold blood, *>/£., one consisting of
the entire mass of fluid contained in the veins,
and composed of the four humours aforesaid;
and another consisting of the purer, more fluid
and spirituous portion, the fluid, which in the
stricter sense they call blood, which some of
them contend is contained in the arteries apart
from the rest, and which they then depute
upon sundry special offices. On their own show-
ing, therefore, the pure blood is no aliment for
the body, but a certain mixed fluid, or rather
black bile, to which the rest of the humours
tend.
Aristotle,1 too, although he thought that the
blood existed as a means of nourishing the
body, still believed that it was composed, as it
were, of several portions, viz.> of a thicker and
black portion which subsides to the bottom of
the basin when the blood coagulates, and this
portion he held to be of an inferior nature; "for
the blood," he says, "if it be entire, is of a red
colour and sweet taste; but if vitiated either by
nature or disease, it is blacker."2 He also will
have it fibrous in part or partly composed of
fibres, which being removed, he continues,3
the blood neither sets nor becomes any thicker.
He further admitted a sanies in the blood:
"Sanies is unconcocted blood, or blood not yet
completely concocted, or which is as yet dilute
like serum." And this part, he says, is of a colder
nature. The fibrous he believed to be the
earthy portion of the blood.
According to the view of the Stagirite, there-
fore, the blood of different animals differs in
several ways; in one it is more serous and thin-
ner, a kind of ichor or sanies, as in insects, and
the colder and less perfect animals; in another
it is thicker, more fibrous, and earthy, as in the
wild boar, bull, ass, &c. In some where the con-
stitution is distempered, the blood is of a blacker
hue; in others it is bright, pure, and florid, as in
birds, and the human subject especially.
1 On the Parts of Animals •, n. 3.
2 History ofAmmals, in. 19.
436
WILLIAM HARVEY
Whence, it appears, that in the opinion of the
physicians, as well as of Aristotle, the blood
consists of several parts, in some sort of the
same description, according to the views of
each. Medical men, indeed, only pay attention
to human blood, taken in phlebotomy and con-
tained in cups and coagulated. But Aristotle took
a view of the blood of animals generally, or of
the fluid which is analogous to it. And I, omit-
ting all points of controversy, and passing by
any discussion of the inconveniences that wait
upon the opinions of writers in general, shall
here touch lightly upon the points that all are
agreed in, that can be apprehended by the senses,
and that pertain more especially to our sub-
ject; intending, however, to treat of everything
at length elsewhere.
Although the blood be, as I have said, a por-
tion of the body — the primogenial and princi-
pal part, indeed — still, if it be considered in its
mass, and as it presents itself in the veins, there
is nothing to hinder us from believing that it
contains and concocts nourishment within it-
self, which it applies to all the other parts of
the body. With the matter so considered, we
can understand how it should both nourish and
be nourished, and how it should be both the
matter and the efficient cause of the body, and
have the natural constitution which Aristotle
held necessary in a primogenial part, viz., that
it should be partly of similar, partly of dissimi-
lar constitution; for he says, "As it was requi-
site for the sake of sensation that there should
be similar members in animal bodies, and as the
faculty of perceiving, the faculty of moving,
and the faculty of nourishing, are all contained
in the same member (viz., the primogenate
particle), it follows necessarily that this mem-
ber, which originally contains inherent princi-
ples of the above kind, be extant both simply,
that it may be capable of sensation of every
description, and dissimilarly, that it may move
and act. Wherefore, in the tribes that have
blood, the heart is held to be such a member;
in the bloodless tribes, however, it is propor-
tional to their state.*'
Now, if Aristotle understands by the heart
that which first appears in the embryo of the
chick in ovo, the blood, to wit, with its contain-
ing parts— the pulsating vesicles and veins, as
one and the same organ, I conceive that he has
expressed himself most accurately; for the
blood, as it is seen in the egg and the vesicles, is
partly similar and partly dissimilar. But if he
understands the matter otherwise, what is seen
in the egg sufficiently refutes him, inasmuch as
the substance of the heart, considered inde-
pendently of the blood — the ventricular cone
— is engendered long afterwards, and continues
white without any infusion of blood, until the
heart has been fashioned into that form of
organ by which the blood is distributed through
the whole body. Nor indeed does the heart
even then present itself with the structure of a
similar and simple part, such as might become a
primogenial part, but is seen to be fibrous,
fleshy, or muscular, and indeed is obviously
what Hippocrates styled it, a muscle or instru-
ment of motion. But the blood, as it is first per-
ceived, and as it pulsates, included within its
vesicle, has as manifestly the constitution which
Aristotle held necessary in a principal part. For
the blood, whilst it is naturally in the body, has
everywhere apparently the same constitution;
when extravasated, however, and deprived of
its native heat, immediately, like any dissimi-
lar compound it separates into several parts.
Were the blood destined by nature, how-
ever, for the nourishment of the body only, it
would have a more similar constitution, like the
chyle or the albumen of the egg; or at all events
it would be truly one and a single body com-
posed of the parts or juices indicated, like the
other humours, such as bile of either kind, and
pituita or phlegm, which retain the same form
and character without the body, which they
showed within their appropriate receptacles;
they undergo no such sudden change as the
blood.
Wherefore, the qualities which Aristotle
ascribed to a principal part are found associated
in the blood; which as a natural body, existing
heterogeneously or dissimilarly, is composed of
these juices or parts; but as it lives and is a very
principal animal part, consisting of these juices
mingled together, it is an animated similar part,
composed of a body and a vital principle. When
this living principle of the blood escapes, how-
ever, in consequence of the extinction of the
native heat, the primary substance is forthwith
corrupted and resolved into the parts of which
it was formerly composed; first into cruor,
afterwards with red and white parts, those of
the red parts that are uppermost being more
florid, those that are lowest being black. Of
these parts, moreover, some are fibrous and
tough (and these are the uniting medium of the
rest), others ichorous and serous, in which the
mass of coagulum is wont to swim. Into such a
serum does the blood almost wholly resolve it-
self at last. But these parts have no existence
severally in living blood ; it is in that only which
ANIMAL GENERATION
437
has become corrupted and is resolved by death
that they are encountered.
Besides the constituents of the blood now
indicated, there is yet another which is seen in
the blood of the hotter and stronger animals,
such as horses, oxen, and men also of ardent
constitution. This is seen in blood drawn from
the body as it coagulates, in the upper part of
the red mass, and bears a perfect resemblance
to hartshorn- jelly, or mucilage, or thick white
of egg. The vulgar believe this matter to be the
pituita; Aristotle designated it the crude and
unconcocted portion of the blood.
I have observed that this part of the blood
differs both from the others and from the more
serous portion in which the coagulated clot is
wont to swim in the basin, and also from the
urine which percolates through the kidneys
from the blood. Neither is it to be regarded as
any more crude or colder portion of the blood,
but rather, as I conceive, as a more spiritual
part; a conclusion to which I am moved by two
motives: first, because it swims above the
bright and florid portion— commonly thought
to be the arterial blood — as if it were hotter
and more highly charged with spirits, and takes
possession of the highest place in the disinte-
gration of the blood.
Secondly, in venesection, blood of this kind,
which is mostly met with among men of warm
temperament, strong and muscular, escapes in
a longer stream and with greater force, as if
pushed from a syringe, in the same way as we
say that the spermatic fluid which is ejected
vigorously and to a distance is both more fruit-
ful and full of spirits.
That this mucaginous matter differs greatly
from the ichorous or watery part of the blood,
which, as if colder than the rest, subsides to the
bottom of the basin, appears on two distinct
grounds: for the watery and sanious portion is
too crude and unconcocted ever to pass into
purer and more perfect blood; and the thicker
and more fibrous mucus swimming above the
clot of the blood itself appears more concoct
and better elaborated than this; and so in the
resolution or separation of the blood it comes
that the mucus occupies the upper place, the
sanies the lower; the clot and red parts, how-
ever—both those of a brighter and those of a
darker colour — occupy the middle space.
For it is certain that not only this part, but
the whole blood, and indeed the flesh itself— as
may be seen in criminals hung in chains— may
be reduced to an ichorous sanies; that is to say,
become resolved into the matters of which they
were composed, like salt into the lixivium from
which it had been obtained. In like manner,
the blood taken away in any cachexy abounds
in serum, and this to such an extent that oc-
casionally scarce any clot is seen — the whole
mass of blood forms one sanies. This is observed
in leucophlegmatia, and is natural in bloodless
animals.
Further, if you take away some blood short-
ly after a meal, before the second digestion has
been completed and the serum has had time to
descend by the kidneys, or at the commence-
ment of an attack of intermittent fever, you
will find it sanious, inconcoct, and abounding
in serum. On the contrary, if you open a vein
after fasting, or a copious discharge of urine or
sweat, you will find the blood thick, as if with-
out serum, and almost wholly condensed into
clot.
And in the same way as in coagulating blood
you find a little of the afore-mentioned super-
natant mucus, so if you expose the sanies in
question, separated from the clot, to a gentle
heat over the fire, you will find it to be speedily
changed into the mucus; an obvious indication
that the water or sanies which separates from
the blood in the basin, is perchance a certain
element in the urine, but not the urine itself,
although in colour and consistence it seems so
in fact. The urine is not coagulated or con-
densed into a fibrous mucus, but rather into a
lixivium; the watery or sanious portion of the
urine, however, when lightly boiled, does oc-
casionally run into a mucus that swims through
the fluid; in the same way, as the mucus in
question rendered recrudescent by corruption,
liquefies and returns to the state of sanies.
So far at this time have I thought fit to pro-
duce these my own observations on this constit-
uent of the blood, intending to speak more
fully of it as well as of the other constituents
cognizable by the senses, and admitted by Aris-
totle and the medical writers.
That I may not seem to wander too widely
from my purpose, I would here have it under-
stood that with Aristotle I receive the blood as
a part of the living animal body, and not as it is
commonly regarded in the light of mere gore.
The Stagirite says: "The blood is warm, in the
sense in which we should understand warm
water, did we designate that fluid by a simple
name, not viewing it as heated. For heat be-
longs to its nature; just as whiteness is in the
nature of a white man. But when the blood be-
comes hot through any affection or passion, it
is not then hot of itself. The same thing must
438
WILLJAM HARVEY
be said in regard to the qualities of dryness and
moistness. Wherefore, in the nature of such
things they are partly hot and partly moist;
but separated, they congeal and become cold;
and such is the blood."1
The blood, consequently, as it is a living ele-
ment of the body, is of a doubtful nature, and
falls to be considered under two points of view.
Materially and per se it is called nourishment;
but formally and in so far as it is endowed with
heat and spirits, the immediate instruments of
the vital principle, and even with vitality (am-
mo), it is to be regarded as the familiar divinity
and preserver of the body, as the generative
first engendered and very principal part. And
as the prolific egg contains within it the matter,
instrument, and framer of the future pullet,
and all physicians admit a mixture of the semi-
nal fluids of the two sexes in the uterus during
or immediately after intercourse as constituting
the mixed cause, both material and efficient, of
the foetus; so might one with more propriety
maintain that the blood was both the matter
and preserver of the body, though not the sole
aliment; because it is observed that in animals
which die of hunger, and in men who perish of
marasmus, a considerable quantity of blood is
still found after death in the veins. And fur-
ther, in youthful subjects still growing, and in
aged individuals declining and falling away, the
relative quantity of blood continues the same,
and is in the ratio of the flesh that is present, as
if the blood were a part of the body, but not
destined solely for its nourishment; for if it
were so, no one would die of hunger so long as
he had any blood left in his veins, just as the
lamp is not extinguished whilst there is a drop
of inflammable oil left in the cruse.
Now when I maintain that the living princi-
ple resides primarily and principally in the
blood, I would not have it inferred from thence
that I hold all bloodletting in discredit, as dan-
gerous and injurious; or that I believe with the
vulgar that in the same measure as blood is lost,
is life abridged, because the sacred writings tell
us that the life is in the blood; for daily expe-
rience satisfies us that bloodletting has a most
salutary effect in many diseases, and is indeed
the foremost among all the general remedial
means: vitiated states and plethora of the
blood, are causes of a whole host of diseases; and
the timely evacuation of a certain quantity of
the fluid frequently delivers patients from
very dangerous diseases, and even from immi-
nent death. In the same measure as blood is de-
1 On the Parts of Animals, u. 3.
tracted, therefore, under certain circumstances,
it may be said that life and health are added.
This indeed nature teaches, and physicians
at all events propose to themselves to imitate
nature; for copious critical discharges of blood
from the nostrils, from hemorrhoids, and in the
shape of the menstrual flux, often deliver us
from very serious diseases. Young persons,
therefore, who live fully and lead indolent lives,
unless between their eighteenth and twentieth
years they have a spontaneous hemorrhage
from the nose or lower parts of the body, or
have a vein opened, by which they are relieved
of the load of blood that oppresses them, are
apt to be seized with fever or smallpox, or they
suffer from headache and other morbid symp-
toms of various degrees of severity and danger.
Veterinary surgeons are in the habit of begin-
ning the treatment of almost all the diseases of
cattle with bloodletting.
EXERCISE 53. Of the inferences deducible from the
course of the umbilical vessels in the egg
We find the blood formed in the egg and em-
bryo before any other part; and almost at the
same moment appear its receptacles, the veins
and the vesicula pulsans. Wherefore, if we re-
gard the punctum saliens as the heart, and this
along with the blood and the veins as constitut-
ing one and the same organ, conspicuous in the
very commencement of the embryo, although
we should admit that the proper substance of
the heart was deposited subsequently, still we
should be ready to admit with Aristotle that
the heart (an organ made up of ventricles, auri-
cles, vessels, and blood) was in truth the princi-
pal and primogenate part of the body, its own
prime and essential element having been the
blood, both in the order of nature and of genet-
ic production.
The parts that in generation succeed the
blood are the veins, for the blood is necessarily
inclosed and contained in vessels; so that, as
Aristotle observes, we find two meatus venales
even from the very first, which canals, as we
have shown in our history, afterwards consti-
tute the umbilical vessels. It seems necessary,
therefore, to say something here of the situa-
tion and course of these vessels.
In the first place, then, it is to be observed
that all the arteries and veins have their origin
from the heart and are, as it were, appendices
or parts added to the central organ. If, there-
fore, you carefully examine the embryo of the
human subject, or one of the lower animals, and
having divided the vena cava between the right
ANIMAL GENERATION
439
auricle and the diaphragm, look into it upwards
or towards the heart, you will perceive three
foramina, the largest and most posterior of
which tending to the spine is the vena cava; the
anterior and lesser proceeds to the root and
trunk of the umbilical vessels; the third and
least of all enters the liver and is the origin and
trunk of all the ramifications distributed to the
convexity of that organ. Whence it clearly ap-
pears that the veins do by no means all proceed
from the liver as their origin and commence-
ment, but from the heart — unless indeed any
one would be hardy enough to contend that a
vessel proceeded from its branches, not the
branches from the trunk of the vessel.
Moreover, as the vessels in question are dis-
tributed equally to the albumen and vitellus of
the egg, not otherwise than as the roots of trees
are connected with the ground, it is obvious
that both of these substances must serve for the
nutriment of the embryo, and that they are
taken up and carried to it by these vessels.
But this view is opposed to that of Aristotle,
who everywhere maintains that the chick is
formed from the albumen, and receives nourish-
ment through the umbilicus alone. The al-
bumen indeed is first consumed, and the yelk
serves subsequently for food, supplying the
place of the milk, which viviparous animals re-
ceive after their birth from their mothers. The
food which Nature provides for the young of
viviparous tribes in the dug of the mother, she
supplies in the yelk of the egg to the young of
oviparous animals. Whence it happens, that
when the albumen is almost wholly consumed,
the vitellus still remains nearly entire in the
egg, the chick being already perfect and com-
plete; more than this, the yelk is still found in
the abdomen of the chick long after its exclu-
sion. Aristotle discovered some on the eight-
eenth day after the hatching; and I have my-
self seen a small quantity connected with the
intestine at the end of six weeks from that
epoch.
Nevertheless, from the yelk (which certainly
does not decrease in the same ratio as the albu-
men whilst the chick is forming) that is taken
into the abdomen of the chick, and from the
distribution of vessels through its substance,
the whole of these collecting into a single
trunk which enters the porta of the liver, and
doubtless carrying that portion of yelk they
have absorbed for more perfect elaboration in
that viscus — these and other arguments of the
like kind force me to say that I cannot do other-
wise than admit with Aristotle that the yelk
supplies food to the chick, and is analogous to
milk.
The whole of the yelk, indeed, does not re-
main after the foetus of the fowl is fully formed ;
for a certain portion of it has been liquefied on
the very first appearance of the embryo, and re-
ceives branches of vessels no less than the albu-
men, by which, already prepared, it is carried
as nourishment for the chick; still it is certain
that the greater portion of the yelk remains
after the disappearance of the albumen; that it
is laid up in the abdomen of the chick when
excluded, and, attracted or absorbed by the
branches of the vena portae, that it is finally
carried to the liver.
It is manifest, therefore, that the chick when
hatched, is nourished by the yelk in the first
period of its independent existence. And as
within the egg the embryo was nourished part-
ly by the albumen, partly by the vitellus, but
principally by the albumen, which is both
present in larger quantity, and is more speedily
consumed, so when the chick is hatched, and
when all the nourishment that is taken must
pass through the liver to undergo ulterior prep-
aration, is it nourished partly by the vitellus
and partly by chyle absorbed from the intes-
tines, but principally by chyle, which the host
of subdivisions of the mesenteric vessels seize
upon, whilst there is but a single vessel from the
porta distributed to the vitellus, and by and by
but little of it remains. Nature, therefore, acts
as does the nurse, who gradually habituates her
infant to the food which is to take the place of
her failing supply of milk. The pullet is thus
gradually brought from food of more easy to
food of more difficult digestion, from yelk to
chyle.
Wherefore, there is every reason for what we
perceive in connexion with the course of the
veins in the egg. When the embryo first begins
to be formed, they are distributed to the colli-
quament only, where the blood finds suitable
nutriment and matter for the formation of the
body; but by and by they extend into the thin-
ner albumen, whence the chick, whilst it is yet
in the state of gelatine or mucor, and resembles
a maggot in form, derives its increase; the
branches next extend into the thicker albumen,
and then into the vitellus, that they may also
contribute to the support of the foetus, which,
having at length arrived at maturity and been
extruded, still preserves a portion of the yelk
(or milk) within its abdomen, whereby it is
maintained in part, in part by food selected
and prepared for it by the mother, until it is
440
WILLIAM HARVEY
able to look out for and to digest its own ali-
ment. Thus does nature most wisely provide
food through the whole round of generation,
suited to the various strength of the digestive
faculty in the future being. In the first period
of the fatal chick's existence a more delicate
food is prepared for it; more advanced, firmer
and firmer food is supplied; and this is the rea-
son, I apprehend, wherefore, the perfect egg
consists not only of two portions of different
colours, but is even provided with two kinds of
albumen.
Now all this that we discover from actual ex-
perience of the matter accords with the opin-
ion of Aristotle, where he says: "The part
which is hot is best adapted to give form to the
limbs; that which is more earthy rather con-
duces to the constitution of the body and is
more remote. Wherefore in eggs of two colours,
the animal begins to be engendered from the
white (for the beginning of animal life is in the
hot), and derives its nourishment from the yel-
low. In the warmer animals, consequently,
these parts are kept distinct from one another,
viz.t that from which the beginning is derived,
and that whence the nourishment is obtained,
and the one is white, the other yellow."1
From what has now been said it appears that
the chick — and we shall show that it is not
otherwise in all other animals — arises and is
constituted, as it were, by a principle or soul
inherent in the egg, and that in the same way
the proper aliment is sought for and is supplied
within the egg; whereby it comes that the chick
is not dependent on its mother in the same way
as plants are dependent on the ground; and it is
not more correct to say that the chick is nour-
ished by the blood of its mother, or that its
heart beats, and that it lives through the
spirits of its parent, than it would be to assert
that it moved and felt through the organs, or
grew and attained to adult age through the
vital principle of its parent. It is manifest, on
the contrary, and is allowed by all that the
fetal chick is nourished through its umbilical
vessels; and that the vascular ramifications dis-
persed over the albumen and yelk imbibe nour-
ishment from them and convey it to the foetus.
It is also admitted that the chick, when ex-
cluded from the shell, is supplied with nourish-
ment, partly from yelk, partly from chyle, and
that in either case the aliment passes by the
same route, wi., by the vena portae into the
liver, the branches of this vessel effecting the
transit.
1 On the Generation of Animals y in. i.
It is therefore obvious, as I now say by the
way, that the chyle by which all animals are
nourished is brought by the mesenteric veins
from the intestines; nor is there occasion to
look for any new passage— by the lacteal ves-
sels, to wit— or any route in adult animals other
than that which we discover in the egg and
chick. But we shall recur more fully in another
place to the inconveniences of such an opinion
as that referred to.
Lastly, from the structure of the umbilical
vessels of the chick in ovo, some of which as
stated in the history are veins, others arteries,
it is legitimate to conclude that there is here a
circular motion of the blood, such as we have
already demonstrated in the animal body, in
our book On the Motion of the Bloody and this
for the sake of the nutrition and growth of the
embryo, and because the umbilical veins are
distributed to either fluid of the egg, that they
may thence bring nutriment to the chick, and
the arteries accompany the veins, that by their
affluxive heat the alimentary matter may be
duly concocted, liquefied, and made fit to an-
swer the ends of nutrition.
And hence it happens that wherever veins —
and here I would have it understood that both
arteries and veins are intended — make their
way into the albumen or vitellus, there these
fluids look liquefied and different from the rest.
For as soon as the branches of the veins shoot
forth, the upper portion of the albumen in
which they are implanted, passing into colli-
quament, becomes transparent, whilst the lower
portion, continuing thick and compact, is
pushed into the inferior angle of the egg. In like
manner a separation of the vitellus, as it seems
into two portions, makes its appearance, the
one being superior, and the other inferior, and
these do not differ less from one another in
character than melted differs from solid wax;
now this division corresponds to the two parts
which severally receive or do not receive blood-
vessels.
Hence are we further made more certain as
to the commencement of animal generation
and the prime inherent principle of the egg.
For it is assuredly known that the cicatricula or
spot on the yelk is the chief point in the egg,
that to which all the rest are subordinate, and
to which, if to any one thing more than an-
other, is to be referred the cause, whatever it
be, of fecundity in the egg:— certain it is that
the generation of the embryo is begun within
its precincts. Wherefore, as we have said, the
first effect of incubation is to cause dilatation of
ANIMAL GENERATION
441
the cicatricula, and the formation of the colli-
quament, in which the blood first flushes and
veins are distributed, and where the effects of
the native heat and the influence of the plastic
power first show themselves. And then, the
more widely the ramifications of these veins
extend, in the same proportion do indications
of the presence of the vital power and vegeta-
tive force appear. For every effect is a clear evi-
dence of its efficient cause.
In a word I say — from the cicatricula (in
which the first trace of the native heat ap-
pears) proceeds the entire process of genera-
tion; from the heart the whole chick, and from
the umbilical vessels the whole of the mem-
branes called secundines that surround it. We
therefore conclude that the parts of the embryo
are severally subordinate, and that life is first
derived from the heart.
EXERCISE 54. Of the order of the parts in generation
from an egg, according to Fabricius
Having already determined what part is to
be esteemed the first, the blood, to wit, with
its receptacles, the heart, veins, and arteries,
the next thing we have to do is to speak of the
rest of the parts of the body and of the order
and manner of their generation.
Fabricius, in whose footsteps we have re-
solved to tread, in speaking of the generation
of the chick in ovo, passes in review the actions
which take place in the egg, and by the effect
of which the parts are produced, discussing
them seriatim, as if a clearer view were thence
to be obtained of the order or sequence of gen-
eration. "There are three primary actions," he
says,1 "which present themselves in the egg of
the bird: ist, the generation of the embryo;
2d, its growth; 3d, its nourishment. The first,
or generation, is the proper action of the egg;
the second and third, viz., growth and nutri-
tion, go on for the major part without the egg,
though they are begun and also perfectly per-
formed within it. Now these actions, as they
flow from three faculties, the generative, the
nutritive, and auctive, so do three operations
follow them. From generation all the parts of
the chick result; from increase and nutrition,
the growth and maintenance of its body. From
studying the formation of the chick, we per-
ceive that, under the influence of the genera-
tive faculty, the parts of the creature which
formerly had no existence are produced: the
matter of the egg is changed into the organized
body of a chicken. But whilst any part or sub-
1 Op. supra cit., p. 41.
stance undergoes transmutation into another, it
must needs be that its proper essence under-
goes change, otherwise would it still remain as
it was and unaltered; it must at the same time
receive figure, position, and dimensions apt
and convenient to its new nature; and indeed
it is into these two states or circumstances that
procreation of matter resolves itself, viz., trans-
formation and conformation. The transforma-
tive and the formative faculties would, there-
fore, be the cause of these functions; and whilst
one of them has produced every individual
part of the chick, such as we see it, from the
chalaza of the egg, the other has given it figure,
articulations, and position, fitting it for its des-
tined uses. The first, the transformative or al-
terative faculty, is entirely natural, and acts
without all consciousness; and taking the hot,
the cold, the moist, and the dry, it alters all
through the substance of the chalaza, and in
altering this substance changes it into the com-
ponent parts of the chick, that is to say, into
flesh, bones, cartilages, ligaments, veins, arter-
ies, nerves, and all the other similar and simple
parts of the animal, and these, through the
proper and innate heat and spirit of the semen
of the cock, out of the substance of the egg,
that is to say, its chalaza; by altering and com-
muting, it engenders, creates, produces the
proper substance of the chick, imparting at the
same time to every substance its appropriate
quality. The other, which is called the forma-
tive faculty, and which out of similar forms dis-
similar parts— namely, giving them elegance
through figure, due dimensions, proper posi-
tion, and congruous number— -is much more
noble than the former, is possessed of consum-
mate sapience, and acts not naturally, but with
election, and consciousness, and intelligence.
For the formative faculty appears to have
exact cognizance and foresight both of the
future action and use of every part and organ.
So much of the primary action of the egg,
which is the generation of the chick, and to
accomplish which both the semen of the cock as
agent and fecundator, and the chalaza as mat-
ter are required. In the second place comes ac-
cretion or growth, which is accomplished by
nutrition, whose faculties consist in attraction,
retention, concoction, expulsion, and, finally,
apposition, agglutination, and assimilation of
food."
But for my part I neither regard such a dis-
tribution of actions as correct, or useful, or con-
venient in this place. It is incorrect, because
those actions which he would make distinct in
442
WILLIAM HARVEY
kind and in time — for instance, that parts are
first produced similar by the alterative or
transformative faculty, to be afterwards fash-
ioned and organized by the formative faculty,
and finally made to grow by the auctive facul-
ty— are never apparent in the generation of
the chick; for the several parts are produced
and distinguished and increased simultaneous-
ly. For although in the generation of those ani-
mals which are formed by metamorphosis,
where from matter previously existing, and al-
ready adequate in quantity and duly prepared,
ill the parts are made distinct and conformed
by transformation, as when a butterfly is formed
from a caterpillar, a silkworm from a grub, still
in generation by epigenesis the thing is very
different, nor do the same processes go on as in
ordinary nutrition, which is effected by the
various actions of different parts working to-
gether to a common end, the food being here
irst assumed and retained, then digested, next
distributed, and finally agglutinated. Nor is the
similar constitution the result of the transforma-
tive faculty, void of all foresight, as Fabricius
magined; but the organic comes from the
formative faculty which proceeds with both
:onsciousness and foresight. For generation and
growth do not proceed without nutrition, nor
lutrition or increase without generation; "to
lourish" being, in other terms, to substitute
or a certain quantity of matter lost as much
natter of the same quality, flesh or nerve, in
ieu of the matter, flesh or nerve, that has be-
:ome effete. But what is this but to make or
engender flesh or nerve? In like manner,
growth cannot go on without generation, for
ill natural bodies are increased by the accession
)f new particles similar to those of which they
brmerly consisted, and this, taking place ac-
:ording to all their dimensions, they are dis-
inguished as regards their parts, and are or-
ganized at the same time that they grow.
But to engender the chick is in truth nothing
:lse than to fashion or make its several mem-
>ers and organs, which, although they are pro-
luced in a certain order, and some are post-
;enate toothers— the less important to the more
mncipal organs—still, whilst the organs them-
elves are all distinguished, they are not en-
gendered in such wise and order that the simi-
ar parts are first formed, and the organic parts
ifterwards compounded from them; or so that
:ertain composing parts existed before other
impounded parts which must be fashioned
rom them. For although the head of the chick
nd the rest of the body exist in the shape of a
mucus or soft jelly, whence each of the parts is
afterwards formed in sequence, and all are of
similar constitution in the first instance, still
are they simultaneously produced and aug-
mented in virtue of the same processes directed
by the same agent; and in the same proportion
as the matter resembling jelly increases, in like
measure are the parts distinguished; for they
are engendered, transmuted, and formed simul-
taneously; similar and dissimilar parts exist to-
gether, and from a small similar organ a larger
one is produced. The thing, in short, is not
otherwise than it is among vegetables, where
from the straw proceeds the ear, the awns, and
the grain — distinctly, severally, and yet to-
gether; or as trees put forth buds, from which
are produced leaves, flowers, fruit, and finally
seed.
All this we learn from an attentive study of
the parts and processes of the incubated egg,
inasmuch as from things done, actions or oper-
ations are apprehended; from operations, facul-
ties or forces, and from these we then infer the
artificer, generator, or cause. In the generation
of the pullet, consequently, the actions or fac-
ulties of the engendering cause enumerated by
Fabricius, namely, the metamorphic and form-
ative, do not differ in kind, or even in the
relation of sequence, as that one is first and the
other second, but, as Aristotle is wont to say,
are one and the same in reason; not as happens
with reference to the actions of the nutritive
faculty — attraction, concoction, distribution
and apposition, to wit — which all come into
play in several places at several times. Were
this not so, the engendering cause itself would
be forced to make use of various instruments in
order to accomplish its various operations.
Fabricius, therefore, asserts erroneously that
the transmutative force works with the prop-
erties of the elements — hot, cold, moist, and
dry — as its instruments; whilst the formative
faculty acts independently of these and by a
more divine power, performing its task with
consciousness, as it seems, with foresight and
election. But if he had looked more closely at
the matter he would have seen that the forma-
tive as well as the metamorphic force made use
of the hot and the cold, the moist and the dry,
as instruments; nor would he have been less
struck with indications of the Supreme Artifi-
cer's interference in the processes of nutrition
and transformation than in that of formation
itself. For nature ordained each and all of these
faculties to some definite end, and everywhere
labours with forethought and intelligence.
ANIMAL GENERATION
443
Whatever it is in the seeds of plants which ren-
ders them fertile and exercises a plastic force in
their interior; whatever it is which in the egg
performs the duty of a most skilful artificer,
producing and fashioning the parts of the pul-
let, warming, cooling, moistening, drying, con-
cocting, condensing, hardening, softening and
liquefying at once, impressing distinctive char-
acters on each of them by means of configura-
tion, situation, constitution, temperament,
number and order— still is this something at
work, disposing and ordering all with no less of
foresight, intelligence, and choice in the busi-
ness of transmuting, than in the processes of
nutrition, growth, and formation.
The concoct ive and metamorphic, the nu-
tritive and augmentive faculties, which Fa-
bricius would have it act through the qualities
of hot, cold, moist, and dry, without all con-
sciousness, I maintain, on the contrary, work
no less to a definite end, and with not less of
artifice than the formative faculty, which Fa-
bricius declares has knowledge and foresight of
the future action and use of every particular
part and organ. In the same way as the arts of
the physician, cook, and baker, in which heat
and cold, moisture and dryness, and similar
natural properties are employed, require the
use of reason no less than the mechanical arts in
which either the hands or various instruments
are employed, as in the business of the black-
smith, statuary, potter, &c.; in the same way,
as in the greater world, we are told that "All
things are full of Jove," — Jovis omnia plena — so
in the slender body of the pullet, and in every
one of its actions, does the finger of God or na-
ture no less obviously appear.
Wherefore, if from manifestations it be legit-
imate to judge of faculties, we might say that
the vegetative acts appear rather to be per-
formed with art, election, and foresight, than
the acts of the rational soul and mind; and this
even in the most perfect man, whose highest
excellence in science and art, if we may take
the God for our guide, is that he KNOW HIM-
SELF.
A superior and more divine agent than man,
therefore, appears to engender and preserve
mankind, a higher power than the male bird to
produce a young one from the egg. We ac-
knowledge God, the supreme and omnipotent
creator, to be present in the production of all
animals, and to point, as it were, with a finger
to his existence in his works, the parents being
in every case but as instruments in his hands.
In the generation of the pullet from the egg all
things are indeed contrived and ordered with
singular providence, divine wisdom, and most
admirable and incomprehensible skill. And to
none can these attributes be referred save to
the Almighty, first cause of all things, by what-
ever name this has been designated, — the Di-
vine Mind by Aristotle; the Soul of the Universe
by Plato; the Natura Naturans by others; Sat-
urn and Jove by the ancient Greeks and Ro-
mans; by ourselves, and as is seeming in these
days, the Creator and Father of all that is in
heaven and earth, on whom animals depend
for their being, and at whose will and pleasure
all things are and were engendered.
Moreover, as I have said, I neither hold this
arrangement of the faculties of the vital princi-
ple, which Fabricius has placed at the head of
his account of the organs of generation, as cor-
rect in itself, nor as useful or calculated to as-
sist us in the matter we have in hand. For we
do not attain to a knowledge of effects from a
discussion of actions or faculties; the contrary is
rather the case: from actions we ascend to a
knowledge of faculties, inasmuch as manifesta-
tions are more cognizable to us than the powers
whence they proceed, and the parts which we
investigate already formed are more readily ap-
preciated than the actions whence they pro-
ceed.
Neither is it well from the generation of a
single chick from an egg, to venture upon gen-
eral conclusions, which can in fact only be cor-
rectly arrived at after extensive observations
on the mode of generation among animals at
large. But of this matter I shall have more to
say immediately.
Meantime, however, that we may come to
the parts subservient to generation, as Fabri-
cius says, "let us consider and perpend in what
order the organs subserving generation are pro-
duced— which are formed first, which last. In
this investigation two bases are to be laid, one
having reference to the corporeal, the other to
the incorporeal; that is to say, to nature and
the vital principle. The corporeal base," he con-
tinues, "I call that which depends on and pro-
ceeds from the nature of the body, and of which
illustrations are readily supplied from things
made by art; as for example, that every build-
ing requires a foundation upon which it may be
established and reared; from whence walls are
raised, by which both floors and ceilings are
supported; then are all the supplementary
parts added and ornaments appended: and so,
in fact, does Nature strive in the construction
of the animal body ; for first she forms the bones
444
WILLIAM HARVEY
as a foundation, in order that all the parts of
the body may grow upon and be appended to
and established around them. These are the
parts, in other words, that are first formed and
solidified; for as the bones derive their origin
from a very soft and membranous substance,
and by and by become extremely hard, much
time is required to complete the formation of a
bone, and it is therefore that they are first pro-
duced. Hence Galen did not compare the forma-
tion of the animal body to every kind of artifi-
cial structure, but particularly to a ship; for he
says, as the commencement and foundation of
a ship is the keel, from which the ribs, circular-
ly curved, proceed on either side at moderate
distances from each other, like the sticks of a
hurdle, in order that the whole fabric of the
vessel may afterwards be reared upon the keel
as a suitable basis; so in the formation of the
animal body does Nature, by means of the out-
stretched spine and the ribs drawn around it,
secure a keel and suitable foundation for the
entire superstructure, which she then raises and
perfects."1
But experience teaches us that all this is very
different in fact, and that the bones are rather
among the last parts to be formed. The bones of
the extremities and skull, and the teeth, do not
arise any sooner than the brain, the muscles,
and the other fleshy parts: in new-born foetuses,
perfect in other respects, the place of the bones
is supplied by mere membranes or cartilages,
which are only subsequently and in the lapse of
time converted into bones; a circumstance
which sufficiently appears in the crania of new-
born infants, and in the state of their ribs and
articulations.
And although it be true that the first rudi-
ments of the body are seen in the guise of a re-
curved keel, still this is a soft mucous and jelly-
like substance, which has no affinity in nature,
structure, or office to bone; and although cer-
tain globules depend from thence, the destined
rudiments of the head, still these contain no
solid matter, but are mere vesicles full of limpid
water, which are afterwards formed into the
brain, cerebellum, and eyes, which are all sub-
sequently surrounded by the skull, at a period,
however, when the beak and nails have already
acquired consistency and hardness.
This view of Fabricius is therefore both im-
perfect and incorrect; inasmuch as he does not
think of what Nature performs in fact in the
work of generation, so much as of what in his
opinion she ought to do, betrayed into this by
1 Op. supra ctt.> p. 43.
his comparison with the edifice reared by art.
As if nature had imitated art, and not rather
art nature! — mindful of which he himself says
afterwards: "It were better to say that art
learned of Nature, and was an imitator of her
doings; for, as Galen everywhere reminds us,
Nature is both older and displays greater wis-
dom in her works than art.*'2
And then when we admit that the bones are
the foundation of the whole body, without
which it could neither support itself nor per-
form any movement, it is still sufficient if they
arise simultaneously with the parts that are
attached to them. And indeed the things that
are to be supported not yet existing, the sup-
ports would be established in vain. Nature,
however, does nothing in vain; nor does she
form parts before there is a use for them. But
animals receive their organs as soon as the of-
fices of these are required. The first basis of
Fabricius, therefore, is distinctly overthrown
by his own observations on the egg, and the
comparison drawn by Galen.
He appears to have come nearer the truth
where he says: "The other basis of the parts to
be formed first or last is obtained from nature,
that is, from the vital principle by which the
animal body is ruled and directed. If there be
two grades of this principle, the vegetative and
animal, the vegetative must be held prior in
point of nature and time, inasmuch as it is com-
mon to plants and animals; and assuredly the
organs officiating in the vegetative office will
be engendered and formed before those that
belong to the sensitive and motive principle,
especially to the chief organs which are in im-
mediate relationship with the governing prin-
ciple. Now these organs are two in especial —
the liver and the heart: the liver as seat of con-
cupiscence, of the vegetative or nutritive fac-
ulty; the heart, as the organ whose heat main-
tains and perfects the vegetative and every
other faculty, and in this way has most intimate
connexions and relations with the vegetative
force. Whence, if after the third day you see
the heart palpitating in the point where the
chick is engendered, as Aristotle bears witness
to the fact that you can, you will not be sur-
prised but rather be disposed to admit that the
heart belongs to the vegetative degree and
exists for its sake. It is also consonant with rea-
son that the liver should be engendered simul-
taneously with the heart, but should lie perdue
or hidden, as it does not pulsate. And Aristotle
himself admits that the heart and liver exist in
2 Op. tit.> p. 44.
ANIMAL GENERATION
445
the animal body for similar reasons; so that
where there is a heart there also is a liver dis-
covered. If the heart and liver be the parts first
produced, then, it is also fair to suppose that
the other organs subserving these two should
be engendered in the same manner — the lungs
which exist for the sake of the heart; and, for
the sake of the liver, almost all the viscera
which present themselves in the abdomen."1
Still is all this very different from the se-
quence we witness in the egg. Nor is it true
that the liver is engendered simultaneously
with the heart; nor does the salve avail with
which he would cover that infirmity where he
says that the liver is concealed because it does
not palpitate; for the eyes and vena cava and
carina are all conspicuous enough from the
commencement, although none of them palpi-
tate. How come the liver and lungs, if they be
then extant, to be visible without any palpi-
tation? And then Fabricius himself has indi-
cated a minute point situated in the centre of
his figure of the chick of the fourth day, with-
out stating, however, that it had any pulsation;
and this he did not perceive to be the heart,
but rather believed it to be the rudiment of the
body. It is certain, therefore, that Fabricius
spoke only from conjecture and preconceived
opinion of the origin of the liver; even in the
same way as others have done, Aldrovandus
and Parisanus among the number, who, light-
ing upon two points, and perceiving that they
did not pulsate simultaneously, straightway
held that one was the heart, the other the liver.
As if the liver ever pulsated, and these two
points were aught but the two pulsating vesi-
cles replying to each other by alternate con-
tractions, in the way and manner we have in-
dicated in our history !
Fabricius, therefore, is either deceived or
deceives, when he says, "In the first stage of
the production of the chick, the liver, heart,
veins, arteries, lungs, and all the organs con-
tained in the cavity of the abdomen, are en-
gendered together; and in like manner are the
carina, in other words, the head with the eyes
and entire vertebral column and thorax en-
gendered." For the heart, veins, and arteries
are perfectly distinguished some time before the
carina; the carina, again, is seen before the eyes;
the eyes, beak, and sides before the organs con-
tained in the cavity of the abdomen; the stom-
ach and intestines before the liver or lungs;
and there are still other particulars connected
with the order of production of the parts in
1 Op. tit. ut. sup.
generation, of which we shall speak by and by.
He is also mistaken when he would have the
vegetative portion of the vital principle prior
in nature and time to the sensitive and motive
element. For that which is prior in nature is
mostly posterior in the order of generation. In
point of time, indeed, the vegetative principle
is prior; because without it the sensitive prin-
ciple cannot exist: an act— if the act of an or-
ganic body — cannot take place without or-
gans; and the sensitive and motive organs are
the work of the vegetative principle; the sensi-
tive soul before the existence of action, is like a
triangle within a quadrangle. But nature in-
tended that that which was primary and most
noble should also be primary; wherefore the
vegetative force is by nature posterior in point
of order, as subordinate and ministrative to the
sensitive and motive faculties.
EXERCISE 55. Of (he order of the parts according
to Aristotle
The following appear to be Aristotle's views
of the order of generation: "When conception
takes place, the germ comports itself like a seed
sown in the ground. For seeds likewise contain
a first principle, which, existing in the begin-
ning in potentia, by and by when it manifests
itself, sends forth a stem and a root, by which
aliment is taken up; for increase is indispensable.
And so in a conception, in which all the parts
of the body inhere in potentia, and the first
principle exists in a state of special activity."2
This principle in the egg — the body anal-
ogous to the seed of a vegetable — we have
called with Fabricius the spot or cicatricula,
and have spoken of it as a very primary part of
the egg, as that in which all the other parts in-
here in potentia, and from whence each in its
order afterwards arises. In this spot, in fact, is
contained that— whatever it may be— by
which the egg is made productive; and here is
the first action of the formative faculty, the
first effect of the vegetative heat revealed.
This spot, as we have said, dilates from the
very commencement of the incubation, and ex-
pands in circles, in the centre of which a
minute white speck is displayed, like the shin-
ing point in the pupil of the eye; and here anon
is discovered the punctum saliens rubrum,
with the ramifications of the sanguiferous ves-
sels, and this as soon as the fluid, which we have
called the colliquament, has been produced.
"Wherefore," adds Aristotle,3 "the heart is
2 On the Generation of Animals, n. 4.
446
WILLIAM HARVEY
the first part perceived in fact; and this is in
conformity not only with sense, but also with
reason. For as that which is engendered is al-
ready disjunct and severed from both parents,
and ought to rule and regulate itself like a son
who comes of age and has his separate establish-
ment, it must therefore possess a principle, an
intrinsic principle, by which the order of the
members may be subsequently determined,
and whatever is necessary to the constitution
of a perfect animal arranged. For if this prin-
ciple were at any time extrinsic, and entered
into the body at a subsequent period, you
would not only be in doubt as to the time at
which it entered, but as every part is distinct,
you would also see it as necessary that that
should first exist from which the other parts de-
rive both increase and motion." The same
writer elsewhere1 asserts: "This principle is a
portion of the whole, and not anything added,
or included apart. For," he proceeds,"the
generation of the animal completed, does this
principle perish, or does it continue ? But noth-
ing can be shown existing intrinsically which is
not a part of the whole organized being, wheth-
er it be plant or animal; wherefore it would be
absurd to maintain that the principle in ques-
tion perished after the formation either of any
one or of any number of parts; for what should
form those that were not yet produced ? Where-
fore," he continues further, "they say not well
who with Democritus assert that the external
parts of animals are those first seen, and then
the internal parts, as if they were rearing an ani-
mal of wood and stone, for such a thing would
include no principle within itself. But all ani-
mals have and hold a principle in their interior.
Wherefore the heart is seen as the first distinct
part in animals that have blood; for it is the
origin of all the parts, whether similar or dissim-
ilar; and the creature that begins to feel the
necessity of nourishment, must already be pos-
sessed by the principle of an animal and a full-
grown foetus."
From the above, it clearly appears that Aris-
totle recognizes a certain order and commence-
ment in animal generation, namely, the heart,
which he regards as the first produced and first
vivified part of the animal, and, like a son set
free from the tutelage of his parents, as self-
sufficing and independent, whence not only
does the order of the parts proceed, but as that
by which the animal itself is maintained and
preserved, receiving from it at once life and
sustenance, and everything needful to the per-
1 Ibid, ii. i.
fection of its being. For as Seneca says: "In the
semen is comprised the entire cause of the fu-
ture man; and the unborn babe has written
within it the law of a beard and a hoary head.
For the whole body and the load of future
years are already traced in delicate and obscure
outlines in its constitution."2
We have already determined whether the
heart were this primigenial part or not; in
other words, whether Aristotle's words refer to
that part which, in the dissection of animals, is
seen sooner than all the rest, the punctum
saliens, to wit, with its vessels full of blood; and
we have cordially assented to an answer in the
affirmative. For I believe that the blood, to-
gether with its immediate instruments, the um-
bilical vessels, by which, as by roots, nutriment
is attracted, and the pulsating vesicles, by
which this nutriment is distributed, to main-
tain life and growth in every other part, are
formed first and foremost of all. For as Aris-
totle3 has said, it is the same matter by which a
thing grows, and by which it is primarily con-
stituted.
Many, however, err in supposing that dif-
ferent parts of the body require different kinds
of matter for their nourishment. As if nutrition
were nothing more than the selection and at-
traction of fit aliment; and in the several parts
of the body to be nourished, no concoction, as-
similation, apposition, and transmutation were
required. This as we learn, was the opinion of
Anaxagoras of old :
Who held the principles of things to be
Homoeomeric\—bone to be produced
Of small and slender bones; the viscera
Of small and slender viscera; the blood
Of numerous associate drops of blood*
But Aristotle, with the greatest propriety,
observes: "Distinction of parts is not effected,
as some think, by like being carried by its na-
ture to like; for, besides innumerable difficulties
belonging to this opinion in itself, it happens
that each similar part is severally created; for
example, the bones by themselves, the nerves,
the flesh, &c."6 But the nourishment of all parts
is common and homogeneous, such as we see the
albumen to be in the egg, not heterogeneous
and composed of different parts. Wherefore all
we have said of the matter from which parts are
made, is to be stated of that by which they in-
2 Nat. Quxst. iii. 29.
8 On the Generation of Animals^ n. 4.
4 Lucretius, On the Nature of Things, i. 834-838.
B Loc. sup. tit.
ANIMAL GENERATION
447
crease: all derive nourishment from that in
which they exist in potentia, though not in act.
Precisely as from the same rain plants of every
kind increase and grow; because the moisture
which was a like power in reference to all, be-
comes actually like to each when it is changed
into their substances severally: then does it ac-
quire bitterness in rue, sharpness in mustard,
sweetness in liquorice, and so on.
He explains, moreover, what parts are en-
gendered before others, and assigns a reason
which does not differ from the second basis of
Fabricius. "The cause by which, and the cause
of this cause, are different; one is first in genera-
tion, the other in essence"; by which we are to
understand that the end is prior in nature and
essence to that which happens for the sake of
the end ; but that which happens for the sake of
the end must be prior in generation. And on
this ground Fabricius rightly infers that all
those parts which minister to the vegetative
principle are engendered before those that
serve the sensitive principle, inasmuch as the
former is subordinate to the latter.
He subsequently adds the differences of those
parts which are made for some special purpose:
some parts, for example, are instituted for a
purpose by nature, because this purpose ensues;
and others because they are instruments which
the purpose employs. The former he designates
genitalia^ the latter instrumenta. For the end or
purpose, he says, in some cases, is posterior, in
others prior to that which is its cause. For both
the generator and the instruments it uses must
exist anteriorly to that which is engendered by
or from them. The parts serving the vegetative
principle, therefore, are prior to the parts which
are the ministers of sense and motion. But the
parts dedicated to motion and sensation are
posterior to the motive and sensitive faculties,
because they are the instruments which the
motive and sensitive faculties employ. For it is
a law of nature that no parts or instruments be
produced before there be some use for them,
and the faculty be extant which employs them.
Thus there is neither any eye nor any motive
organ engendered until the brain is produced,
and the faculties pre-exist which are to see and
to govern motion.
In like manner, as the pulsating vesicles serve
as instruments for the motion of the blood, and
the heart in its entire structure does the same
(as I have shown in the work On the Motion of
the Blood), urging the blood in a ceaseless round
through every part of the body, we see that the
blood must exist before the heart, both in the
order of generation and of nature and essence.
For the blood uses the heart as an instrument,
and moreover, when engendered it continues to
nourish the organ by means of the coronary
arteries, distributing heat, spirits, and life to it
through their ramifications.
We shall have further occasion to show from
an entire series of anatomical observations, how
this rule of Aristotle in respect of the true pri-
ority of the parts is borne out. Meantime we
shall see how he himself succeeds in duly in-
ferring the causes of priority in conformity with
his rule.
"After the prime part — viz., the heart — is
engendered," he says, "the internal parts are
produced before the external ones, the superior
before the inferior; for the lower parts exist for
the sake of the superior, and that they may
serve as instruments, after the manner of the
seeds of vegetables, which produce roots sooner
than branches."
Nature, however, follows no such order in
generation; nor is the instance quoted invari-
ably applicable; for in beans, peas, and other
leguminous seeds, in acorns, also, and in grain,
it is easy to see that the stem shoots upwards
and the root downwards from the same germ;
and onions and other bulbous plants send off
stalks before they strike root.
He then subjoins another cause of this order,
viz.: "That as Nature does nothing in vain or
superfluously, it follows that she makes nothing
either sooner or later than the use she has for it
requires." That is to say, those parts are first
engendered whose use or function is first re-
quired; and some are begun at an earlier period
because a longer time is requisite to bring them
to perfection; and that so they may be in the
same state of forwardness at birth as those that
are more rapidly produced. Just as the cook,
having to dress certain articles for supper, which
by reason of their hardness are done with diffi-
culty, or require gentle boiling for a great length
of time, these he puts on the first, and only
turns subsequently to those that are prepared
more quickly and with less expenditure of heat;
and further, as he makes ready the articles that
are to come on in the first course first of all,
and those that are to be presented in the second
course afterwards; so also does Nature in the
generation of animals only proceed at a later
period to the construction of the soft and moist
and fleshy parts, as requiring but a short time
for their concoction and formation, whilst the
hard parts, such as the bones, as requiring ample
evaporation and abundant drying, and their
WILLIAM HARVEY
matter long remaining inconcoct, she proceeds
to fashion almost from the very beginning.
"And the same thing obtains in the brain," he
adds, "which, large in quantity and exceedingly
moist at first, is by and by better concocted and
condensed, so that the brain as well as the eye
diminishes in size. The head is, therefore, very
large at first, in comparison with the rest of the
body, which it far surpasses because of the brain
and the eyes, and the large quantity of mois-
ture contained in them. These parts, neverthe-
less, are among the last to be perfected, for the
brain acquires consistence with difficulty, and
it is long before it is freed from cold and mois-
ture in any animal, and especially in man. The
sinciput, too, is consolidated the last, the bones
here being quite soft when the infant sees the
light."
He gives another reason, viz., because the
parts are formed of different kinds of matter:
"Every more excellent part, the sharer in the
highest principle is, further, engendered from
the most highly concocted, the purest and first
nutriment; the other needful parts, produced
for the sake of the former, from the worse and
excrementitious remainder. For Nature, like the
sage head of a family, is wont to throw away
nothing that may be turned to any useful pur-
pose. But he still regulates his household so that
the best food shall be given to his children, the
more indifferent to his menials, the worst to the
animals. As then, man's growth being complete
and mind having been superadded (in other
words, and, as I interpret the passage, adult man
having acquired sense and prudence), things
are ordered in this way, so does Nature at the
period of production even compose the flesh
and the other more sensitive parts of the purest
matter. Of the excrementitious remainder she
makes the bones, sinews, hair, nails, and other
parts of the same constitution. And this is the
reason why this is done last of all, when Nature
has an abundant supply of recrementitious ma-
terial." Our author then goes on to speak of "a
twofold order of aliment": "one for nutrition,
another for growth"; "the nutritive is the one
which supplies existence to the whole and to
the parts; the augmentative, that which causes
increase to the bulk."
This is in accordance with what we find in
the egg, where the albumen supplies a kind of
purer aliment adapted to the nutrition of the
embryo in its earlier stages, and the yelk affords
the material for the growth of the chick and
pullet. The thinner albumen, moreover, as we
have seen, is used in fashioning the first and
more noble parts; the thicker albumen and the
yelk, again, are employed in nourishing and
making these to grow, and further in forming
the less important parts of the body. "For," he
says, "the sinews, too, are produced in the same
way as the bones, and from the same material,
viz. : the seminal and nutritive excrementitious
matter. But the nails, hair, horns, beak, and
spurs of birds, and all other things of the same
description, are engendered of the adventitious
and nutritive aliment, which is obtained both
from the mother and from without." And then
he gives a reason why man, whilst other ani-
mals are endowed by nature with defensive and
offensive arms, is born naked and defenceless,
which is this: that whilst in the lower animals
these parts are formed of remainders or excre-
ments, man is compounded of a purer material,
"which contains too small a quantity of incon-
coct and earthy matter."
Thus far have we followed Aristotle on the sub-
ject of "The Order in Generation," the whole of
which seems to be referrible to one principle,
viz.: the perfection of Nature, who in her
works does nothing in vain and has no short-
comings, but still does that in the best manner
which was best to be done. Hence in generation
no part would either precede or follow, did she
prefer producing them altogether, viz. : in cir-
cumstances where she acts freely and by elec-
tion; for sometimes she works under compul-
sion, as it were, and beside her purpose, as when
through deficiency or superabundance of ma-
terial, or through some defect in her instru-
ments, or is hindered of her ends by external
injuries. And thus it occasionally happens that
the final parts are formed before the instrumen-
tal parts — understanding by final parts, those
that use others as instruments.
And as some of the parts are genital, nature
making use of them in the generation of other
parts, as the means of removing obstacles the
presence of which would interfere with the due
progress of the work of reproduction, and others
exist for other special ends; it therefore hap-
pens that for the disposition of material, and
other requisites, some parts are variously en-
gendered before others, some of them being
begun earlier but completed at a later period,
some being both begun and perfected at an
earlier period, and others being begun together
but perfected at different times subsequently.
And then the same order is not observed in the
generation of all animals, but this is variously
altered; and in some there is nothing like suc-
cession, but all the parts are begun and per-
ANIMAL GENERATION
449
fectcd simultaneously, by metamorphosis, to
wit, as has been already stated. Hence it fol-
lows, in fine, that the primogenate part must
be of such a nature as to contain both the be-
ginning and the end, and be that for whose sake
all the rest is made, namely, the living principle,
or soul, and that which is the potential and
genital cause of this, the heart, or in our view
the blood, which we regard as the prime seat of
the soul, as the source and perennial centre of
life, as the generative heat, and indeed as the
inherent heat; in a word, the heart is the first
efficient of the whole of the instrumental parts
that are produced for the ends of the soul, and
used by it as instruments. The heart, according
to Aristotle, I say, is that for which all the parts
of animals are made, and it is at the same time
that which is at once the origin and fashioner of
them all.
EXERCISE 56. Of the order of the parts in generation
as it appears from observation
That we may now propose our own views of
the order of the parts in generation as we have
gathered it from our observations, it appears
that the whole business of generation in all ani-
mals may be divided into two periods, or con-
nected with two structures: the ovum, i. e., the
conception and seed, or that, whatever it be,
which in spontaneous productions corresponds
to the seed, whether with Fernelius it be called
"the native celestial heat in the primogenial
moisture," or with Aristotle, "the vital heat in-
cluded in moisture." For the conception in
viviparous animals, as we have said, is analogous
to the seed and fruit of plants; in the same way
as it is to the egg of oviparous creatures; to
worms in spontaneously engendered animals, or
to certain vesicles fruitful by the vital warmth
of their included moisture. In each and all of
these the same things inhere which might with
propriety lead to their being called seeds; they
are all bodies, to wit, from which and by which,
as previously existing matter, artificer and or-
gan, the whole of an animal body is primarily
engendered and produced.
The other structure is the embryo produced
from the seed or conception. For both the mat-
ter and the moving and efficient cause, and the
instruments needful to the operation, must
necessarily precede operation of any and every
kind.
We have already examined the structure of
the egg. Now the embryo to which it gives
birth, in so far as this can be made out by ob-
servation and dissection, particularly among
the more perfect animals with blood, appears to
be perfected by four principal degrees or proc-
esses, which we reduce to as many orders, in
harmony with the various epochs in generation;
and we shall demonstrate that what transpires
in the egg also takes place in every conception
or seed.
The first process is that of the primogenial
and genital part, viz., the blood with its recep-
tacles, in other words, the heart and its vessels.
And this part is first engendered for two
principal reasons: ist, because it is the principal
part which uses all the rest as instruments, and
for whose sake the other parts are formed; and,
2d, because it is the prime genital part, the
origin and author of the rest. The part, in a
word, in which inhere both the principle whence
motion is derived, and the end of that motion,
is obviously father and sovereign.
In the generation of this first part, which in
the egg is accomplished in the course of the
fourth day, although I have not been able to
observe any order or sequence, inasmuch as the
whole of its elements — the blood, the vessels,
and the pulsating vesicles — appear simultane-
ously, I have nevertheless imagined, as I have
said, that the blood exists before the pulse, be-
cause, according to nature's laws, it must be
antecedent to its receptacles. For the substance
and structure of the heart, namely, the conical
mass with its auricles and ventricles, as they are
produced long subsequently along with the
other viscera, so must they be referred to the
same class of parts as these, namely, the third.
In the production of the circulating system
the veins are sooner seen than the arteries; such
at least is our conclusion.
The second process, which begins after the
fourth day, is indicated by a certain concres-
cence, which I designate vermiculum — worm or
maggot; for it has the life and obscure motions
of a maggot; and as it concretes into a mucous
matter, it divides into two parts, the larger and
superior of which is seen to be conglobed, and
divided, as it were, into thin vesicles— the
brain, the cerebellum, and the two eyes; the
less, again, constituting the carina, arises over
the vena cava and extends in the line of its
direction.
In the genesis of the head, the eyes are first
perceived; by and by a white point makes its
appearance in the situation of the beak, and the
slime drying around it, it becomes invested
with a membrane.
The outline of the rest of the body follows
about the same period. First, from the carina
450
WILLIAM HARVEY
something like the sides of a ship are seen to
arise; the parts having an uniform consistence
in the beginning, but the ribs being afterwards
Erefigured by means of extremely fine white
nes. The instruments of locomotion next arise
—the legs and wings; and the carina and the
extremities adnate to it are then distinguished
into muscles, bones, and articulations.
These two rudiments of the head and trunk
appear simultaneously, but as they grow and
advance to perfection subsequently, the trunk
increases and acquires its shape much more
speedily than the head; so that this, which in
the first instance exceeded the whole trunk in
size, is now relatively much smaller. And the
same thing occurs in regard to the human
embryo.
The same disparity also takes place between
the trunk and the extremities. In the human
embryo, from the time when it is not longer
than the nail of the little finger, till it is of the
size of a frog or mouse, the arms are so short
that the extremities of the fingers could not
extend across the breast, and the legs are so
short that were they reflected on the abdomen
they would not reach the umbilicus.
The proportion of the body to the extremi-
ties in children after their birth continues ex-
cessive until they begin to stand and run. In-
fants, therefore, resemble dwarfs in the begin-
ning, and they creep about like quadrupeds, at-
tempting progressive motion with the assist-
ance of all their extremities; but they cannot
stand erect until the length of the leg and thigh
together exceeds the length of the rest of the
body. And so it happens, that when they first
attempt to walk, they move with the body
prone, like the quadruped, and can scarcely
rise so erect as the common dunghill fowl.
And so it happens that among adult men the
long-legged— they who have longer legs, and
especially longer thighs—are better walkers,
runners, and leapers than square-built, compact
men.
In this second process many actions of the
formative faculty are observed following each
other in regular order (in the same way as we
see one wheel moving another in automata, and
other pieces of mechanism), and all arising from
the same mucaginous and similar matter. Not
indeed in the manner that some natural philoso-
phers would have it when they say "that like is
carried to its like." We are rather to maintain
that parts are moved, not changing their places,
but remaining and undergoing change in hard-
ness, softness, colour, &c., whence the diversi-
ties between similar parts; those things appear-
ing in act which were before in power.1 The ex-
tremities, spine, and rest of the body, namely,
are formed, grow, and acquire outline and com-
plexion together; the extremities, comprising
bones, muscles, tendons, and cartilages, all of
which on their first appearance were similar
and homogeneous, become distinguished in
their progress, and, connected together, com-
pose organs, by whose mutual continuity the
whole body is constituted. In like manner, the
membrane growing around the head, the brain
is composed, and the lustrous eyes receive their
polish out of a perfectly limpid fluid.
That is to say, Nature sustains and augments
the several parts by the same nourishment with
which she fashioned them at first, and not, as
many opine, with any diversity of aliment and
particles similar to each particular structure.
As she is increasing the mucaginous mass or
maggot, like a potter she first divides her ma-
terial, and then indicates the head and trunk
and extremities; like a painter, she first sketches
the parts in outline, and then fills them in with
colours; or like the shipbuilder, who first lays
down his keel by way of foundation, and upon
this raises the ribs and roof or deck: even as he
builds his vessel does Nature fashion the trunk
of the body and add the extremities. And in
this work she orders all the variety of similar
parts— the bones, cartilages, membranes, mus-
cles, tendons, nerves, &c.— from the same pri-
mary jelly or mucus. For thick filaments are
produced in the first instance, and these by and
by are brought to resemble cords; then they
are rendered cartilaginous and spinous; and,
lastly, they are hardened and concocted into
bones. In the same way the thicker membrane
which invests the brain is first cartilaginous and
then bony, whilst the thinner membrane mere-
ly consolidates into the pericranium and integ-
ument. In similar order flesh and nerve from
soft mucus are confirmed into muscle, tendon,
and ligament; the brain and cerebellum are con-
densed out of a perfectly limpid water into a
firm coagulum; for the brain of infants, before
the bones of the head have closed, is soft and
diffluent, and has no greater consistence than
the curd of milk.
The third process is that of the viscera, the
formation of which in the chick takes place
after the trunk is cast in outline, or about the
sixth or seventh day — the liver, lungs, kidneys,
cone and ventricles of the heart, and intestines,
all become visible nearly at the same moment;
1 On the Generation of Animals, n. 4.
ANIMAL GENERATION
451
they appear to arise from the veins, and to be
connected with them in the same way as fungi
grow upon the bark of trees. They are, as I have
already said, gelatinous, white, and bloodless,
until they take on their proper functions. The
stomach and intestines are first discovered as
white and tortuous filaments extending length-
wise through the abdomen; along with these
the mouth appears, from which a continuous
canal extends to the anus, and connects the
superior with the inferior parts. The organs of
generation likewise appear about the same time.
Up to this period all the viscera, the intes-
tines, and the heart itself inclusive, are excluded
from the cavities of the body and hang pendu-
lous without, attached as it were to the veins.
The trunk of the body presents itself, in fact,
like a boat undecked or a house without a roof,
the anterior walls of the thorax and abdomen
not being yet extant to close these cavities.
But as soon as the sternum is fashioned the
heart enters into the chest as into a dwelling
which it had built and arranged for itself; and
there, like the tutelary genius, it enters on the
government of the surrounding mansion, which
it inhabits with its ministering servants the
lungs. The liver and stomach are by and by in-
cluded within the hypochondria, and the intes-
tines are finally surrounded by the abdominal
parietes. And this is the reason wherefore with-
out dissection the heart can no longer be seen
pulsating in the hen's egg after the tenth day of
incubation.
About this epoch the point of the beak and
the nails appear of a fine white colour; a quanti-
ty of chylous matter presents itself in the stom-
ach; a little excrement is also observed in the
intestine, and the liver being now begun, some
greenish bile is perceived; facts from which it
clearly appears that there is another digestion
and preparation of nutriment going on besides
that which takes place by the branches of the
umbilical veins; and it is reasonable matter of
doubt how the bile, the excrementitious matter
of the second digestion, can be separated by the
instrumentality of the liver from the other
humours, when we see it produced at the same
time as this organ.
In the order now indicated are the internal
organs generated universally; in all the animals
which I have dissected, particularly the more
perfect ones, and man himself, I have found
them produced in the same manner: in these,
in the course of the second, third, and fourth
month, the heart, liver, lungs, kidneys, spleen,
and intestines present themselves inchoate and
increasing, and all alike of the same white col-
our which belongs to the body at large. Where-
fore these early days are not improperly spoken
of as the days when the embryo is in the milfy
for with the exception of the veins, particularly
those of the umbilicus, everything is as it were
spermatic in appearance.
I am of opinion that the umbilical arteries
arise after the veins of the same name, because
the arteries are scarcely to be discovered in the
course of the first month, and take their rise
from the branches that descend to either lower
extremity. I do not believe, therefore, that
they exist until that part of the body whence
they proceed is formed. The umbilical veins, on
the contrary, are conspicuous long before any
part of the body is begun.
What I have now said I have derived from
numerous dissections of human embryos of al-
most every size; for I have had them for inspec-
tion from the time they were like tadpoles, till
they were seven or eight fingers* breadth in
length, and from thence onwards to the full
time. I have examined them more particularly,
however, through the second, third, and fourth
months, in the course of which the greatest
number of changes take place, and the order of
development is seen with greatest clearness.
In the human embryo, then, of the age of two
months, what we have spoken of as taking
place in the "second process/' is observed to
occur. For I rather think that during the first
month there is scarcely anything of the concep-
tion in the uterus— at all events, I have never
been able to discover anything. But the first
month past, I have repeatedly seen conceptions
thrown off, and similar to the one which Hip-
pocrates mentions as having been voided by the
female pipe-player, of the size of a pheasant's
or pigeon's egg. Such conceptions resemble an
egg without its shell; they are, namely, of an
oval figure; the thicker membrane or chorion
with which they are surrounded, however, is
seen to be covered with a white mucor exter-
nally, particularly towards the larger end; in-
ternally it is smooth and shining, and is filled
with limpid and sluggish water — it contains
nothing else.
In the course of the second month I have fre-
quently seen an ovum of this description, or
somewhat larger, thrown off with the symp-
toms of abortion, viz., ichorous lochia; the ovum
being sometimes entire, at other times burst,
and covered with bloody coagula. Within it
was smooth and slippery; it was covered with
adhering blood without. Its form was that which
452
WILLIAM HARVEY
I have just described. In some of these aborted
ova, I have discovered embryos, in others I
could find none. The embryo, when present,
was of the length of the little finger-nail, and
in shape like a little frog, save that the head was
exceedingly large and the extremities very
short, like a tadpole in the month of June, when
it gets its extremities, loses its tail, and assumes
the form of a frog. The whole substance was
white, and so soft and mucilaginous, that un-
less immersed in clear water, it was impossible
to handle it. The face was the same as that of
the embryo of one of the lower animals — the
dog or cat, for instance, without lips, the mouth
gaping, and extending from ear to ear.
Many women, whose conceptions, like the
wind eggs of fowls, are barren and without an
embryo, miscarry in the third month.
I have occasionally examined aborted ova of
this age, of the size of a goose's egg, which con-
tained embryos distinct in all their parts, but
misshapen. The head, eyes, and extremities
were distinct, but the muscles were indistinct;
there were no bones, but certain white lines in
their situations, and as it seemed, soft cartilages.
The substance of the heart was extremely white,
and consisted of two ventricles of like size and
thickness of walls, forming a cone with a double
apex, which might be compared to a small twin-
kernel nut. The liver was very small and of the
general white colour. Through the whole of
this time, i.e., during the first three months,
there is scarcely any appearance of a placenta
or uterine cake.
In every conception of this description I have
seen, I have always found a surrounding mem-
brane containing a large quantity of watery
fluid, between which and the body of the em-
bryo, suspended by its middle by means of a
long and twisted umbilical cord, there is such
disproportion, that it is impossible to regard
this liquid as either sweat or urine; it seems far
more probable that like the colliquament in the
hen's egg, it is a fluid destined by nature for the
nourishment of the foetus. Nor was there any
indication to be discovered of these concep-
tions or ova having been connected with the
uterus; there was only on the external surface
of their larger extremity a greater appearance
of thickening and wrinkling, as if the rudiments
of the future placenta had existed there.
These conceptions, therefore, appear to me
in the light of ova, which are merely cherished
within the uterus, and, like the egg in the uter-
us of the fowl, grow by their own inherent
powers.
In the fourth month, however, it is wonder-
ful to find what rapid strides the foetus has
made: from the length of the thumb it has now
grown to be a span long. All the members, too,
are distinct and are tinged with blood; the bones
and muscles can be distinguished ; there are ves-
tiges of the nails, and the foetus now begins to
move lustily. The head, however, is excessively
large; the face without lips, cheeks, and nose;
the gape of the mouth is enormous, and the
tongue lies in its middle; the eyes are small,
without lids to cover them; the middle integu-
ment of the regions of the forehead and sinciput
is not yet cartilaginous, far less bony; but the
occiput is somewhat firm and in some sort carti-
laginous, indicating that the skull already be-
gins to acquire solidity.
The organs of generation have now made
their appearance, but the testes are contained
within the abdomen, in the situation of the fe-
male uterus, the scrotum still remaining empty.
The female organs are yet imperfect, and the
uterus with its tubes resembles the two-horned
uterus of the lamb.
The placenta, of larger size, and now attached
to the uterus, comprises nearly one half of the
entire conception, and presented itself to my
eye as a fleshy or fungous excrescence of the
womb, so firmly was its gibbous portion con-
nected all around with the uterine walls, which
had now grown to greater thickness. The
branches of the umbilical vessels struck into the
placenta like the roots of a tree into the ground,
and by their means was the conception now,
for the first time, connected with the uterus.
The brain presented itself as a large and soft
coagulum, full of ample vessels. The ventricles
of the heart were of equal capacity, and their
walls of the same thickness. In the thorax, and
covered by the ribs, three cavities, nearly of the
same dimensions, were perceived; of these the
lowest was occupied by the lungs, which are
full of blood, and of the same colour as the liver
and kidneys; the middle cavity was filled by
the heart and pericardium; the superior cavity,
again, was possessed by the gland called the
thymus, which is now of very ample size.
In the stomach there was some chyle discov-
ered, not very different in character from the
fluid in which the embryo swam. It also con-
tained some white curdled matter, not unlike
the mucous sordes which the nurse washes par-
ticularly from between the folds of the skin of
new-born infants. In the upper part of the in-
testines there was a small quantity of excre-
mentitious or chylous matter; the lower bowels
ANIMAL GENERATION
453
contained meconium. In the urinary bladder
there was urine, and in the gall bladder bile.
The intestinum coecum, that appendix of the
colon, was empty as in the adult, and appar-
ently superfluous, not as in the lower animals —
the hog, horse, hare — constituting, as it were,
another stomach. The omentum, or apron,
floated over the intestines at large like a thin
and transparent veil or cloud.
The kidneys at this epoch are not yet formed
into a smootn and continuous rounded mass, as
in the adult, but are compacted of numerous
smaller masses, as we see them in the calf and
sturgeon, as if there were a renal globule or nip-
ple placed at the extremity of each division of
the ureter, from the orifice of which the urine
distilled. Over the kidneys two bodies, first
observed by Eustachius, are discovered, very
abundantly supplied with blood, so that their
veins, which anatomists designate as venae adi-
posae, are not much smaller than the emulgents
themselves. The liver and spleen, according to
their several proportions, are equally full of
blood.
I may here observe, by the way, that in every
strong and healthy human foetus we every-
where discover milk; it is particularly abundant
in the thymus gland, though it is also found in
the pancreas, through the whole of the mesen-
tery, and in certain lacteal veins and glands, as
it seems, situated between the divisions of the
mesenteric vessels. Moreover, it can be pressed
and indeed sometimes flows spontaneously from
the breasts of newly- born infants, and nurses
imagine that this is beneficial to the infant.
And it clearly appears that this fluid, which
abounds in the ovum, is no excrementitious
matter thrown off by the embryo, nothing like
urine or sweat, because its relative quantity is
diminished as the period of parturition ap-
proaches, when the foetus is, of course, larger,
and, as it consumes a greater quantity of nutri-
ment, accumulates excrementitious matter more
abundantly than it did in the first months of
pregnancy. Let it be added, that the bladder is
at this time distended with urine. For my own
part I have never been able to discover that
conduit for the urine, from the bladder to the
umbilicus, which anatomists describe under the
name of urachus; I have, on the contrary, fre-
quently seen urine escaping by the penis, but
never by any urachus, when the bladder was
pressed upon with the hand.
So much for what I have observed with refer-
ence to the order of the parts in the develop-
ment of the human foetus.
In the fourth and last process the parts of the
lowest state and order are produced, those,
namely, that do not exist as needful to the being
or to the maintenance of the individual, but
only as defences against external injury, as
ornaments, or as weapons of offence.
The outermost part of all, the skin, with its
several appendages, cuticle, hair, wool, feath-
ers, scales, shells, claws, hooves, and other items
of the same description, may be regarded as the
principal means of defence or protection. And
it is well devised by Nature, who, indeed, never
does aught amiss, that these parts are the last
to be engendered, inasmuch as they could never
be of use or avail as defences until the animal
was born. The common domestic pullet is,
therefore, born covered with down only, not
with feathers, like certain other birds which
have to be speedily prepared for flight, because
it has to seek its food on foot, not on the wing,
and by active running about hither and thither.
In like manner the young of ducks and geese,
which feed swimming, have their feathers and
wings perfected at a later period than their feet
and legs. It is otherwise with swallows, how-
ever, which have to fly sooner than to walk, be-
cause they feed on the wing.
The down of the pullet begins to appear after
the fourteenth day, the foetus being already
perfect in all its parts. When the feathers first
show themselves, they are in the guise of points
within the skin, but by and by the feathers
project, like plants from the ground, increase
in length, become unfolded, invest the whole
body, and protect it against the inclemencies
of the atmosphere.
Feathers differ from quills in form, use, place
of growth, and order of production. The pullet
is feathered before it has any quills, for the
quill- feathers only grow in the wings and tail,
and also spring more deeply, from the very
lowest part of the integument, or even from
the periosteum, and serve essentially as instru-
ments of motion; the feathers again arise super-
ficially from the skin, and are everywhere pres-
ent as means of protection.
"Nails, hair, horn, and the like," says Aris-
totle,1 "are engendered from the skin; whence
it happens that they change colour with the
skin; for the white and black and particoloured
are so in consequence of the colour of the skin
whence they arise." In the bird, however, this
is not so; for whatever the colour of the feath-
ers, the skin is still never otherwise than of one
tint, viz.) white. And then the same feather or
1 On the Generation of Animals, n. 4.
454
WILLIAM HARVEY
quill is frequently seen of different and often
brilliant colours in different parts for the orna-
ment of the creature.
In the human foetus the skin and all the parts
connected with it are in like manner perfected
the last of all. In the earlier periods, conse-
quently, we find neither lips, cheeks, external
ears, eyelids, nor nose; and the last part to grow
together is the upper lip in the course of the
middle line of the body.
Man comes into the world naked and un-
armed, as if Nature had destined him for a social
creature, and ordained him to live under equi-
table laws and in peace ; as if she had desired
that he should be guided by reason rather than
be driven by force; therefore did she endow
him with understanding, and furnish him with
hands, that he might himself contrive what was
necessary to his clothing and protection. To
those animals to which nature has given vast
strength, she has also presented weapons in har-
mony with their powers; to those that are not
thus vigorous, she has given ingenuity, cun-
ning, and singular dexterity in avoiding injury.
Ornaments of all kinds, such as tufts, crests,
combs, wattles, brilliant plumage, and the like,
of which some vain creatures seem not a little
proud, to say nothing of such offensive weapons
as teeth, horns, spurs, and other implements
employed in combat, are more frequently and
remarkably conferred upon the male than the
female. And it is not uninteresting to remark,
that many of these ornaments or weapons are
most conspicuous in the male at that epoch
when the females come into season, and burn
with desire of engendering. And whilst in the
young they are still absent, in the aged they
also fail as being no longer wanted.
Our common cock, whose pugnacious quali-
ties are well known, so soon as he comes to his
strength and is possessed of the faculty of en-
gendering, is distinguished by his spurs, and
ornamented with his comb and beautiful feath-
ers, by which he charms his mates to the rites of
Venus, and is furnished for the combat with
other males, the subject of dispute being no
empty or vainglorious matter, but the perpet-
uation of the stock in this line or in that; as if
nature had intended that he who could best
defend himself and his, should be preferred to
others for the continuance of the kind. And in-
deed all animals which are better furnished
with weapons of offence, and more warlike than
others, fall out and fight, either in defence of
their young, of their nests or dens, or of their
prey; but more than all for the possession of
their females. Once vanquished, they yield up
possession of these, lay aside their strut and
haughty demeanour, and, crestfallen and sub-
missive, they seem to consume with grief; the
victor, on the contrary, who has gained posses-
sion of the females by his prowess, exults and
boastfully proclaims the glory of his conquest,
Nor is this ornamenting anything adventi-
tious and for a season only; it is a lasting and
special gift of Nature, who has not been studious
to deck out animals, and especially birds only,
but has also thrown an infinite variety of beau-
tiful dyes over the lowly and insensate herb*
and flowers.
EXERCISE 57. Of certain paradoxes and problem*,
to be considered in connexion with this subject
Thus far have we spoken of the order of gen-
eration, whereby the differences between those
creatures that are engendered by metamorpho-
sis and those that are developed by epigenesis,
as well as between those that are said to proceed
from a worm and those that arise from an egg,
have been made to appear. The latter are partly
incorporated from a prepared matter, and are
nourished and increased from a certain remain-
ing matter; the former are incorporated from
the whole of the matter present ; the latter grow
and are formed simultaneously, and after theii
birth continue to wax in size and finally attain
maturity; the former increase at once, and from
a grub or caterpillar grow into an aurelia, and
are then produced, consummately formed, as
butterflies, moths, and the like. Wherefore
Aristotle, as Fabricius1 observes: "As he assigns
a sort of twofold nature to the egg, and a two-
fold egg in this kind, so does he assert a twofold
action and a twofold animal engendered. For,"
he proceeds, "from the first eggs, which are the
primordia of generation, a worm is constantly
produced; viz. : from the eggs of flies, ants, bees,
silkworms, &c., in which some fluid is contained,
and from the whole of which fluid the worm is
engendered; but from the second eggs, formed
by the worms themselves, butterflies are engen-
dered and disclosed, viz.: flying animals con-
tained in a shell, or follicle, or egg, which shell
giving way the winged creature escapes; pre-
cisely as Aristotle2 has it where he speaks of the
egg of the locust." Finally, whilst the higher
animals produced from eggs are perfected by a
succession of parts, the lower creatures that
arise in this way, or that are formed by meta-
morphosis, are produced at one effort, as it were,
1 Fabricius, op. cit., p. 46.
8 History of Animals, v. 28.
ANIMAL, GENERATION
455
and entire. And in the same way are engen-
dered both those creatures that are said to arise
spontaneously, by chance or accident, and de-
rive their first matter or take their origin from
putrefaction, filth, excrement, dew, or the parts
of plants and animals, as well as those that arise
congenerately from the semen of animals. Be-
cause this is common to all living creatures,
viz. : that they derive their origin either from
semen or eggs, whether this semen have pro-
ceeded from others of the same kind, or have
come by chance or something else. For what
sometimes happens in art occasionally occurs in
nature also; those things, namely, take place by
chance or accident which otherwise are brought
about by art. Of this Aristotle1 quotes health as
an illustration. And the thing is not different as
respects the generation, in so far as it is from
seed, of certain animals: their semina are either
present by accident, or they proceed from an
univocal agent of the same kind. For even in
fortuitous semina there is an inherent motive
principle of generation, which procreates from
itself and of itself; and this is the same as that
which is found in the semina of congenerative
animals, — a power, to wit, of forming a living
creature. But of this matter we shall have more
to say shortly.
From what has just been said, however, sev-
eral paradoxes present themselves for considera-
tion. For when we see the cicatricula enlarging
in the egg, the colliquament concocted and pre-
pared, and a variety of other particulars all
tending, not without foresight, to the develop-
ment of the embryo, before the first rudiment
or the merest particle of this is conspicuous,
what should hinder us from believing that the
calidum innatum and the vegetative soul of the
chick are in existence before the chick itself?
For what is competent to produce the effects
and acts of life, except their efficient cause and
principle, heat, namely, and the faculty of the
vegetative soul ? Therefore it would seem that
the soul was not the act of the organic body
possessing life in fotentia; for we regard the
chick with its appropriate form as the conse-
quence of such an act. But where can we sup-
pose the form and vital principle of the chick
to inhere save in the chick itself? unless indeed
we admitted a separation of forms and con-
ceded a certain metamorphosis.
Now this appears most obviously where the
same animal lives, as Aristotle has it, by or un-
der a succession of forms, for example, a cater-
pillar, a chrysalis, a butterfly. For it is of neces-
1 Metafhysics, vu. 9.
sity the same efficient, nutrient, and conserva-
tive principle that possesses each of these, al-
though under different forms; unless we allow
that there is one vital principle in the youth,
another in the man, a third in the aged indi-
vidual, or maintain that the forms of the grub
and caterpillar are the same as those of the silk-
worm and butterfly. Aristotle has entered very
fully into this subject, and we shall ourselves
have more to say on it immediately.
It appears further paradoxical to maintain
that the blood is produced, and moves to and
fro, and is imbued with vital spirits, before any
sanguiferous or locomotive organs are in exist-
ence. Neither is it less new and unheard-of to
assert that sensation and motion belong to the
foetus before the brain is formed; for the foetus
moves, contracting and unfolding itself, when
there is nothing more than a little limpid water
in the place of the brain.
Moreover, the body is nourished and increases
before the organs appropriated to digestion,
viz., the stomach and abdominal viscera, are
formed. Sanguification, too, which is entitled
the second digestion, is perfect before the first,
or chylification, which takes place in the stom-
ach, is begun. The excrementitious products of
the first and second digestions, namely, excre-
ment in the intestines, urine and bile in the
urinary and gall bladder, are contemporaneous
with the existence of the concocting organs
themselves. Lastly, not only is there a soul or
vital principle present in the vegetative part,
but even before this there is inherent mind,
foresight, and understanding, which from the
very commencement to the being and perfect
formation of the chick, dispose and order and
take up all things requisite, moulding them in
the new being, with consummate art, into the
form and likeness of its parents.
In reference to this subject of family likeness,
we may be permitted to inquire as to the reason
why the offspring should at one time bear a
stronger resemblance to the father, at another
to the mother, and, at a third, to progenitors,
both maternal and paternal, farther removed ?
particularly in cases where at one bout, and at
the same moment, several ova are fecundated.
And this too is a remarkable fact, that virtues
and vices, marks and moles, and even particular
dispositions to disease are transmitted by par-
ents to their offspring; and that while some in-
herit in this way, all do not. Among our poultry
some are courageous, and pugnaciously inclined,
and will sooner die than yield and flee from an
adversary; their descendants, once or twice re-
456
WILLIAM HARVEY
moved, however, unless they have come of
equally well-bred parents, gradually lose this
quality; according to the adage, "the brave are
begotten by the brave/* In various other species
of animals, and particularly in the human fam-
ily, a certain nobility of race is observed; nu-
merous qualities, in fact, both of mind and
body, are derived by hereditary descent.
I have frequently wondered how it should
happen that the offspring, mixed in so many
particulars of its structure or constitution, with
the stamp of both parents so obviously upon it,
in so many parts, should still escape all mixture
in the organs of generation; that it should so
uniformly prove either male or female, so very
rarely an hermaphrodite.
Lastly, many things are present before they
appear, and some are begun among the very
first which are completed among the very last,
such as the eyes, the organs of generation, and
the beak.
Several doubts and difficulties have thence
arisen as to the principality and relative dignity
of the several members, in which they who are
fond of such things have displayed their inge-
nuity. Among the number: whether the heart
gives life and virtue to the blood; or, rather,
the blood to the heart. Whether the blood be
extant for the sake of the body as matter, nour-
ishment, and instrument; or, on the contrary,
the body and its parts are the cause of the blood,
and constituted for the sake of the vital prin-
ciple which especially inheres in it. In like man-
ner, whether the auricles or the ventricles of
the heart are the chief, the auricles being the
first to live and pulsate, the last to die. Further,
whether the left ventricle, which in man is of
greater length, and is also surrounded with
thicker and more fleshy walls, and is regarded
as the source of the spirits, be hotter, more spir-
itous, excitable, and excellent, than the right,
which contains a larger quantity of blood, and
is the last to become unstrung by death; in
which the blood of the dying accumulates, con-
geals, and is deprived of life and spirit; to which,
moreover, as to a fountain head, the first um-
bilical veins bring their blood, and from which
they themselves derive their origin.
So much appears from careful observation of
the order observed in the production of the
parts, and certain other points that follow as
deductions from these, and do not a little mili-
tate against the commonly received physio-
logical doctrines, viz. : since it is manifest that
sensation and motion exist before the brain, all
sensation and motion do not proceed from the
brain; from our history it is clearly ascertained
that sense and movement inhere in the very
first drop of blood produced in the egg, before
there is a vestige of the body. The first scaffold-
ing or rudiment of the body, too, which we
have said is merely mucilaginous, before any of
the extremities are visible, and when the brain
is nothing more than a limpid fluid, if lightly
pricked, will move obscurely, will contract and
twist itself like a worm or caterpillar, so that it
is very evidently possessed of sensation.
There are yet other arguments deduced from
sense and motion whence we should infer that
the brain was not so much the first principle of
the body, in the way the medical writers main-
tain, as the heart, agreeably to Aristotle's view.
The motions and actions which physicians
style natural, because they take place involun-
tarily, and we can neither prevent nor moder-
ate, accelerate nor retard them by our will, and
they therefore do not depend on the brain, still
do not occur entirely without causing sensation,
but proclaim themselves subject to sense, inas-
much as they are aroused, called forth, and
changed thereby. When the heart, for example,
is affected with palpitation, tremor, lipothymia,
syncope, and with great variety in the extent,
rapidity, and order or rhythm of its pulsations,
we do not hesitate to ascribe these to morbific
causes implicating, deranging its sensation. For
whatever by its divers movements strives against
irritations and troubles must necessarily be en-
dowed with sensation.
The stomach and bowels, disturbed by the
presence of vitiated humours, are affected with
ructus, flatus, vomiting, and diarrhcea; and as
it lies not in our power either to provoke or to
restrain their motions, neither are we aware of
any sensation dependent on the brain which
should arouse the parts in question to motions
of the kind.
It is truly wonderful to observe the effect of
taking a solution of antimony, which we neither
distinguish by the taste, nor find any inconven-
ience from, whether in the swallowing or the
rejection. Nevertheless there is a certain dis-
criminating sense in the stomach which distin-
guishes what is hurtful from what is useful, and
by which vomiting is induced.
Nay, the flesh itself readily distinguishes a
poisoned wound from one that is not poisoned,
and on receipt of the former contracts and con-
denses itself, whereby phlegmonous tumours
are produced, as we find in connexion with the
stings of bees, gnats, and spiders.
I have myself, for experiment's sake, occa-
ANIMAL GENERATION
457
sionally pricked my hand with a clean needle,
and then having rubbed the same needle on the
teeth of a spider, I have pricked my hand in
another place. I could not by my simple sensa-
tion perceive any difference between the two
punctures; nevertheless there was a capacity in
the skin to distinguish the one from the other;
for the part pricked with the envenomed needle
immediately contracted into a tubercle, and by
and by became red, and hot, and inflamed, as if
it collected and girded itself up for a contest
with the poison for its overthrow.
The sensations which accompany affections
of the uterus, such as twisting, decubitus, pro-
lapse, ascent, suffocation, &c., and other incon-
veniences and irritations, do not depend on the
brain or on common sensation; yet neither are
these to be presumed as happening without all
consciousness. For that which is wholly with-
out sense is not seen to be irritated by any
means, neither can it be stimulated to motion
or action of any kind. Nor have we any other
means of distinguishing between an animate
and sentient thing and one that is dead and
senseless than the motion excited by some other
irritating cause or thing, which as it incessantly
follows, so does it also argue sensation.
But we shall have an opportunity of speaking
further of this matter when we discuss the ac-
tions and uses of the brain. Respect for our
predecessors and for antiquity at large inclines
us to defend their conclusions to the extent that
love of truth will allow. Nor do I think it be-
coming in us to neglect and make little of their
labours and conclusions who bore the torch
that has lighted us to the shrine of philosophy.
I am, therefore, of opinion that we should con-
clude in this way : we have consciousness in our-
selves of five principal senses, by which we
judge of external objects; but we do not feel
with the same sense by means of which we are
conscious that we feel — seeing with our eyes,
we still do not know by them that we see, but
by another sense or sensitive organ, namely,
the internal common sensation or common
sensorium, by which we examine those things
that reach us through each of the external sen-
soria, and distinguish that which is white from
that which is sweet or hard. Now this sensorium
commune to which the species or impressions
of all the external instruments of sensation are
referred, is obviously the brain, which along
with its nerves and the external organs annexed,
is held and esteemed to be the adequate instru-
ment of sensation. And this brain is like a sensi-
tive root to which a variety of fibres tend, one
of which sees, another hears, a third touches,
and a fourth and a fifth smell and taste.
But as there are some actions and motions
the government or direction of which is not
dependent on the brain, and which are there-
fore called natural, so also is it to be concluded
that there is a certain sense or form of touch
which is not referred to the common sensorium,
nor in any way communicated to the brain, so
that we do not perceive by this sense that we
feel; but, as happens to those who are deranged
in mind, or who are agitated to such a degree
by violent passion that they feel no pain, and
pay no regard to the impressions made on their
senses, so must we believe it to be with this
sense, which we therefore distinguish from the
proper animal sense. Now such a sense do we
observe in zoophytes or plant-animals, in
sponges, the sensitive plant, &c.
Wherefore, as many animals are endowed
with both sense and motion without having a
common sensorium or brain, such as earth-
worms, caterpillars of various kinds, chrysa-
lides, &c., so also do certain natural actions
take place in the embryo and even in ourselves
without the agency of the brain, and a certain
sensation takes place without consciousness.
And as medical writers teach that the natural
differ from the animal actions, so by parity of
reason does the natural sense of touch differ
from the animal sense of touch— it constitutes,
in a word, another species of touch; and whilst
the one is communicated to the common sen-
sorium, the other is not so communicated.
Further, it is one thing for a muscle to be
contracted and moved, and another for it by
regulated contractions and relaxations to per-
form any movement, such as progression or
prehension. The muscles or organs of motion,
when affected with spasms or convulsions from
an irritating cause, are assuredly moved no
otherwise than the decapitated cock or hen,
which is agitated with many convulsive move-
ments of its legs and wings, but all confused and
without a purpose, because the controlling
power of the brain has been taken away — com-
mon sensation has disappeared, under the con-
trolling influence of which these motions were
formerly coordinated to progression by walking
or to flight.
We therefore conceive the fact to be that all
the natural motions proceed from the power of
the heart, and depend on it; the spontaneous
motions, however, and those that complete any
motion which physicians entitle an animal mo-
tion, cannot be performed without the control-
WILLIAM HARVEY
ling influence of the brain and common sensa-
tion. For inasmuch as by this common sensa-
tion we are conscious of our perceptions, so also
are we conscious that we move, and this whether
the motion be regular or otherwise.
We have an excellent example of both of
these kinds of motion in respiration. For the
lungs, like the heart, are continually carried up-
wards and downwards by a natural movement,
and are excited by any irritation to coughing
and more frequent action; but they cannot
form and regulate the voice, nor can singing be
executed, without the assistance, and in some
sort the command, of the sensorium commune.
But these matters will be more fully handled
when we come to speak of the actions and uses
of the brain, and to consider the vital principle
or soul. So much we have thought fit to say by
the way, that we might show the respect in
which we hold our illustrious teachers, and our
anxiety to carry them along with us in our
labours.
EXERCISE 58. Of the nutrition of the chicly IN ovo
That the authority of the ancients is not to
be rashly thrown off appears in this: it was for-
merly current doctrine, though many at the
present day, Fabricius1 among the number, re-
ject it as a delusion and a foolish idea, that the
embryo sucked in its mother's womb. This idea
nevertheless had Democritus, Epicurus, and
Hippocrates for its supporters; and the father
of physic contends for it on two principal
grounds: "Unless the foetus sucked," he says,2
"how should excrements be formed? or how
should it know how to suck immediately after
it is born?"
Now, whilst in other instances it is customary
to swear by the bare statement of this ancient
and most distinguished writer, his ipse dixit
(dur6$ ^ty) sufficing, because he here makes
an assertion contrary to the commonly received
opinion, Fabricius not only denies the state-
ment, but spurns the arguments in support of
his conclusion. We, however, leave it to the
judgment of skilful anatomists and learned
physicians to say whether our observations on
the generation of animals do not proclaim this
opinion of Hippocrates to be not merely prob-
able, but even necessary.
All admit that the foetus in utero swims in the
midst of an abundance of a watery fluid, which
in our history of the egg we have spoken of as
the colliquament, this fluid modern authorities
1 Dcform.foftUt pp. 19 and 134.
1 DC earn, ct de not.
regard as the sweat and excrement of the foetus,
and ascribe as its principal use the protection of
the uterus against injury from the foetus during
any violent motion of the mother in running or
leaping; and, on the other hand, the defence of
the foetus from injury through contact with
neighbouring bones, or an external cause, par-
ticularly during the period when its limbs are
still delicate and weak.
Fabricius ascribes additional uses to this fluid,
viz., "that it may moisten and lubricate all the
parts around, and dispose the neck of the uterus
to facile and speedy dilatation to the utmost
extent; and all this is not less assisted by that
thick, white, excrementitious matter of the
third digestion, neglected by the ancients, which
is unctuous and oily, and further prevents the
sweat, which may occasionally be secreted sharp
and salt in quality, from excoriating the tender
body of the foetus."3
I readily acknowledge all the uses indicated,
viz., that the tender foetus may be secure against
all sudden and violent movements of the mother,
that he may ride safe in the "bat's wings," as
they are called, and, surrounded with an abun-
dance of water, that he may escape coming into
contact with his mother's sides, being restrained
by the retinacular fluid on either hand: this
circumambient fluid must certainly protect the
body which floats in its middle from all external
injury. But, as in many other instances, my
observations compel me here to be of a different
opinion from Fabricius. In the first place, I am
by no means satisfied that this fluid is the sweat
of the foetus. And then I do not believe that the
fluid serves those important purposes in parturi-
tion which he indicates; and much less that it is
ever so sharp and saline that an unctuous cover-
ing was requisite to protect the foetus from its
erosive effects, particularly in those cases where
there is already a thick covering of wool, or
hair, or feathers. The fluid, in fact, has a pleas-
ant taste, like that of watery milk, so that al-
most all viviparous animals lap it up, and cleanse
their new-born progeny by licking them with
their tongues, greedily swallowing the fluid,
though none of them was ever seen to touch
any of the excrements of their young.
Fabricius spoke of this fluid as saline and
acrimonious, because he believed it to be sweat.
But what inconvenience, I beseech you, were
sweat to the chick, already covered with its
feathers? — if indeed anyone ever saw a chicken
sweat. Nor do I think he could have said that
the use of this fluid in the egg was, by its mois-
• Of. «/., p. 137.
ANIMAL GENERATION
459
tening and lubrifying qualities, to facilitate the
birth of the chick; for the drier and older the
shell of the egg, the more friable and fragile it
becomes. Finally, were it the sweat of the em-
bryo, or foetus, it ought to be most abundant
nearest the period of parturition: the larger the
foetus and the more food it consumes, the more
sweat must it necessarily secrete. But shortly
before the exclusion of the chick from the egg,
namely, about the nineteenth or twentieth day,
there is none of the fluid to be seen, because as
the chick grows it is gradually taken up; so that
if the thing be rightly viewed, the fluid in ques-
tion ought rather to be regarded as nutriment
than as excrement, particularly as he has said
that the chick in the egg breathes, and lets its
chirping be heard, which it certainly would not
do were it surrounded with water.
But all experienced obstetricians know that
the watery fluid of the secundines is of no great
use either in lubricating the parts or in facili-
tating the progress of parturition in the way
Fabricius would have it. For the parts sur-
rounding the vulva are relaxed of themselves,
and by a kind of proper maturity at the full
time, without any assistance from the uterine
waters; and particularly those that offer the
greatest obstacles to the advance of the foetus,
namely, the ossa pubis and the os coccygis, to
which the attention of the midwife is especially
directed in assisting the woman in labour. For
midwives are much less studious to anoint the
soft parts with any emollient salves, lest they
tear, than careful to pull the os coccygis out-
wards, a business in which, if the fingers do not
suffice, they have recourse to the uterine specu-
lum, applied by the hand of the experienced
surgeon, an instrument having three sides or
branches, one of which bearing on the os coccy-
gis, the other two on the ossa pubis, the busi-
ness of distension is effected by force. For the
head of the child that is about to be born, when
it makes the turn, and is forced downwards, re-
laxes and opens the os uteri; but coming down
he will stick fast, and scarcely be brought forth
if he chance to abut upon the point of the os
coccygis, and immediately the case is one not
without danger both to the child and mother.
But nature's intention was obviously to relax
and soften all the parts concerned; and the at-
tendant knows that when the uterine orifice is
discovered in a soft and lax condition, by the
finger introduced, it is an infallible sign that
the delivery is at hand even though the waters
have not broken. Indeed—and I do not speak
without experience — if anything remains in the
uterus for expulsion, either after delivery or at
any other time, and the uterus makes efforts to
get rid of it, the orifice both descends lower and
is found soft and relaxed. If the uterine orifice
recedes, and is found somewhat hard after de-
livery, it is a sign of the woman's restoration to
health.
Taught by like experience, I assert that the
ossa pubis frequently become loosened during
labour, their cartilaginous connexion being
softened, and the whole hypogastric region en-
larged in the most miraculous manner, not,
however, by any pouring out of watery fluids,
but spontaneously, as ripe fruit gapes that the
included seed may find an exit. The degree in
which the coccyx may impede delivery, how-
ever, is apparent among quadrupeds having
tails, which can neither bring forth, nor even
discharge the excrement from their bowels, un-
less the tail be raised; if you but depress the tail
with your hand, you prevent the exit of the
dung.
Moreover, the most natural labour of all is
held to be that in which the foetus and after-
birth, the waters inclusive, or the ovum, is ex-
pelled entire. Now if the membranes have not
given way, and the waters have not escaped, it
comes to pass that the surrounding parts are
more than usually distended and dilated by the
labour pains, in consequence, to wit, of the en-
tire and tense state of the membranes, by which
it happens that the foetus is produced more
speedily, and with a less amount of effort, al-
though with more suffering to the mother. In
cases of this kind we have known women who
were suffering much in their travail in conse-
quence of the too great distension, immensely
relieved by the rupture of the membranes and
the sudden escape of the waters, the laceration
being effected either with the nails of the mid-
wife or the use of a pair of forceps.
Experienced midwives are further aware that
if the waters come away before the orifice of
the uterus is duly dilated, the woman is apt to
have a lingering time and a more difficult de-
livery, contrary to Fabricius's notion of the
waters having such paramount influence in
softening and lubricating the parts.
Moreover, that the fluid which we have called
colliquament is not the sweat of the foetus is
made obvious, both from the history of the egg
and of the uterogestation of other animals: it is
present before the foetus is formed in any way,
before there is a trace of it to be seen; and whilst
it is still extremely small and entirely gelatinous,
the quantity of water present is very great, so
46o
WILLIAM HARVEY
that it seems plainly impossible that so small a
body should produce such a mass of excremen-
titious fluid.
It happens besides that the ramifications of
the umbilical veins are distributed over and
terminate upon the membrane which incloses
this fluid, precisely as on the membranes of the
albumen and yelk of the egg, a circumstance
from which, and the thing being viewed as it is
in fact, it appears to be clearly proclaimed that
this fluid is rather to be regarded as food than
as excrement.
To me, therefore, the opinion of Hippocrates
appears more probable than that of Fabricius
and other anatomists, who look on this liquid
as sweat, and believe that it must prove detri-
mental to the foetus. I am disposed, I say, to be-
lieve that the fluid with which the foetus is sur-
rounded may serve it for nourishment; that the
thinner and purer portions of it, taken up by
the umbilical veins, may serve for the constitu-
tion and increase of the first formed parts of the
embryo; and that from the remainder or the
milk, taken into the mouth by suction, passed
on to the stomach by the act of deglutition, and
there digested or chylified, and finally absorbed
by the mesenteric veins, the new being con-
tinues to grow and be nourished. I am the more
disposed to take this view from certain not im-
pertinent arguments, which I shall proceed to
state.
As soon as the embryo acquires a certain de-
gree of perfection it moves its extremities, and
begins to prove the actions of the organs des-
tined to locomotion. Now I have seen the chick
in ovo, surrounded with liquid, opening its
mouth, and any fluid that thus gained access to
the fauces must needs have been swallowed; for
it is certain that whatever passes the root of the
tongue and gains the top of the oesophagus,
cannot be rejected by any animal with a less
effort than that of vomiting. This fact is acted
upon every day by veterinary practitioners,
who in administering medicated drinks and
pills or boluses to cattle, seize the tongue, and
having put the article upon its root beyond the
protuberant part, the animal cannot do other-
wise than swallow it. And if we make the ex-
periment ourselves, we find that a pill carried
between the finger and thumb as far as the root
of the tongue and there dropped, immediately
the action of deglutition is excited, and unless
vomiting be produced the pill is taken down.
If the embryo swimming in the fluid in ques-
tion, then, do but open his mouth, it is abso-
lutely necessary that the fluid must reach the
fauces; and if the creature then move other
muscles, wherefore should we not believe that
he also uses his throat in its appropriate office
and swallows the fluid ?
It is further quite certain that in the crop of
the chick — and the same thing occurs in refer-
ence to the stomach of other embryos — there is
a certain matter having a colour, taste, and con-
sistence, very similar to that of the liquid men-
tioned, and some of it in the stomach digested
to a certain extent, like coagulated milk; and
further, whilst we discover a kind of chyle in
the upper intestines, we find the lower bowels
full of stercoraceous excrements. In like man-
ner we perceive the large intestines of the foe-
tuses of viviparous animals to contain excre-
ments of the same description as those that dis-
tend them when they feed on milk. In the
sheep and other bisulcated animals we even
find scybala.
Towards the seventeenth day we find dung
very obviously near the anus of the chick; and
shortly before the extrusion I have seen the
same matter expelled and contained within the
membranes. Volcher Goiter, a careful and ex-
perienced dissector, states that he has observed
the same thing.
Wherefore should we doubt, then, that the
foetus in utero sucks, and that chylopoiesis goes
on in its stomach, when we find present both
the principles and the recrementitious products
of digestion ?
And then, when we find the bladder both of
the bile and the urine full of those excrements
of the second digestion, wherefore should we
not conclude that the first digestion, or chylo-
poiesis, has preceded ?
The embryo, therefore, seeks for and sucks
in nourishment by the mouth; and you will
readily believe that he does so if you rip him
from his mother's womb and instantly put a
finger in his mouth; which Hippocrates thinks
he would not seize had he not previously sucked
whilst in the womb. For we are accustomed to
see young infants trying various motions, mak-
ing experiments, as it were, approaching every-
thing, moving their limbs, attempting to walk,
and uttering sounds, acts all of which when
taught by repeated experience, they afterwards
come to execute with readiness and precision.
But the foetus so soon as it is born, aye, before
it is born, will suck; doubtless as it had done in
the uterus long before. For I have found by ex-
perience that the child delayed in the birth,
and before it has cried or breathed, will seize
and suck a finger put into its mouth. A new-
ANIMAL GENERATION
461
born infant, indeed, is more expert at sucking
than an adult, or than he is himself if he have
but lost the habit for a few days. For the infant
does not suck by squeezing the nipple with his
lips as we should, and by suction in the com-
mon acceptation; he rather seems as if he would
swallow the nipple, drawing it wholly into his
throat, and with the aid of his tongue and pal-
ate, and chewing, as it were, he milks his mother
with more art and dexterity than an adult
could practise. He therefore appears to have
learned that by long custom, and before he saw
the light, which we know full well he unlearns
by a very brief discontinuance.
These and other observations of the same
kind make it extremely probable that the chick
in ovo is nourished in a twofold manner, namely,
by the umbilical and by the mesenteric veins.
By the former he imbibes a nourishment that
is well nigh perfectly prepared, whence the
first-formed parts are engendered and aug-
mented; by the latter he receives chyle for the
structure and growth of the other remaining
parts.
But the reason is perhaps obscure why the
same agent should perform the work of nutri-
tion by means of the same matter in a variety
of ways, since nature does nothing in vain. We
shall therefore endeavour to explain this.
What is taken up by the umbilical veins is
the purer and more limpid part; and the rest of
the colliquament in which the foetus swims is
like crude milk, or milk deprived of its purer
portion. The purer part does not require any
of that ulterior concoction of which the re-
mainder stands in need ; and to undergo which
it is taken into the stomach, where it is trans-
muted into chyle. Similar to this is the crude
and watery milk which is found in the breasts
immediately after parturition. The liquefied
albumen of the egg, and the crude or watery
milk of the mammae seem to have in all respects
the same colour, taste, and consistence. For the
first flow of milk is serous and watery, and
women are wont to express water from their
breasts before the milk comes white, concocted,
and perfect. »,
Just as the colliquament found in the crop of
the chick is a kind of crude milk, whilst the
same fluid discovered in the stomach is con-
cocted, white, and curdled; so in viviparous
animals, before the milk is concocted in the
mammae, a kind of dew and colliquament makes
its appearance there, and the colliquament only
puts on the semblance of milk after it has un-
dergone concoction in the stomach. And so it
happens, in Aristotle's opinion, that the first
and most essential parts are formed out of the
purer and thinner portion of the colliquament,
and are increased by the remaining more indif-
ferent portion after it has undergone elabora-
tion by a new digestion in the stomach. In the
same way are the other less important parts de-
veloped and maintained. Thus has nature, like
a fond and indulgent mother, been sedulous
rather to provide superfluity, than to suffer any
scarcity of things necessary. Or it might be said
to be in conformity with reason to suppose that
the foetus, now grown more perfect, should also
be nourished in a more perfect manner, by the
mouth, to wit, and by a more perfect kind of
aliment, rendered purer by having undergone
the two antecedent digestions and been thereby
freed from the two kinds of excrementitious
matter. In the beginning and early stages, nour-
ished by the ramifications of the umbilical
veins, it leads in some sort the life of a plant;
the body is then crude, white, and imperfect;
like plants, too, it is motionless and impassive.
As soon, however, as it begins by the mouth to
partake of the same aliment further elaborated,
as if feeling a diviner influence, boasting a higher
grade of vegetative existence, the gelatinous
mass of the body is changed into flesh, the or-
gans of motion are distinguished, the spirits are
perfected, and motion begins; nor is it any
longer nourished like a vegetable, by the roots,
but, living the life of an animal, it is supported
by the mouth.
EXERCISE 59. Of the uses of the entire egg
Having now gone through the several changes
and processes which must take place in the
hen's egg, in order that it may produce a chick,
Fabricius proceeds to consider the uses of the
egg at large, and of its various parts; nor does
he restrict himself to the hen's egg, but con-
descends upon eggs in general. Among other
things he inquires: wherefore some eggs are
heterogeneous and composed of different ele-
ments; and others are homogeneous and simi-
lar? such as the eggs of insects, and those crea-
tures that are engendered from the whole egg,
viz., by metamorphosis, and are not engen-
dered from one part of the egg, and nourished
by another part.
I have no purpose myself of entering on a
general consideration of eggs of all kinds and
descriptions; I have not yet given the history
of all, but only of the hen's egg; so that I shall
here limit myself to a survey of the uses of the
common hen's egg, keeping in view the end of
462
WILLIAM HARVEY
all its actions, which is nothing less than the
production and completion of a new being, as
Fabricius has well and truly said.1
Among the points having reference to the
whole egg, Fabricius speaks of the form, dimen-
sions, and number of eggs. "The figure of the
egg is round," he says,2 "in order that the mass
of the chick may be stowed in the smallest pos-
sible space; for the same cause that God made
the world round, namely, that it might em-
brace all things; and it is from this, as Galen
conceives, that this figure is always felt to be
most agreeable and consonant to nature. Fur-
ther, as it has no angles exposed to injury from
without, it is, therefore, the safest figure, and
the one best adapted to effect the exclusion of
the chick.*' It had been well after such a preface
to have assigned satisfactory causes why hen's
eggs are not spherical, like the eggs of fishes,
worms and frogs, but oblong and pointed; to
have shown what there is in them which hin-
ders the presumed perfection of figure. Now to
me the form of the egg has never appeared to
have aught to do with the engenderment of the
chick, but to be a mere accident; and to this
conclusion I come the rather when I see such
diversities in the shape of the eggs of different
hens. They vary, in short, in conformity with
the variety that obtains among the uteri of dif-
ferent fowls, in which, as in moulds, they re-
ceive their form.
Aristotle,8 indeed, says that the longer-shaped
eggs produce females, the rounder males. I have
not made any experiments upon this point my-
self. But Pliny4 asserts, in opposition to Aris-
totle, that the rounder eggs produce females,
the others males. Now were there any certainty
in such statements, either in one way or the
other, some hens would always produce males,
others always females, inasmuch as the eggs of
the same hen are in many instances always of
one figure, namely, either much rounded or
acutely pointed. Horace5 thought that the ob-
long eggs, as being the more perfect and better
concocted, and therefore the better flavoured,
produced males.
I willingly pass by the reasons alleged by
Fabricius for the form of eggs, as being all
irrelevant.
The size of an egg appears to bear a propor-
tion to the size of the foetus produced from it;
1 Loc. «/., p. 50.
* DC usu pan.> x.
8 History of 'Animals, vi. 2.
4 Hist, nat.^ x. 52.
• Pliny, ibid.
large hens, too, certainly lay large eggs. The
crocodile, however, lays eggs the size of those
of the goose; nor does any animal attain to
larger dimensions from a smaller beginning. It
would seem, too, that the size of the egg and
the quantity of matter it contained had some
connexion with its fecundity, inasmuch as the
very small eggs called centenines are all barren.
The number of eggs serves the same end as
abundance of conceptions among viviparous
animals — they secure the perpetuity of the spe-
cies. Nature appears to have been particularly
careful in providing a numerous offspring to
those animals which, by reason of their pusillan-
imity or bodily weakness, hardly defend them-
selves against the attacks of others; she has
counterbalanced the shortness of their own
lives by the number of their progeny. "Na-
ture," says Pliny,6 "has made the timid tribes
among birds more fruitful than the bold ones."
All generation, as it is instituted by nature for
the sake of perpetuating species, so does it occur
more frequently among those that are shorter-
lived and more obnoxious to external injury
lest their race should fail. Birds that are of
stronger make, that prey upon other creatures,
and therefore live more securely and for longer
terms scarcely lay more than two eggs once a
year. Pigeons, turtle and ring-doves, that lay
but a couple of eggs, make up for the smallness
of the number by the frequency of laying, for
they will produce young as often as ten times
in the course of a year. They, therefore, engen-
der greatly although they do not produce many
at a time.
EXERCISE 60. Of the uses oftheyel^and albumen
"An egg," says Fabricius,7 "properly so called,
is composed of many parts, because it is the or-
gan of the engenderer, and Galen everywhere
insists on the constitution of an organ as imply-
ing multiplicity of parts." But this view leads
us to ask whether every egg must not be hetero-
geneous, seeing that every egg is organic ? And
every egg, indeed, even that of the fish and in-
sect, appears to be composed of several different
parts— membranes, coverings, defences; nor is
the included matter by any means without di-
versity of constitution in different parts.
Fabricius agrees further, and correctly, with
Galen, when he says: "Some parts of the egg
are the chief instruments of the actions that
take place in it, others may be styled necessary
—without them no actions could take place;
Op. sup. cit., p. 47.
ANIMAL GENERATION
463
others exist that the action which takes place
may be better performed; others, in fine, are
destined for the safety and preservation of all
of these."1 But he is mistaken when he says: "If
we speak of the prime action, which is the gen-
eration of the chick, the chief cause of this is the
semen and the chalazae, these two being the
prime cause of the generation of the chick, the
semen being the efficient cause, the chalaza the
matter only." Now according to the opinion of
Aristotle, it must be allowed that that which
generates is included in the egg; but Fabricius
denies that the semen of the cock is contained
in the egg.
Nor does he wander less wide of the mark
when he speaks of the chalazae as the matter
from which, by the influence of the semen galli,
the chick is incorporated. For the chick is not
£ reduced either from one or the other, nor yet
:om both of the chalazae, as we have shown in
our history. Neither is the generation of the
chick effected by metamorphosis, nor by any
new form assumed and division effected in the
chalazae, but by epigenesis, in the manner al-
ready explained. Nor are the chalazae especially
fecundated by the semen of the male bird, but
the cicatricula rather, or the part which we
have called the eye of the egg, from which,
when it enlarges, the colliquament is produced,
in and from which, subsequently, the blood,
the veins, and the pulsating vesicles proceed,
after which the whole body is gradually formed.
Moreover, on his own admission, the semen of
the cock never enters the uterus of the hen, and
yet it fecundates not only the eggs that are al-
ready formed, but others that are yet to be
produced.
Fabricius refers the albumen and vitellus to
the second action of the egg, which is the nutri-
tion and growth of the chick. "The vitellus and
albumen," he says,2 "are in quantity commen-
surate with the perfect performance of this ac-
tion, and with the due Development and growth
of the chick. The sliell and membranes are,
therefore, the safety of the whole of the egg as
well as the security of its action. But the veins
and arteries which carry nourishment are organs
without which the action of the egg, in other
words, the growth and nutrition of the chick,
would not take place." It is uncertain, how-
ever, whether the umbilical vessels of the em-
bryo or the veins and arteries of the mother,
whence the egg is increased, are here to be un-
derstood. For a like reason the uterus, and in-
1 Ibid., p. 48.
tf., p. 48.
cubation ought to be referred to this last class
of actions.
We have to do, then, with the two fluids of
the egg, the albumen and the vitellus; for these,
before all the other parts, are formed for the
use of the embryo, and in them is the second
action of the egg especially conspicuous.
The egg of the common hen is of two colours
internally, and consists of two fluids, severally
distinct, separated by membranes, and in all
probability of different natures, and therefore
having different ends to serve, inasmuch as they
are distinguished by different extensions of the
umbilical veins, one of them proceeding to the
white, another to the yelk. "The yelk and white
of the egg are of opposite natures," says Aris-
tptle,3 "not only in colour, but also in power.
For the yelk is congealed by cold; the white is
not congealed, but is rather liquefied; on the
contrary, the white is coagulated by heat, the
yelk is not coagulated, but remains soft, unless
it be overdone, and is more condensed and
dried by boiling than by roasting." The vitellus
getting heated during incubation, is rendered
more moist; for it becomes like melted wax or
tallow, whereby it also takes up more room.
For as the embryo grows, the albumen is gradu-
ally taken up and becomes inspissated; but the
yelk, even when the foetus has attained perfec-
tion; appears scarcely to have diminished in
size; it is only more diffluent and moist, even
when the foetus begins to have its abdomen
closed in.
Aristotle gives the following reason for the
diversity: "Since the bird cannot perfect her
offspring within herself, she produces it along
with the aliment needful to its growth in the
egg. Viviparous animals again prepare the food
(milk) in another part of their body, namely,
the breasts. Now nature has done the same
thing in the egg; but otherwise than as is gen-
erally presumed, and as Alcmaeon Crotoniates
states it, for it is not the albumen but the vitellus
which is the milk of the egg."4
For as the foetus of a viviparous animal draws
its nourishment from the uterus whilst it is con-
nected with its mother, like a plant by its roots
from the earth; but after birth, and when it has
escaped from the womb, sucks milk from the
breast, and thereby continues to wax in size
and strength, the chick finds the analogue of
both kinds of food in the egg. So that whilst in
viviparous animals the uterus exists within the
parent, in oviparous the parent may rather be
* History of Animals, vn. 2,
4 On the Generation of Animals, ra. 2.
464
WILLIAM HARVEY
said to exist within the uterus (the egg). For
the egg is a kind of exposed and detached uter-
us, and in it are included in some sort vicarious
mammae. The chick in the egg, I say, is first
nourished by albumen, but afterwards, when
this is consumed, by the yelk or by milk. The
umbilical vascular connexion with the albu-
men, therefore, when this fluid is used up, with-
ers and is interrupted when the abdomen comes
to be closed, and before the period of exclusion
arrives, so that it leaves no trace of its existence
behind it: in viviparous animals, on the con-
trary, the umbilical cord is permanent in all its
parts up to the moment of birth. The other
canal that extends to the vitellus, however, is
taken up along with this matter into the abdo-
men, where being stored, it serves for the sup-
port of the delicate foetus until its beak has ac-
quired firmness enough to seize and bruise its
food, and its stomach strength sufficient to
comminute and digest it; just as the young of
the viviparous animal lives upon milk from the
mammae of its mother, until it is provided with
teeth by which it can masticate harder food.
For the vitellus is as milk to the chick, as has
been already said; and the bird's egg, as it stands
in lieu both of uterus and mammae, is furnished
with two fluids of different colours, the white
and the yelk.
All admit this distinction of fluids. But I, as I
have already said, distinguish two albumens in
the egg, kept separate by an interposed mem-
brane, the more external of which embraces the
other within it, in the same way as the yelk is
surrounded by the albumen in general. I have
also insisted on the diverse nature of these albu-
mens; distinguished both by situation and their
surrounding membranes, they seem in like man-
ner calculated for different uses. Both, how-
ever, are there for ends of nutrition, the outer-
most, as that to which the branches of the um-
bilical veins are earliest distributed, being first
consumed, and then the inner and thicker por-
tion; last of all the vitellus is attacked, and by
it is the chick nourished, not only till it escapes
from the shell but for some time afterwards.
But upon this point we shall have more to
say below, when we come to speak of the man-
ner in which the foetuses of viviparous animals
are developed, and at the same time demon-
strate that these all derive their origin from
eggs, and live by a twofold albuminous food in
the womb. One of these is thinner, and con-
tained within the ovum or conception; the
other is obtained by the umbilical vessels from
the placenta and uterine cotyledons. The fluid
of the ovum resembles a dilute albumen in col-
our and consistence; it is a sluggish, pellucid
liquid, in all respects similar to that which we
have called the colliquament of the egg, in
which the embryo swims, and on which it feeds
by the mouth. The fluid which the foetus obtains
from the uterine placenta by the aid of the um-
bilical vessels is more dense and mucaginous,
like the inspissated albumen. Whence it clearly
appears that the foetus in utero is no more nour-
ished by its parent's blood than is the suckling
afterwards, or the chick in ovo; but that it is
nourished by an albuminous matter concocted
in the placenta, and not unlike white of egg.
Nor is the contemplation of the Divine Prov-
idence less useful than delightful when we see
Nature, in her work of evolving the foetus, fur-
nishing it with sustenance adapted to its vary-
ing ages and powers, now more easy, by and by
more difficult of digestion. For as the foetus ac-
quires greater powers of digesting, so is it sup-
plied with food that is successively thicker and
harder. And the same thing may be observed in
the milk of animals generally: when the young
creature first sees the light the milk is thinner
and more easy of concoction; but in the course
of time, and with increased strength in the
suckling, it becomes thicker, and is more abun-
dantly stored with caseous matter. Those flabby
and delicate women, therefore, who do not
nurse their own children, but give them up to
the breast of another, consult their health in-
differently; for mercenary nurses being for the
major part of more robust and hardy frames,
and their milk consequently thicker, more
caseous, and difficult of digestion, it frequently
happens that milk of this kind given to the in-
fants of such parents, particularly during the
time of teething, is not well borne, but gives
rise to crudities and diarrhoeas, to griping, vom-
iting, fever, epilepsy, and other formidable dis-
eases of the like nature.
What Fabricius says,1 and strives to bolster
up by certain reasonings, of the chalazae stand-
ing for the matter of the chick, we have already
thrown out in our history, and at the same time
have made it manifest that the substance of the
chick and its first rudiments were produced
whilst the chalazae were still entire and un-
changed, and in a totally different situation.
Neither is it true, as he states, "that the
chalazae, rendered fruitful by the semen of the
cock, stand in the place of seed, and that from
them the chick is produced."2 Nor are the cha-
1 Op. «/., p. 34.
ANIMAL GENERATION
465
lazae, as he will have it, "in colour, substance,
and bodily properties so like seed, or bear so
strong a resemblance to the embryo in a boiled
egg, that we may rightly conceive all the parts
designated spermatic to be thence engendered."1
I am rather of opinion that the fluid which we
have called colliquament, or the thinner por-
tion of the albumen liquefied and concocted, is
to be regarded as of the nature of seed, and, if
the testimony of our eyes is to be credited, as a
substitute for it.
The observation of this venerable old man is
therefore unnecessary when he says, "As the
whole animal body is made up of two substances
very different from one another, and even of
opposite natures, viz., hot and cold— among the
hot parts being included all those that are full
of blood and of a red colour; among the cold all
those that are exsanguine and white — these two
orders of parts doubtless require a different and
yet a like nourishment, if it be true that we are
nourished by the same things of which we are
made. The spermatic, white, and cold parts,
therefore, require white and cold nourishment;
the sanguineous, red, and hot parts, again, de-
mand nourishment that is red and hot. And so
is the cold white of the egg properly held to
nourish the cold and white parts of the chick,
and the hot and sanguine yelk regarded as a
substitute for the hot and purple blood. In this
way do all the animal parts obtain nourishment
suitable and convenient for them."2 Now we
by no means admit that the two fluids or mat-
ters of the egg are there as appropriate means
of nourishment for different orders of parts.
For we have already said that the heart, lungs,
kidneys, liver, spleen, muscles, bones, liga-
ments, &c., &c., were all alike and indiscrimi-
nately white and bloodless on their first for-
mation.
Further, on the preceding view of Fabricius
it would follow that the heart, lungs, liver,
spleen, &c., were not spermatic parts, did not
originate from the seed (which he, however,
will by no means allow), inasmuch as they too
are by and by nourished by the blood and grow
out of it; for every part is both formed and
nourished by the same means, and nutrition is
nothing more than the substitution of a like
matter in the room of that which is lost.
Nor would he find less difficulty in answering
the question: how it happens that when the
albumen in the egg is all consumed, the cold
and white parts, such as the bones, ligaments,
p. 57.
p. 55-
brain, spinal marrow, &c., continue to be nour-
ished and to grow by means of the vitellus?
which to these must be nourishment as inap-
propriate as albumen to the hot, red, and san-
guine parts.
Adopting the views commented on, indeed,
we should be compelled to admit that the hot
and sanguineous parts were the last to be pro-
duced: the flesh after the bones; the liver,
spleen, and lungs after the ligaments and intes-
tinal canal; and further, that the cold parts of
the chick must come together and attain ma-
turity, the white being all the while consumed,
and the hot parts be engendered subsequently,
when the vitellus fails and ceases from nourish-
ing them; and then it would be certain that all
the parts could not take their rise in and be con-
stituted out of the same clear liquid. All such
conclusions, however, are refuted by simple
ocular inspection.
I add another argument to those already sup-
plied: the eggs of cartilaginous fishes — skates,
the dog-fish, &c.-— are of two colours; their
yelks are of a good deep colour; nevertheless,
all the parts of these fishes are white, bloodless,
and cold, not even excepting the substance of
their liver. On the contrary, I have seen a cer-
tain breed of fowls of large size, their feathers
Iblack, their flesh well supplied with blood, their
iver red; yet were the yelks of the eggs of these
fowls — fruitful eggs — of the palest shade of
yellow, not deeper than the tint of ripe barley
straw.
Fabricius, however, seems in these words to
retract all he has but just said: "There is one
thing to be particularly wondered at both in
the yelk and the white, viz., that neither of
them being blood, they are still so near to the
nature of blood that they in fact differ but very
slightly from it — there is but little wanting to
constitute either of them blood; so that little
labour and a very slight concoction suffice to
effect the change. The veins and arteries dis-
tributed to the membranes of both the white
and yelk are consequently seen replete with
blood at all times; the white and yelk neverthe-
less continuing possessed of their own proper
nature, though either, so soon as it is imbibed
by the vessels, is changed into blood, so closely
do they approach in constitution to this fluid/'3
But if it be matter of certainty that blood
exists no less in the vessels distributed to the
albumen than in those sent to the vitellus, and
that both of these fluids are so closely allied to
blood in their nature, and turn into blood so
• Op. tit., p. 55.
466
WILLIAM HARVEY
readily; who, I beseech you, will doubt that the
blood, and all the parts which are styled san-
guineous, are nourished and increased through
the albumen as well as the vitellus?
Our author, however, soon contrives a sub-
terfuge from this conclusion: "Although all this
be true," he says,1 "still must we conceive that
the matter which is imbibed by the veins from
the yelk and white is only blood in the same
sense as the chyle in the mesenteric veins, in
which nothing but blood is ever seen; now chyle
is but the shadow of blood, and is first perfected
in the liver; and in like manner the matter
taken up by the veins from the white and yellow
is only the shadow of blood," &c. Be it so; but
hiding under this shadow, he does not answer
the question, wherefore the blood and blood-
like parts should not, for the reasons cited, be
equally well nourished by the albumen as by
the vitellus?
Had our author, in like manner, asserted that
the hotter parts are rather nourished by that
blood which is derived from the vitellus than
by that attracted from the albumen, and the
colder parts, on the other hand, by that which
is derived from the albumen, I should not my-
self have been much disposed to gainsay him.
There is one consideration in the whole ques-
tion, however, which is sorely against him; it is
this — how is the blood formed in the egg? by
what agent is either white or yelk turned into
blood whilst the liver is not yet in existence?
For in the egg, at all events, he could not say
that the blood was transfused from the mother.
He says, indeed, "This blood is produced and
concocted in the veins rather than in the liver;
but it becomes bone, cartilage, flesh, &c. in the
parts themselves, where it undergoes exact con-
coction and assimilation." In this he adds noth-
ing; he neither tells us how or by what means
perfect blood is concocted and elaborated in
the minute veins both of the albumen and vitel-
lus, the liver, as I have said, not having yet
come into existence—not a particle of any part
of the body, in fact, having yet been produced
by which either concoction or elaboration might
be effected. And then, forgetful of what he has
previously said, viz., that the hot and haematous
parts are nourished by the vitellus and the cold
and anaemic parts by the albumen, he is plainly
in contradiction with himself when he admits
that the same blood is turned into bone, carti-
lage, flesh, and all other parts.
More than this, Fabricius has slipped the
greatest difficulty of all, the source of not a
little doubt and debate to the medical mind,
viz., how the liver should be the source and
artificer of the blood, seeing that this fluid not
only exists in the egg before any viscus is formed,
but that all medical writers teach that the pa-
renchymata of the viscera are but effusions of
blood ? Is the work the author of its workman ?
If the parenchyma of the liver come from the
blood, how can it be the cause of the blood ?
What follows is of the same likelihood : "There
is another reason wherefore the albumen should
be separated from the yelk, namely, that the
foetus may swim in it, and be thus supported,
lest tending downwards by its own weight, it
should incline to one particular part, and drag-
ging, should break the vessels, in preventing
which the viscidity and purity of the albumen
contribute effectually. For did the foetus grow
amid the yelk, it might readily sink to the bot-
tom, and so cause laceration of that body." Suf-
ficiently jejune! For what, I entreat, can the
purity of the albumen contribute to the sup-
port of the embryo ? Or how should the thinner
albumen sustain it better than the thicker and
more earthy yelk? Or where the danger, I ask,
of its sinking down, when we see that the egg
in incubation is always laid on its side, and there
is nothing to fear either for the ascent or the
descent of the embryo? It is indubitable, in-
deed, that not only does the embryo of the
chick float in the egg, but that the embryo of
every animal during its formation floats in the
uterus; this however takes place amidst the
fluid which we have called colliquament, and
neither in the albumen nor vitellus, and we
have elsewhere given the reason wherefore
this is so.
"Aristotle informs us," says Fabricius, "that
the vitellus rises to the blunt end of the egg
when the chick is conceived; and this because
the animal is incorporated from the chalaza,
which adheres to the vitellus; whence the vitel-
lus which was in the middle is drawn towards
the upper wider part of the egg, that the chick
may be produced where the natural cavity ex-
ists, which is so indispensable to its well-being."
The chalaza, however, is certainly connected
still more intimately with the albumen than
with the yelk.
My mode of interpreting the ascent in ques-
tion is this: the spot or cicatricula conspicuous
on the membrana vitelli, expands under the in-
fluence of the spirituous colliquament engen-
dered within it, and requiring a larger space, it
tends towards the blunt end of the egg. The
liquefied portion of the vitellus and albumen,
ANIMAL GENERATION
467
diluted in like manner, and concocted and made
more spirituous, swims above the remaining
crude parts, just as the inferior particles of water
in a vessel, when heated, rise from the bottom
to the top, a fact which every medical man
must have observed when he had chanced to
put a measure of thick and turbid urine into a
bath of boiling water, in which case the upper
part first becomes clear and transparent. An-
other example will make this matter still more
plain. There is an instrument familiar to almost
everybody, made rather for amusement than
any useful purpose, nearly full of water, on the
surface of which float a number of hollow glass
beads which by their lightness and swimming
together support a variety of figures, Cupids
with bows and quivers, chariots of the sun,
centaurs armed, and the like, which would else
all sink to the bottom. So also does the eye of
the egg, as I have called it, or first colliquament,
dilated by the heat of the incubating fowl and
genital virtue inherent in the egg, expand, and
thereby rendered lighter, rise to the top, when
the vitellus, with which it is connected follows.
It is because the cicatricula, formerly situated
on the side of the vitellus, now tends to rise di-
rectly upwards that the thicker albumen is
made to give place, and the chalazae are carried
to the sides of the egg.
EXERCISE 61. Of the uses of the other farts
of the egg
The shell is hard and thick that it may serve
as a defence against external injury to the fluids
and the chick it includes. It is brittle, neverthe-
less, particularly towards the blunt end, and as
the time of the chick's exclusion draws near,
doubtless that the birth may suffer no delay.
The shell is porous also; for when an egg, partic-
ularly a very recent one, is dressed before the
fire, it sweats through its pores. Now these pores
are useful for ventilation; they permit the heat
of the incubating hen to penetrate more readily,
and the chick to have supplies of fresh air; for
that it both breathes and chirps in the egg be-
fore its exclusion is most certain.
The membranes serve to include the fluids,
and therefore are they present in the same num-
ber as these, and therefore is«the colliquament
also invested, as soon as it is produced, with
a tunica propria, which Aristotle refers to in
these words: "A membrane covered with rami-
fications of blood-vessels already surrounds the
clear liquid/'1 &c. But the exit of the chick
being at hand, and the albumen and colliqua-
1 History of Animals, vi. 3.
ment being entirely consumed, all the mem-
branes, except that which surrounds the vitel-
lus, are dried up and disappear; the membrana
vitelli, on the contrary, along with the yelk, is
retracted into the peritoneum of the chick and
included in the abdomen. Of the membranes
two are common to the whole egg, which they
surround immediately under the shell; the rest
belong, one to the albumen, one to the yelk,
one to the colliquament; but all still conduce to
the preservation and separation of the parts
they surround. The outer of the two common
membranes which adheres to the shell is the
firmer, that it may take no injury from the
shell; the inner one again is smooth and soft,
that it may not hurt the fluids; in the same
way, therefore, as the meninges of the brain
protect it from the roughness of the superin-
cumbent skull. The internal membranes, as I
have said, include and keep separate their pe-
culiar fluids, whence they are extremely thin,
pellucid, and easily torn.
Fabricius ascribes great eminence and dignity
to the chalazae, regarding them as the parts
whence the chick is formed; he, however, leaves
the spot or cicatricuia connected with the mem-
brana vitelli without any office whatsoever,
looking on it merely as the remains of the pe-
duncle whence the vitellus was detached from
the vitellarium in the superior uterus of the
hen. In his view the vitellus formerly obtained
its nourishment either by this peduncle or the
vessels passing through it; but when detached,
and no longer nourished by the hen, a simple
trace of the former connexion and important
function alone remains.
I, however, am of opinion that the uses of
the chalazae are no other than those I have as-
signed them, namely, that they serve as poles
to the microcosm of the egg, and are the asso-
ciation of all the membranes convoluted and
twisted together, by which not only are the
several fluids kept in their places, but also in
their distinct relative positions. But I have ab-
solute assurance that the spot or cicatricula in
question is of the very highest importance; it is
the part in which the calor insitus nestles; where
the first spark of the vital principle is kindled;
for the sake of which, in a word, the whole of
the rest of the fluids and all the membranes of
the egg are contrived. But this has been al-
ready insisted on above.
Formerly, indeed, I did think with Fabricius
that this cicatricula was the remains or trace of
the detached peduncle; but I afterwards learned
by more accurate observation that this was not
468
WILLIAM HARVEY
the case; that the peduncle, by which the vitel-
lus hangs, was infixed in no such limited space
as we find it in apples and plums, and in such a
way as would have given rise to a scar on its
separation. This peduncle, in short, expands
like a tube from the ovary on towards the vitel-
lus, the horizon of which it embraces in a bipar-
tite semicircle, not otherwise than the tunica
conjunctiva embraces the eye; and this in such-
wise that the superior part of the vitellus, or
the hemisphere which regards the ovary, is al-
most free from any contact or cohesion with
the peduncle, in the superior part of the cup or
hollow of which nevertheless, but somewhat to
the side, the spot or cicatricula in question is
placed. The peduncles becoming detached from
the vitelli can therefore in no way be said to
leave any trace of their attachments behind
them. Of the great importance of this spot in
generation I have already spoken in the his-
torical portion of my work.
But I have still, always following my old
teacher Fabricius as my guide on the way, to
treat of the uses of the cavity in the blunt end
of the egg.
Fabricius enumerates various conveniences
arising from this cavity, according to its dimen-
sions. I shall be brief on the subject: it contains
air, and is therefore useful in the ventilation of
the egg, assisting the perspiration, refrigeration,
and respiration, and finally the chirping of the
chick. Whence this cavity, small at first, is
larger by and by, and at last becomes of great
size, as the several offices mentioned come into
play.
Thus far have we spoken of the generation of
the egg and chick, and of the uses of the several
parts of the egg; and to the type exhibited we
have referred the mode of generation of ovipa-
rous animals in general. We have still to speak
of the generation of viviparous animals, in
doing which we shall as before refer all to a
single familiarly known species.
EXERCISE 62. An egg is the common origin
of all animals
"Animals,** says Aristotle,1 "have this in
common with vegetables, that some of them
arise from seed, others arise spontaneously; for
as plants either proceed from the seed of other
plants, or spring up spontaneously, having met
with some primary condition fit for their evolu-
tion, some of them deriving their nourishment
from the ground, others arising from and living
on other plants; so are some animals engendered
1 History of 'Animals, v. i.
from cognate forms, and others arise spontane-
ously, no kind of cognate seed having preceded
their birth; and whilst some of them are gen-
erated from the earth, or putrefying vegetable
matter, like so many insects, others are pro-
duced in animals themselves and from the ex-
crementitious matters of their parts." Now the
whole of these, whether they arise spontane-
ously, or from others, or in others, or from the
parts or excrements of these, have this in com-
mon, that they are engendered from some prin-
ciple adequate to this effect, and from an effi-
cient cause inherent in the same principle. In
this way, therefore, the primordium from which
and by which they arise is inherent in every
animal. Let us entitle this the primordium veg-
etale or vegetative incipience, understanding by
this a certain corporeal something having life
in potentia; or a certain something existing per
se, which is capable of changing into a vegeta-
tive form under the agency of an internal prin-
ciple. Such primordia are the eggs of animals
and the seeds of plants; such also are the con-
ceptions of viviparous animals, and the worm,
as Aristotle calls it, whence insects proceed: the
primordia of different living things consequent-
ly differ from one another; and according to
their diversities are the modes of generation of
animals, which nevertheless all agree in this one
respect, that they proceed from the vegetal
primordium as from matter endowed with the
virtue of an efficient cause, though they differ
in respect of the primordium which either bursts
forth, as it were, spontaneously and by chance,
or shows itself as fruit or seed from something
else preceding it. Whence some animals are
spoken of as spontaneously produced, others
as engendered by parents. And these last are
again distinguished by their mode of birth, for
some are oviparous, others viviparous, to which
Aristotle2 adds a vermiparous class. But if we
take the thing as simple sense proclaims it,
there are only two kinds of birth, inasmuch as
all animals engender others either in actu — vir-
tually, or in potentia— potentially. Animals
which bring forth in fact and virtually are
called viviparous, those that bring forth poten-
tially are oviparous. For every primordium that
lives potentiallyi we, with Fabricius, think
ought to be called an egg, and we make no dis-
tinction between the worm of Aristotle and an
egg, both because to the eye there is no differ-
ence, and because the identity is in conformity
with reason. For the vegetal primordium which
lives potentially is also an animal potentially.
* History of Animals, i. 5.
ANIMAL GENERATION
469
Nor can the distinction which Aristotle made
between the egg and the worm be admitted:
for he defines an egg to be that "from part of
which an animal is produced";1 whilst that, he
says elsewhere, "which is totally changed, and
which does not produce an animal from a part
only, is a worm."2 These bodies, however, agree
in this, that they are both inanimate births, and
only animals potentially; both, consequently,
are eggs.
And then Aristotle himself, whilst he speaks
of worms in one place, designates them by the
name of eggs in another.3 Treating of the locust,
he says, "its eggs become spoiled in autumn
when the season is wet";4 and again, speaking
of the grasshopper, he has these words: "when
the little worm has grown in the earth it be-
comes a matrix of grasshoppers (tettigometra)" \
and immediately afterwards, "the females are
sweeter after coitus, for then they are full of
white eggs."
In this very place, indeed, where he distin-
guishes between an egg and a worm, he adds:
"but the whole of this tribe of worms, when
they have come to their full size, are changed
in some sort into eggs; for their shell or cover-
ing hardens, and they become motionless for a
season, a circumstance that is plainly to be seen
in the vermiculi of bees and wasps, and also in
caterpillars."8 Everyone indeed may observe
that the primordia of spiders, silkworms, and
the like, are not less to be accounted eggs than
those of the Crustacea and mollusca, and almost
all fishes, which are not actually animals, but
are potentially possessed of the faculty of pro-
ducing them. Since, then, those creatures that
produce actually are called viviparous, and
those that produce potentially either pass with-
out any general distinguishing title or are called
oviparous and particularly as such productions
are vegetal primordia, analogous to the seeds of
plants, which true eggs must needs be held to
be, the conclusion is that all animals are either
viviparous or oviparous.
But as there are many species of oviparous
animals, so must there also be several species of
eggs; for every primordium is not alike fit to
receive or assume every variety of animal form
indifferently. Though we admit, therefore, that
eggs in a general sense do not differ, yet when
we find that one is perfect, another imperfect,
1 On the Generation of Animate, in. 9.
8 History of 'Animals, i. 5.
* Ibid., v. 29.
4 Ibid., v. 30.
1 On the Generation of Animals, in. 9.
it is obvious that they differ essentially from
one another. Perfect eggs are such as are com-
pleted in the uterus, where they obtain their
due dimensions before being extruded; of this
kind are the eggs of birds. Imperfect eggs, again,
are such as are prematurely excluded before
they are of the full size, but increase after they
are laid ; of this description are the eggs of fishes,
Crustacea and mollusca; the primordia of in-
sects, which Aristotle entitles worms, are fur-
ther to be referred to this class, as well as the
primordia of those animals that arise sponta-
neously.
Moreover, although perfect eggs are of two
colours, in other words, are composed of albu-
men and vitellus, some are still only of one
hue, and consist of albumen alone. In like man-
ner, of imperfect eggs, some from which a per-
fect animal proceeds are properly so called;
such are the eggs of fishes; others are improper-
ly so styled, they engendering an imperfect
animal, namely, a worm, grub, or caterpillar, a
kind of mean between a perfect and an imper-
fect egg, which, in respect of the egg or the
primordium itself, is an animal endowed with
sense and motion, and nourishing itself; but in
respect of a fly, moth or butterfly, whose pri-
mordium it is potentially, it is as a creeping
egg, and to be reputed as adequate to its own
growth; of this description is the caterpillar,
which having at length completed its growth is
changed into a chrysalis or perfect egg, and
ceasing from motion, it is like an egg, an animal
potentially.
In the same way, although there are some
eggs from the whole of which a perfect animal
is produced by metamorphosis, without being
nourished by any remains of the substance of
the egg, but forthwith finds food for itself
abroad, there are others from one part of which
the embryo is produced, and from the remain-
der of which it is nourished — although, I re-
peat, there are such differences among eggs,
still, if we be permitted to conclude on the
grounds of sense and analogy, there is no good
reason wherefore those that Aristotle calls
worms should not be spoken of as eggs; inas-
much as all vegetal principles are not indeed
animals actually, but are so potentially, are
true animal seeds, analogous to the seeds of
vegetables, as we have already demonstrated in
the particular instance of the hen's egg. All ani-
mals are, therefore, either viviparous or ovipa-
rous, inasmuch as they all either produce a liv-
ing animal in fact, or an egg, rudiment, or pri-
mordium, which is an animal potentially.
470
WILLIAM HARVEY
The generation of all oviparous animals may
therefore be referred to that of the hen's egg as
a type, or at all events deduced from thence
without difficulty, the same things and inci-
dents that have been enumerated in connexion
with the common fowl being also encountered
in all other oviparous animals whatsoever. The
various particulars in which they differ one
from another, or in which they agree, either
generally, or specifically, or analogically, will
be subsequently treated of when we come to
speak of the generation of insects and the ani-
mals that arise equivocally. For as every gener-
ation is a kind of way leading to the attainment
of an animal form, as one race of animal is more
or less like or unlike another, their constituent
parts either agreeing or disagreeing, so does it
happen in respect of their mode of generation.
For perfect Nature, always harmonious with
herself in her works, has instituted similar parts
for similar ends and actions: to arrive at the
same results, to attain the same forms, she has
followed the same path, and has established one
and the same method in the business of genera-
tion universally.
Wherefore as we still find the same parts in
the perfect or two-coloured egg of every bird,
so do we also observe the same order and method
pursued in the generation and development of
their embryos as we have seen in the egg of the
common fowl. And so also are the same things
to be noted in the eggs of serpents and of rep-
tiles, or oviparous quadrupeds, such as tortoises,
frogs, and lizards, from all the perfect two-col-
oured eggs of which embryos are produced and
perfected in the same manner. Nor is the case
very different in regard to fishes. But of the
manner in which spiders and the Crustacea,
such as shrimps and crabs, and the mollusca,
such as the cuttlefish and calamary, arise from
their eggs; of the conditions also upon which
worms and grubs first proceed from the eggs
of insects, which afterwards change into chrys-
alides or aurelias, as if they reverted anew to
the state of eggs, from which at length emerge
flies or butterflies— of the several respects in
which these differ in their mode of generation
from an egg, from what we have found in the
hen's egg, will be matter for remark in the
proper place.
Although all eggs consisting of yelk and white
are not produced and fecundated in the same
manner, but some are made prolific through
the intercourse of male and female, and others
in some other way (as of fishes); and although
there is some difference even in the mode in
which eggs grow, some attaining maturity with-
in the body of the parent, others continuing to
be nourished and to grow when extruded, there
is still no reason why an embryo should not be
developed in the same precise manner in every
egg — always understood as perfect — as it is in
the egg of the hen. Wherefore the history which
has been given of the evolution of the chick
from the hen's egg may be regarded as applicable
to the generation of all other oviparous animals
whatsoever, as well as to the inferences or con-
clusions which may be deduced from thence.
EXERCISE 63. Of the generation of viviparous
animals
Thus far have we treated mainly of the gen-
eration of oviparous animals; we have still to
speak particularly of the other species of gen-
eration, the viviparous, to wit, in which many
things identical with those we have noticed in
oviparous generation will come to be observed.
These we have reduced into order, and here at
length present for consideration. Even the
parts that appear paradoxical and in contradic-
tion with the current views of generation will,
I believe, be found entirely in conformity with
truth.
Among viviparous animals, man, the most
perfect of all creatures, occupies the foremost
place; after him come our ordinary domestic
animals, of which some are soliped, such as the
horse and ass; others bisulcate, as the ox, goat,
sheep, deer, and hog; others digitate, such as
the dog, cat, rabbit, mouse, and others of the
same description; from the modes of whose
generation a judgment may be formed of that
of all other viviparous animals. Wherefore I
shall propose a single genus, by way of general
example or type, as we did in the case of the
oviparous class; this made familiar to us, will
serve as a light or standard, by means of which
all the others may be judged of by analogy.
The reasons that led me to select the hen's
egg as the measure of eggs in general have been
already given: eggs are of little price, and are
everywhere to be obtained, conditions that
permit repeated study, and enable us cheaply
and readily to test the truth of statements
made by others.
We have not the same facilities in studying
the generation of viviparous animals: we have
rarely, if ever, an opportunity of dissecting the
human uterus; and then to enter on the sub-
ject experimentally in the horse, ox, sheep,
goat, and other cattle, would be attended with
immense labour and no small expense; dogs,
ANIMAL GENERATION
47*
cats, rabbits, and the like, however, will supply
those with subjects who are desirous of putting
to the test of experiment the matters that are
to be delivered by us in this place.
Fabricius of Aquapendente, as if every con-
ception of a viviparous animal were in a certain
sense an egg, begins his treatise with the egg as
the universal example of generation; and among
other reasons for his conclusions assigns this in
particular: "Because the study of the egg has
the most extensive application, the greater
number of animals being engendered from
eggs.*'1 Now we, at the very outset of our ob-
servations, asserted that ALL animals were in
some sort produced from eggs. For even on the
same grounds, and in the same manner and or-
der in which a chick is engendered and devel-
oped from an egg, is the embryo of viviparous
animals engendered from a pre-existing concep-
tion. Generation in both is one and identical in
kind: the origin of either is from an egg, or at
least from something that by analogy is held
to be so. An egg is, as already said, a conception
exposed beyond the body of the parent, whence
the embryo is produced; a conception is an egg
remaining within the body of the parent until
the foetus has acquired the requisite perfection;
in everything else they agree; they are both
alike primordially vegetables, potentially they
are animals. Wherefore, the same theorems and
conclusions, though they may appear paradox-
ical, which we drew from the history of the egg,
turn out to be equally true with regard to the
generation of animals generally. For it is an ad-
mitted fact that all embryos, even those of man,
are procreated from some conception or primor-
dium. Let us, therefore, say that that which is
called primordium among things arising spon-
taneously, and seed among plants, is an egg
among oviparous animals, /. ^., a certain cor-
poreal substance, from which, through the mo-
tions and efficacy of an internal principle, a
plant or an animal of one description or another
is produced; but the prime conception in vivip-
arous animals is of the same precise nature, a
fact which we have found approved both by
sense and reason.
What we have already affirmed of the egg,
viz., that it was the sperma or seed of animals
and analogous to the seeds of plants, we now
affirm of the conception, which is indeed the
seed of an animal, and therefore also properly
called ovum or egg. Because "a true seed," ac-
cording to Aristotle,2 "is that which derives its
1 Deform, ovi et pulh, i .
* On the Generation of Animals, i. 18.
origin from the intercourse of male and female,
and possesses the virtues of both; such as is the
seed of all vegetables, and of some animals, in
which the sexes are not distinct, and is, as that
which is first mingled from male and female, a
kind of promiscuous conception or animal; for
it has those things already that are recognized
of both"; i. <?., matter adapted to nourish the
foetus, and a plastic or formative and effective
virtue. And so in like manner is a conception
the fruit of the intercourse of male and female,
and the seed of the future embryo; it therefore
does not differ from an egg.
"But that which proceeds from the generant
is the cause which first obtains the principle of
generation (/. £., it is the efficient cause), and
ought to be called the geniture,"8 not the seed,
as is commonly done both by the vulgar and
philosophers at the present time; because it has
not that which is required of both the concur-
ring agents, neither *is it analogous to the seeds
of plants. But whatever possesses this, and cor-
responds to the seeds of vegetables, that too is
rightly entitled egg and conception.
Further, the definition of an egg, as given by
Aristotle, is perfectly applicable to a concep-
ttion: "An egg," he says, "is that, the principal
part of which goes to constitute an animal, the
remainder to nourish the animal so consti-
tuted."4 Now the same thing is common to a
conception, as shall be made to appear visibly
from the dissection of viviparous animals.
Moreover, as the chick is excluded from the
egg under the influence of warmth derived
from the incubating hen or obtained in any
other way, even so is the foetus produced from
the conception in the uterus under the genial
warmth of the mother's body. In few words, I
say, that what oviparous animals supply by
their breast and incubation, viviparous animals
afford by their uterus and internal embrace.
For the rest, in all that respects the develop-
ment, the embryo is produced from the con-
ception in the same manner and order as the
chick from the egg, with this single difference,
that whatever is required for the formation and
growth of the chick is present in the egg, whilst
the conception, after the formation of the em-
bryo, derives from the uterus of the mother
whatever more is requisite to its increase, by
which it continues to grow in common with the
foetus. The egg, on the contrary, becomes more
and more empty as the chick increases; the
nutriment that was laid up in it is diminished;
*/*&
4 History of Animals, i. 5*
472
WILLIAM HARVEY
nor does the chick receive aught in the shape of
new aliment from the mother; whilst the foetus
of viviparous animals has a continued supply,
and when born, moreover, continues to live
upon its mother's milk. The eggs of fishes, how-
ever, increase through nourishment obtained
from without; and insects and crustaceous and
molluscous animals have eggs that enlarge after
their extrusion. Yet are not these called eggs
the less on this account, nor, indeed, are they
therefore any the less eggs. In like manner the
conception is appropriately designated by the
name of ovum or egg, although it requires and
procures from without the variety of aliment
that is needful to its growth.
Fabricius gives this reason for some animals
being oviparous, for all not producing living
offspring: "It is," he says, "that eggs detained
in the uterus till they had produced their chicks
would interfere with the flight of birds, and
weigh them down by their weight." Serpents
would also be hindered in their alternate zig-
zag movements by a multitude of eggs in the
abdomen. In the body of tortoises, with their
hard and girding shell, there is no room for any
store or increase of eggs; nor would the abdo-
men of fishes suffice for the multitude of eggt
they must spawn were these to grow to any
size. It was, therefore, matter of necessity that
those creatures should lay their eggs imperfect.
It seems most natural that an animal should re-
tain and cherish its conception in its interior
until the foetus it produces has come to matu-
rity; but Nature sees herself compelled, as it
were, occasionally to permit the premature
birth of various eggs, and to provide them,
without the body of the parent, with the nour-
ishment they require for their complete de-
velopment. As to everything that refers to the
evolution of the foetus, all animals are engen-
dered from an oviform primordium; I say ovi-
form, not as meaning that it has the precise
configuration of an egg, but the nature and
constitution of one; this being common in gen-
eration, that the vegetal primordium whence
the foetus is produced, including the nature of
an egg, corresponding in its proportions to the
seed of a plant, pre-exists. In all vegetal pri-
mordia, consequently, whether eggs, or having
the form of eggs, there are inherent the nature
and conditions of an egg, properties which the
seeds of plants have in common with the eggs
of animals. The primordium of any animal,
whatsoever, is therefore called seed and fruit;
and in like manner the seed of every plant is
spoken of as a kind of conception or egg.
And this is the reason why Aristotle says:
"Animals that engender internally have some-
thing formed in the fashion of an egg after their
first conception: there is a fluid contained with-
in a delicate membrane, like an egg without the
shell. And this is the cause why the disorders of
the conception, which are apt to occur in the
early period, are called discharges."1 Such a
discharge is particularly observed among women
when they miscarry in the course of the first
or second month. I have repeatedly seen such
ova aborted at this time; and such was the one
which Hippocrates has described as having
been thrown off by the female pipe-player in
consequence of a fall.
In the uterus of all animals there is, conse-
quently, present a prime conception or primor-
dium, which, on Aristotle's testimony, "is like
an egg surrounded with a membrane from which
the shell had been removed."2 This fact will ap-
pear still more plainly from what is about to be
said. Meantime let us conclude with the philos-
opher, "that all living creatures, whether they
swim, or walk, or fly, and whether they come
into the world with the form of an animal or of
an egg, are engendered in the same manner."
EXERCISE 64. The generation of viviparous ani-
mals in general is illustrated from the history of that
of the hind and doe, and the reason of this selection
It was customary with his Serene Majesty,
King Charles, after he had come to man's es-
tate, to take the diversion of hunting almost
every week, both for the sake of finding relaxa-
tion from graver cares, and for his health; the
chase was principally the buck and doe, and no
prince in the world had greater herds of deer,
either wandering in freedom through the wilds
and forests, or kept in parks and chases for this
purpose. The game during the three summer
months was the buck, then fat and in season;
and in the autumn and winter, for the same
length of time, the doe. This gave me an oppor-
tunity of dissecting numbers of these animals
almost every day during the whole of the sea-
son when they were rutting, taking the male,
and falling with young; I had occasion, so often
as I desired it, to examine and study all the
parts, particularly those dedicated to the offices
of generation.
I shall therefore consider the generation of
viviparous animals in general, from the particu-
lar history of the hind and doe, as the instance
most convenient to me; and, as I have done
1 On the Generation of Animals, in. 9.
2 History of Animals, vn. 7.
ANIMAL GENERATION
473
above, in speaking of oviparous generation,
where I have referred everything to the com-
mon fowl, so shall I here, in discussing vivipa-
rous generation, refer all to the fallow deer and
roe. In taking this course, I am not moved by
the same reasons as I was in reference to the
hen's egg; but because the great prince, whose
physician I was, besides taking much pleasure
in such inquiries, and not disdaining to bear
witness to my discoveries, was pleased in his
kindness and munificence to order me an abun-
dant supply of these animals and repeated op-
portunities of examining their bodies.
I therefore propose to give the history of gen-
eration in the hind and doe as I have observed
it during a long series of years, and as most fa-
miliar to me, believing that from thence some-
thing certain in reference to the generation of
other viviparous animals may be concluded. In
giving a faithful narrative of this history, I shall
not abstain in its course from introducing par-
ticulars worthy of note that have either been
observed accidentally and by the way, or that
are the result of particular dissections instituted
for the purpose of arriving at conclusions, the
subjects of these having been other bisulcated,
hoofed, or multtmgulated animals, or, finally,
man himself. We shall give a simple narrative
of the series of formations of the foetus, follow-
ing the footsteps of nature in the process.
EXERCISE 65. Of the uterus of the hind and doe
About to treat of the generation of the hind
and doe, our first business will be to speak of the
place where it proceeds, or of the uterus, as we
have done above, in giving the history of the
common fowl, by which all that follows will be
more easily and readily understood. And his-
tory has this great pre-eminence over fable,
that it narrates the events which transpired in
certain places at certain times, and therefore
leads us to knowledge by a safe and assured way.
Now that we may have a clearer idea of the
uterus of the hind, I shall describe both its ex-
ternal and internal structure, following the
uterus of the human female as my guide. For
man is the most consummate of creatures, and
has therefore the genital as well as all other
parts in higher perfection than any other ani-
mal. The parts of the female uterus consequent-
ly present themselves with great distinctness,
and by reason of the industry of anatomists in
this direction are believed to be particularly
well known to us.
We meet with many things in the uterus of
deer which we encounter in the uterus of the
human female; and we also observe several that
differ. In the vulva or os externum we find
neither labia, nor clitoris, nor nymphae, but
only two openings, one for the urine, adjacent
to the pec ten, or os pubis, the other the vagina,
lying between the meatus urinarius and the
anus. A cuticular or membranous fold, such as
we have noted in the hen, stretching down-
wards from the anus, acts as a velabrum, sup-
plies the place of nymphae and labia pudendi,
and guards against injury from without. This
velabrum must be somewhat retracted by the
female when she copulates, or at all events must
be raised by the penis of the male as it enters
the vulva.
The symphysis pubis being divided in deer,
and the legs widely separated, the urinary blad-
der, the vagina which is entered by the penis
of the buck, and the cervix uteri, are all seen in
their relative situations, not otherwise than
they are in women; the ligamenta suspensoria,
with the veins, arteries, and testicles, as they
are called, also come into sight; the cornua of
the uterus in these creatures are also more re-
markable than any other part of this organ.
As for the vessels called vasa praeparantia and
vasa deferentia seu ejaculantia, you will dis-
cover nothing of the kind here, nor indeed in
any other female animal that I am aware of.
The anatomists who believe that women emit a
seminal fluid sub coitu have been too eager in
their search after such vessels; for in some they
are not met with at all, and where they do oc-
cur they never present themselves with any-
thing of uniformity of character. Wherefore it
seems most likely that women do not emit any
semen sub coitu, which is in conformity as I
have said with what the greater number of
women state. And although some of warmer
temperament shed a fluid in the sexual em-
brace, still that this is fruitful semen, or is a
necessary requisite to conception, I do not be-
lieve; for many women conceive without hav-
ing any emission of the kind, and some even
without any kind of pleasurable sensation what-
soever. But of these things more in another
place.
The vulva, or vagina uteri, which extends
from the os externum to the inner orifice of the
uterus, is situated in the hind, as well as in the
human female, between the urinary bladder
and the intestinum rectum, and corresponds in
length, width, and general dimensions, with
the penis of the male. When this part is laid
open it is found occupied lengthwise by rugae
and furrows, admitting of ready distension, and
474
WILLIAM HARVEY
lubricated with a sluggish fluid. At its bottom
we observe a very narrow and small orifice, the
commencement of the cervix uteri, by which
whatever is propelled outwards from the cavity
of the uterus must pass. This is the correspond-
ing orifice to that which medical men assert is
so firmly closed and sealed up in the pregnant
woman and virgin, that it will not even admit
the point of a probe or fine needle.
The os uteri is followed by the cervix or proc-
ess, which is much longer and rounder than in
woman, and also more fibrous, thicker, and
nervous; it extends from the bottom of the va-
gina to the body of the uterus. If this cervix
uteri be divided longitudinally, you perceive
not only its external orifice at the bottom of
the vagina, its surface in close contact, and so
firmly agglutinated that not even air blown in-
to the vagina will penetrate the cavity of the
uterus, but five other similar constrictions
placed in regular order, firmly contracted against
the entrance of any foreign body and sealed
with gelatinous mucus; just as we find the nar-
row orifice of the woman's uterus plugged with
a yellowish glutinous mass. A like constriction
of parts, all firmly closed, and precluding all
possibility of entrance, Fabricius has found in
the uterine neck of the sheep, sow, and goat. In
the deer there are very distinctly five of these
constrictions, or so many orifices of the uterus
constricted and conglutinated, which may all
j ustly be looked upon as so many barriers against
the entrance of anything from without. Such
particular care has nature taken, that if the first
barrier were forced by any cause or violence,
the second should still stand good, and so the
third, and the fourth, and the fifth, determined
apparently that nothing should enter. A probe
pushed from within outwards, however, from the
cavity of the uterus towards the vagina, passes
through readily. A way had to be left open for
the escape of flatus, menstrual blood, and other
excreted fluids; but even the smallest and most
subtile things, air, for instance, and the seminal
fluid are precluded all access from without.
In all animals this uterine orifice is found
obstructed or plugged up in the same way as it
is wont to be in women, among whom we have
sometimes known the outlet so much constricted
that the menses, lochia, and other humours
were retained in the womb, and became the
exciting cause of most severe hysterical symp-
toms. In such cases it became necessary to con-
trive a suitable instrument with which the os
uteri being opened, the matters that stagnated
within were discharged, when all the accidents
disappeared. By this contrivance injections
could also be thrown into the cavity of the
uterus, and by means of these I have cured in-
ternal ulcers of the womb, and have occasion-
ally even found a remedy for barrenness.
The cavity of the uterus in the deer is ex-
tremely small, and the thickness of its walls not
great; the body of the womb in these animals
is, in fact, but a kind of vestibule, or ante-room,
in the cavity of which a passage opens to the
right and left into either cornu.
For the parts are different in almost all ani-
mals from what they are in woman, in whom
the principal part of the uterus is its body, and
the cervix and cornua are mere appendices,
that scarcely attract attention. The neck is
short; the cornua are slender round processes
extending from the fundus uteri like a couple of
tubes, which anatomists indeed commonly speak
of as the vasa ejaculatoria. In the deer, how-
ever, as in all other quadrupeds, except the ape
and the solipeds, the chief organ of generation
is not the body but the horns of the uterus. In
the human female and the solipedia, the uterus
is the place of conception, in all the rest the
conception is perfected in the cornua; and this
is the reason why writers so commonly speak
of the cornua uteri in the lower animals under
the simple name of the uterus, saying that the
uterus in certain animals is bipartite, whilst in
others it is not, understanding by the word
uterus the place in which conception takes
place, this in the majority of viviparous and
especially of multiparous animals being the cor-
nua, to which, moreover, all the arteries and
veins distributed to the organs of generation are
sent. We shall, therefore, in treating of the his-
tory of generation in the deer employ the words
uterus and horns of the uterus promiscuously.
In the human female, as I have said, the two
tubes that arise near the cervix uteri and there
perforate its cavity have no analogy to the parts
generally called cornua, but, on the contrary,
in the mind of some anatomists, to the vasa
spermatica. By others again they are called the
spiramenta uteri— the breathing tubes of the
uterus; and by others still they are called the
vasa deferentia seu reservantia, as if they were
of the same nature as the canals so designated in
the male; whilst they in fact correspond to the
cornua of the uterus in other animals, as most
clearly appears from their situation, connexion,
length, perforation, general resemblance, and
also office. For as many of the lower animals
regularly conceive in the cornua uteri, so do
women occasionally carry their conceptions in
ANIMAL GENERATION
475
the cornu, or this tube, as the learned Riolanus1
has shown from the observations of others, and
as we ourselves have found it with our own eyes.
These cornua terminate in a common cavity
which, as stated, forms a kind of porch or vesti-
bule to the uterus, and corresponds in the deer
to the neck of the womb in women; in the same
way as the tubes in question in the human fe-
male correspond to the cornua uteri in the deer.
Now this name of cornua has been derived from
the resemblance of the parts to the horns of an
animal; and in the same way as the horns of a
goat or ram are ample at the base, arched and
protuberant in front, and bent-in behind, so
are these horns of the uterus in the hind and doe
capacious inferiorly, and taper gradually off
superiorly, as they are reflected towards the
spine. Further, as the horns of the animal are
unequally tuberculated and uneven in front,
but smooth behind, so are the horns of the
uterus tuberculated, as it were, and uneven,
through the presence of cells, something like
those of the colon, inferiorly and anteriorly;
but superiorly, and on the aspect towards the
spine, they are continuous and smooth, and
present themselves secured and bound down by
a ligamentous band; they at the same time
gradually decrease in size like horns. Did one
take a piece of empty intestine, such as is used
for making sausages, and drawing a tape through
it, tied this on one side, he would have it puck-
ered and constricted on that side, and thrown
into cells similar to those of the colon on the
opposite side. Such is the structure of the cor-
nua of the uterus in the hind and doe. In other
animals it is different; for there the cells are
either much larger, or they are entirely want-
ing. The cells of the cornua uteri of the hind
and doe, however, are not all of the same size;
the first that is met with is much larger than
any of the others; and here it is that the concep-
tion is generally lodged.
As the uterus, tubes, or cornua, and other
parts appertaining in the human female are
connected with the pubes, spine, and surround-
ing structures by the medium of broad and
fleshy membranes, by suspensory bands, as it
were, which anatomists have designated by the
name of bats1 wings, because they have found
that the uterus suspended in this way resem-
bled a bat with its wings expanded, so also are
the cornua uteri, together with the testes [ova-
ries], on either side, and all the uterine vessels,
connected with the neighbouring parts, partic-
ularly with the spine, by means of a firm mem-
1 AntJtrvpologiat n. 34.
brane, within the folds of which are suspended
all the parts that have been mentioned, and
which serves the same office with reference to
these uterine structures as the mesentery does
to the intestines, and the mesometrium to the
uterus of the fowl. In the same way, too, as the
mesenteric arteries and veins are distributed to
the intestines through the mesentery, are the
uterine vessels distributed to the uterus through
the membrane in question; in which also cer-
tain vessels and glands are perceived on either
side, which by anatomists are generally desig-
nated the testicles [the ovaries].
The substance of the horns of the uterus in
the hind and doe is skinny or fleshy, like the
coats of the intestines, and has a few very mi-
nute veins ramified over it. This substance you
may in anatomical fashion divide into several
layers, and note different courses of its com-
ponent fibres, fitting them to perform the sev-
eral motions and actions required, retention,
namely, and expulsion. I have myself frequent-
ly seen these cornua moving like earthworms,
or in the manner in which the intestines may at
any time be observed, twisting themselves with
an undulatory motion, on laying open the ab-
domen of a recently slaughtered animal, by
which they move on the chyle and excrements
to inferior portions of the gut, as if they were
surrounded and compressed with a ring forced
over them, or were stripped between the fingers.
The uterine veins, as in woman, all arise from
the vena cava, near the emulgents; the arteries
(and this also is common to the deer and the
human subject) arise from the crural branches
of the descending aorta. And as in the pregnant
woman the uterine vessels are relatively larger
and more numerous than in any other part of
the body, this is likewise the case in the preg-
nant hind and doe. The arteries, however, con-
trary to the arrangement in other parts of the
body, are much more numerous than the veins;
and air blown into them makes its way into the
neighbouring veins, although the arteries cannot
be inflated in their turn by blowing into the
veins. This fact I also find mentioned by Master
Riolanus; and it is a cogent argument for the
circulation of the blood discovered by me; for
he clearly proves that whilst there is a passage
from the arteries into the veins, there is none
backwards from the veins into the arteries. The
arteries are more numerous than the veins, be-
cause a large supply of nourishment being re-
quired for the foetus, it is only what is left un-
used that has to be returned by the latter
channels.
476
WILLIAM HARVEY
In the deer as well as in the sheep, goat, and
bisulcate animals generally, we find testicles;
but these are mere little glands, which rather
correspond in their proportions to the prostate
or mesenteric glands, the use of which is to
establish divarications for the veins, and to store
up a fluid for lubricating the parts, rather than
for sec re ting semen, concocting it in to fecundity,
and shedding it at the time of intercourse. I am
myself especially moved to adopt this opinion,
as well by numerous reasons which will be ad-
duced elsewhere, as by the fact that in the rut-
ting season, when the testes of the buck and
hart enlarge and are replete with semen, and
the cornua of the uterus of the hind and doe are
greatly changed, the female testicles, as they
are called, whether they be examined before or
after intercourse, neither swell nor vary from
their usual condition; they show no trace of
being of the slightest use either in the business
of intercourse or in that of generation.
It is surprising what a quantity of seminal
fluid is found in the vesiculae seminales and tes-
ticles of moles and the larger kinds of mice at
the season of intercourse; this circumstance cor-
responds with what we have already noticed in
the cock, and the great change perceptible in the
organs of generation of both sexes; nevertheless,
the glands, which are regarded as the female tes-
tes, continue all the while unchanged and with-
out departure from their pristine appearance.
All that has now been said of the uterus and
its horns in hinds and does applies in major part
to viviparous animals in general, but not to the
human female, inasmuch as she conceives in the
body of the uterus, but all these, with the ex-
ception of the horse and ass, in the horns of the
organ; and even the horse and ass, although
they appear to carry their fruit in the uterus,
still is the f lace of the conception in them rather
of the nature of an uterine horn than the uter-
ine body. For the place here is not bipartite
indeed, but it is oblong, and different from the
human uterus both in its situation, connex-
ions, structure, and substance; it bears a greater
affinity to the superior uterus or uterine process
of the fowl, where the egg grows and becomes
surrounded with the albumen, than to the
uterus of the woman.
EXERCISE 66. Of the intercourse of the hind
and doe
So much for the account of the uterus of the
female deer, where we have spoken briefly upon
all that seemed necessary to the history of gen-
eration, viz.9 the place of conception, and the
parts instituted for its sake. We have still to
speak of the action and office of this place, in
other words, of intercourse and conception.
The hind and doe admit the male at one and
only one particular season of the year, namely,
in the middle of September, after the Feast of
the Holy Cross; and they bring forth after the
middle of June, about the Feast of St. John the
Baptist (24th June). They, therefore, go with
young about nine months, not eight, as Pliny
says;1 with us, at all events, they produce in the
ninth month after they have taken the buck.
At the rutting season the bucks herd with
the does; at other times they keep severally
apart, the males, particularly the older ones, as-
sociating together, and the females and younger
males trooping and feeding in company. The
rutting season lasts for a whole month, and it
begins later if the weather have been dry, earlier
if it have been wet. In Spain, as I am informed,
the deer are hardly in rut before the beginning
of October, wet weather not usually setting in
there until this time; but with us the rutting
season rarely continues beyond the middle of
October.
At this time deer are rendered savage by de-
sire, so that they will attack both dogs and men,
although at other seasons they are so timid and
peaceable, and immediately betake themselves
to flight on the barking of even the smallest dog.
Every male knows all his own females, nor
will he suffer any one of them to wander from
his herd: with a run he speedily drives back any
straggler; he walks jealously from time to time
among his wives; looks circumspectly about
him, and the careful guardian of his own, he
shows himself the watchful sentinel. If a strange
doe commit any offence, he does not pursue
her very eagerly, but rather suffers her to get
away; but if another buck approach he instant-
ly runs to meet him, and gives him battle with
his antlers.
The hind and doe are held among the num-
ber of the chaster animals; they suffer the ad-
dresses of the male reluctantly, who, like the
bull, mounts with violence, and unless forced
or tired out, they resist him; which disinclina-
tion of the females appears also to be the reason
of their herding together, and confining them-
selves to their own males, who are always the
older and better armed; for when any strange
male approaches them they immediately take
to flight, and seek refuge in their own herd, and
protection to their chastity, as it seems, from
their proper husband.
1 Hist. «*/., vin. 32.
ANIMAL GENERATION
477
If a younger male finds a female straying
alone, he immediately pursues her, and when
she is worn out and unable to fly farther he
mounts and forces her to his pleasure.
The males all provide themselves what are
called rutting places; that is to say, they dig a
trench, or they take their stand upon an accliv-
ity, whither they compel their females to come
in turn. The female that is to be leapt stands
with her hind feet in the trench prepared for
the purpose, stooping or lowering her haunches
somewhat, if need be; by which the male is en-
abled, pressing forward upon her in the same
way as a bull, to strike her, in technical lan-
guage, and finish the business of copulation at
one assault.
Old and sturdy bucks have a considerable
number of does in their herds, as many as
ten, and even fifteen; younger and weaker
males have fewer. Keepers say that the doe
is sated with two, or at most with three leaps;
once she has conceived she admits the male no
more.
The lust of the male cools when he has served
his females; he becomes shyer, and much leaner;
he deserts his herd and roams alone, and feeds
greedily to repair his wasted strength, nor does
he afterwards approach a female for a whole
year.
When the male is capable of intercourse the
hair on his throat and neck grows black, and
the extremity of the prepuce becomes of the
same colour, and stinks abominably. The fe-
males take the male but rarely, and only in the
night or in dusky places, which are, therefore,
always chosen by the males for their connubial
pleasures. When two stags engage in battle, as
frequently happens, the vanquished yields pos-
session of his females to the victor.
EXERCISE 67. Of the constitution or change that
ta^es place in the uterus of the deer in the course of
the month of September
We now come to the changes that take place
in the genital parts of the female after inter-
course, and to the conception itself. In the
month of September, then, when the female
deer first comes in season, her cornua uteri,
uterus, or place of conception, grows somewhat
more fleshy and thick, softer also, and more
tender. In the interior of either cornu, at that
part, namely, which looks drawn together by a
band, and is turned towards the spine, we ob-
serve, protruding in regular succession, five car-
uncles, soft warts, or papillae. The first of these
is larger than any of the others, and each in suc-
cession is smaller than the one before it, just as
the cornua themselves become smaller and
smaller towards their termination. Some of the
caruncles grow to the thickness of the largest
finger, and look like proud flesh; some are
white, others of a deeper red.
From the 26th to the 28th of September, and
also subsequently, in the month of October,
the uterus becomes thicker, and the carunculae
mentioned come to resemble the nipples of the
woman's breast: you might fancy them ready
to pour out milk. Having removed their apex
that I might examine their internal structure, I
found them made up of innumerable white
points compacted together, like so many bris-
tles erect, and connected by means of a certain
mucous viscidity; compressed between the fore
finger and thumb, from the base upwards, a
minute drop of blood oozed out from each
point, a fact which led me, after further inves-
tigation, to conclude that they were entirely
made up of the capillary branches of arteries.
During the season of intercourse, therefore,
the uterine vessels, particularly the arteries, are
observed to be more numerous and of larger
size; although the parts called the female testes,
as I have said above, are neither larger nor more
highly gorged with blood than before, and do
not appear to be altered in any way from their
former state.
The inner aspect of the uterus or cornua
uteri, where it is puckered into cells, is as smooth
and soft as the ventricles of the brain, or the
glans penis within the prepuce. Nothing, how-
ever, can be discovered there— neither the se-
men of the male, nor aught else having refer-
ence to the conception — during the whole of
the months of September and October, although
I have instituted repeated dissections with a
view of examining the conception at this pe-
riod. The males have been doing their duty all
the while; nevertheless, reiterated dissection
shows nothing. This is the conclusion to which
I have come, after many years of observation. I
have only occasionally found the five caruncles
so close together that they formed a kind
of continuous protuberance into the interior
of the uterus. But when, after repeated in-
spections, I still found nothing moie in the
uterus, I began to doubt, and to ask myself
whether the semen of the male could by any
possibility make its way—by attraction or in-
jection— to the seat of the conception? And
repeated examination led me to the conclu-
sion that none of the semen whatsoever reached
this seat.
478
WILLIAM HARVEY
EXERCISE 68. Of what ta\c$ place in the month of
October
Repeated dissections performed in the course
of the month of October, both before the rut-
ting season was over and after it had passed,
never enabled me to discover any blood or se-
men, or a trace of anything else, either in the
body of the uterus or in its cornua. The uterus
was only a little larger, and somewhat thicker;
and the caruncles were more tumid and florid,
and, when strongly pressed with the finger, dis-
charged small drops of blood, much in the man-
ner in which a little watery milk can be squeezed
from the nipples of a woman in the fourth
month of her pregnancy. In one or two does,
indeed, I found a green and ichorous matter,
like an abscess, filling the cavity of the uterus,
which was preternaturally extenuated; in other
respects these animals were healthy, and in as
good condition as others which I examined at
the same time.
Towards the end of October and beginning
of November, the rutting season being now
ended, and the females separating themselves
from the males, the uterus begins (in some soon-
er, in others later) to shrink in size, and the
walls of its internal cavity, inflated in appear-
ance, to bulge out; for where the cells existed
formerly there are now certain globular masses
projecting internally, which nearly fill the whole
cavity, by which the sides are brought into mu-
tual contact, and almost agglutinated, as it
seems, so that there is no interval between
them. Even as we have seen the lips of boys
who, in robbing a hive, had been stung in the
mouth, swollen and enlarged, so that the oral
aperture was much contracted, even so does the
internal surface of the uterus in the doe enlarge,
and become filled with a soft and pulpy sub-
stance, like the matter of the brain, that fills its
cavity and involves the caruncles, which, though
not larger than before, look whiter, and as if
they had been steeped in hot water, much as
the nurse's nipple appears immediately after
the infant has quitted it. And now I have not
found it possible by any compression to force
blood out of the caruncles as before.
Nothing can be softer, smoother, more deli-
cate, than the inner aspect of the uterus thus
raised into tubers. It rivals the ventricles of the
brain in softness, so that without the informa-
tion of the eye we should scarcely perceive by
the finger that we were touching any thing. When
the abdomen is laid open immediately after the
death of the animal, I have frequently seen the
uterus affected with a wavy and creeping mo-
tion, such as is perceived in the lower part of a
slug or snail whilst it is moving, as if the uterus
were an animal within an animal, and possessed
a proper and independent motion. I have fre-
quently observed a movement of the same kind
as that just described in the intestines, whilst
engaged in vivisections; and indeed such a mo-
tion can both be seen and felt in the bodies of
dogs and rabbits whilst they are alive and un-
injured. I have also observed a corresponding
motion in the testes and scrotum of men; and I
have even known women upon whom, in their
eagerness for offspring, such palpitations have
imposed. But whether the uterus in hysterical
females, by ascending, descending, and twist-
ing, experiences any such motion or not, I can-
not take upon me to declare; and whether the
brain, in its actions and conceptions, moves in
anything of a similar manner or not, though a
point difficult of investigation, I am inclined to
look upon as one by no means unworthy of
being attempted.
Shortly afterwards, the tubercular elevations
of the inner surface of the uterus that have
been mentioned begin to shrink; it is as if, los-
ing a quantity of moisture, they became less
plump. In some instances, indeed, though rare-
ly, I have observed something like purulent
matter adhering to them, such as is usually seen
on the surface of wounds and ulcers when they
are digested, as it is said, they pour out smooth
and homogeneous pus. When I first saw this
matter, I doubted whether it was the semen of
the male or not, or a substance concocted from
its purer portion. But as it was only in exceed-
ingly rare instances that I met with such mat-
ter, and as twenty days had then passed since
the doe had had any intercourse with the buck,
and further, as the matter was not viscid and
tenacious, or spumous, such as the seminal fluid
presents itself to us, but rather friable, puru-
lent looking, and inclining to yellow, I came to
the conclusion that it was the effect of accident,
a sweat or exudation in consequence of violent
exercise previous to death; just as in a catarrh
the thinner defluxion of the nose is by and by
changed into a thicker mucus.
Having frequently shown this alteration in
the uterus to his majesty the king as the first
indication of pregnancy, and satisfied him at
the same time that there was nothing in the
shape of semen or conception to be found in the
cavity of the organ, and he had spoken of this
as an extraordinary fact to several about him, a
discussion at length arose : the keepers and hunts-
ANIMAL GENERATION
479
men asserted at first that it was but an argu-
ment of a tardy conception occasioned by the
want of rain. But by and by, when they saw
the rutting season pass away, I still continuing
to maintain that things were in the same state,
they began to say that I was both deceived my-
self and had misled the king, and that there
must of necessity be something of the concep-
tion to be found in the uterus. These men, how-
ever, when I got them to bring their own eyes
to the inquiry, soon gave up the point. The
physicians, nevertheless, held it among their
aSlvara — their impossibilities — that any con-
ception should ever be formed without the
presence of the semen masculinum, or some
trace remaining of a fertile intercourse within
the cavity of the womb.
That this important question might be the
more satisfactorily settled in all time to come,
his highness the king ordered about a dozen does
to be separated from the bucks towards the
beginning of October, and secluded in the in-
closure, which is called the course, at Hampton
Court, because the animal placed there has no
means of escape from the dogs let loose upon it.
Now that no one might say the animals thus
secluded retained any of the semen received
from the last connexions with the male, I dis-
sected several of them before the rutting season
had passed, and ascertained that no seminal
fluid remained in the uterus, although the oth-
ers were found to be pregnant in consequence
of the preceding intercourse — impregnated by
a kind of contagion as it appears — and duly
produced their fawns at the proper time.
In the dog, rabbit, and several other animals,
I have found nothing in the uterus for several
days after intercourse. I therefore regard it as
demonstrated that after fertile intercourse
among viviparous as well as oviparous animals,
there are no remains in the uterus either of the
semen of the male or female emitted in the act,
nothing produced by any mixture of these two
fluids, as medical writers maintain, nothing of
the menstrual blood present as "matter" in the
way Aristotle will have it; in a word, that there
is not necessarily even a trace of the conception
to be seen immediately after a fruitful union of
the sexes. It is not true, consequently, that in a
prolific connexion there must be any prepared
matter in the uterus which the semen mascu-
linum, acting as a coagulating agent, should
congeal, concoct, and fashion, or bring into a
positive generative act, or, by drying its outer
surface, include in membranes. Nothing cer-
tainly is to be seen within the uterus of the doe
for a great number of days, namely, from the
middle of September up to the i2th of No-
vember.
It appears, moreover, that all females do not
shed seminal fluid into the uterus during inter-
course; that there is no trace either of seminal
fluid or menstrual blood in the uterus of the
hind or doe, and many other viviparous ani-
mals. But as to what it is which is shed by wom-
en of warmer temperament no less than by men
during intercourse, accompanied with failure of
the powers and voluptuous sensations; whether
it be necessary to fecundation, whether it come
from the testes femininae, and whether it be
semen and prolific, is discussed by us elsewhere.
And whilst I speak of these matters, let gentle
minds forgive me, if, recalling the irreparable
injuries I have suffered, I here give vent to a
sigh. This is the cause of my sorrow: whilst in
attendance on his majesty the king during our
late troubles and more than civil wars, not only
with the permission but by command of the
Parliament, certain rapacious hands stripped
not only my house of all its furniture, but what
is subject of far greater regret with me, my
enemies abstracted from my museum the fruits
of many years of toil. Whence it has come to
pass that many observations, particularly on
the generation of insects, have perished, with
detriment, I venture to say, to the republic of
letters.
EXERCISE 69. Of what talps place in the uterus of
the doe during the month of November
Taught by the experience of many years I
can state truly that it is from the xath to the
1 4th of November that I first discover any-
thing which belongs to the future offspring in
the uterus of the hind.
I remember, indeed, that in the year of grace
1633, the signs of conception, or the commence-
ments of the embryos, made their appearance
somewhat earlier; because the weather was then
cloudy and wet. In does, too, which have rutted
six or seven days sooner than hinds, I have al-
ways discovered something of the future foetus
about the 8th or pth of November. What this
is and how it is begun I shall proceed to state.
A little before anything is perceptible, the
substance of the uterus or its horns appears less
than it was before the animals began to rut, the
white caruncles are more flaccid, as I have said,
and the protuberances of the internal coat sub-
side somewhat, and are corrugated and look
moist. For about the date above mentioned
certain mucous filaments like spiders' webs are
48o
WILLIAM HARVEY
observed drawn from the extremities, or su-
perior angles of the cornua through the middle
of either, and also through the body of the
uterus. These filaments becoming conjoined
present themselves as a membranous and gelati-
nous tunic or empty sac. Even as the plexus cho-
roides is extended through the ventricles of the
brain, is this oblong sac produced through the
whole of either horn and the intervening cavity
of the uterus, insinuating itself between the
wrinkles of the flabby internal tunic, and send-
ing delicate fibres among the afore-mentioned
rounded protuberances, being nearly in the
same manner as the pia mater dips between the
convolutions of the brain.
Within a day or two this sac becomes filled
with a clear, watery, sluggish albuminous mat-
ter, and now presents itself as a long-shaped
pudding full of fluid. It adheres by its external
glutinous matter to the containing walls of the
uterus, but so that it is still easily separated
from these; for if it be taken hold of cautiously
in the strait of the uterus, where it is constricted
in its course, it can be drawn entire out of either
horn.
The conception arrived at this stage removed
entire, presents itself with the figure of a wallet
or double pudding; externally, it is covered
with a purulent-looking matter; internally, it is
smooth, and contains in its cavity a viscid fluid
not unlike the thinner white of egg.
This is the conception of the hind and doe in
its first stage. And since it has now the nature
and state of an egg, and the definition given by
Aristotle of an egg is applicable to it, namely :
"A body from one part of which an animal is
produced, the remainder serving as nourish-
ment to that which is engendered";1 and fur-
ther, as it is the primordium of the future foe-
tus, it is therefore called the ovum, or egg of
the animal, in conformity with that passage of
the philosopher where he says: "Those animals
which engender internally have a certain ovi-
form body produced after the first conception.
For a humour is included within a delicate
membrane, such as that which you find under
the shell in the egg of the hen; wherefore the
blightings of conceptions that are apt to take
place about this period are called fluxes."2 This
conception, therefore, as we have already said
of the egg, is the true sperma or seed, compris-
ing the virtue of both sexes in itself, and is anal-
ogous to the seed of the vegetable. So that Aris-
1 History of Animals* i. 5 ; On the Generation of
Animal$% n. 9.
2 On the Generation of Animals t in. 9.
totle, describing the first conception of women,
says that it is "covered with a membrane like
an egg from which the shell has been removed" ;8
such as Hippocrates describes as having been
passed by the female pipe-player. And I have
myself frequently seen such ova, of the size of
pigeons' eggs, and containing no foetus, dis-
charged by women about the second month
after conception; when the ovum was of the
size of a pheasant's or hen's egg, the embryo
could be made out, the size of the little finger-
nail, floating within it. But the membrane sur-
rounding the conception has not yet acquired
any annexed placenta; neither is it connected
with the uterus; there is only at its upper and
blunter part a kind of delicate mossy or woolly
covering which stands for the rudiments of the
future placenta. The inner aspect is smooth and
polished, and covered with numerous ramifica-
tions of the umbilical vessels. In the third month
this ovum exceeds a goose's egg in size, and in-
cludes a perfect embryo of the length of two
fingers' breadths. In the fourth month it is
larger than an ostrich's egg. All these things I
have noted in the numerous careful dissections
of aborted ova which I have made.
In the way above indicated do the hind and
doe, affected by a kind of contagion, finally
conceive and produce primordia, of the nature
of eggs, or the seeds of plants, or the fruit of
trees, although for a whole month and more
they had exhibited nothing in the uterus, the
conception being perfected about the i8th, at
furthest the 2ist of November, and having its
seat now in the right, now in the left horn, occa-
sionally in both at once. The ovum at this time
is full of a colliquate matter, transparent, crys-
talline, similar to that fluid which in the hen's
egg we have called the colliquament or eye, of
far greater purity than that fluid in which the
embryo by and by floats, and contained within
a proper tunic of extreme tenuity, and orbicular
in form. In the middle of the ovum, vascular
ramifications and the punctum saliens — the
first or rudimentary particle of the foetus — and
nothing else, are clearly to be perceived. This is
the first genital part, which, once constituted,
is not only already possessed by the vegetative,
but also by the motive soul; and from this are
all the other parts of the foetus, each in its or-
der, generated, fashioned, disposed, and en-
dowed with life, almost in the same manner as
we have described the chick to be produced
from the colliquament of the egg.
Both of the humours mentioned are present
* History of Animals, vn. 7.
ANIMAL GENERATION
481
in the conceptions of all viviparous animals,
and are regarded by many as the excrements of
the foetus — one the urine, the other the sweat,
although neither of them has any unpleasant
taste, and they are always and at all periods
present in conceptions, even before a particle
of the foetus has been produced.
Of the membranes investing the two fluids,
of which there are only two, the outer is called
the chorion, the inner the amnion. The chorion
includes the whole conception, and extends in-
to either cornu; the amnion swimming in the
midst of the liquid of the former, is found in
one of the horns only, except in the cases where
there is a twin conception, when there is an
amnion present in each of them; just as in a
twin-fraught egg there are two colliquaments.
Where there are two foetuses consequently,
both are contained in one common conception,
in one egg, as it were, with its two separate col-
lections of crystalline fluid included. If you in-
cise the external membrane at any point, the
more turbid fluid which it contains immedi-
ately escapes from either horn of the uterus;
but the crystalline liquid in the interior of the
amnion does not escape at the same time unless
the membrane have been simultaneously im-
plicated.
The vein which is first discerned in the crys-
talline fluid within the amnion takes its rise
from the punctum saliens, and assumes the na-
ture and duty of an umbilical vessel; increasing
by degrees it expands into various ramifications
distributed through the colliquament, so that
it seems certain that the nourishment is in the
first instance derived from the colliquament
alone in which the foetus swims.
I have exhibited to his Serene Highness the
King, this point still palpitating in the uterus
laid open; it was extremely minute indeed, and
without the advantage of the sun's light falling
upon it from the side, its tremulous motions
were not to be perceived.
When the ovum with the colliquament en-
tire was placed in a silver or pewter basin filled
with tepid water, the punctum saliens became
beautifully distinct to the spectators. In the
course of the next ensuing days, a mucilage or
jelly, like a tiny worm, and having the shape
of a maggot, is found to be added; this is the
rudiment of the future body. It is divided into
two parts, one of which is the head, the other
the trunk, precisely in the same way as we have
already seen it in the generation of the chick in
ovo. The spine, like a keel, is somewhat bent;
the head is indifferently made up of three small
vesicles or globules, and swimming in transpar-
ent water grows amain, and by degrees assumes
its proper shape. There is only this to be ob-
served, that the eye in embryos of oviparous
animals is much larger and more conspicuous
than that of viviparous animals.
After the 26th of November the foetus is seen
with its body nearly perfect, in one case in the
right in another in the left horn of the uterus;
in twin cases in both horns.
At this time, too, the male embryo is readily
distinguishable from the female by means of
the organs of generation. These parts are also
very conspicuous in the human embryo, and
make their appearance at the same time as the
trachea.
Males and females are met with indifferently
in the right and left horn of the uterus. I have,
however, more frequently found females in the
right, males in the left horn; and I have made
the same observation in does that carried twins,
as well as in the sheep. It is certain, therefore,
that the right or left side has no appropriate
virtue in conferring sex; neither is the uterus,
nor yet the mother herself, the fashioner or
framer of the foetus, any more than the hen is
of the pullet in the egg which she incubates. In
the same way as the pullet is formed and fash-
ioned in the egg by an internal and inherent
agent, is the foetal form produced from the
uterine ovum of the hind and doe.
It is indeed matter of astonishment to find a
foetus formed and perfected within the amnion
in so short a space of time after the first appear-
ance of the blood and punctum saliens. On or
about the ipth or 20th day of November this
punctum first becomes visible; on the 2ist the
shapeless vermiculus or maggot that is to form
the body of the future animal is perceived; and
in the course of from six to seven days after-
wards a foetus so perfect in all its parts is seen,
that a male can be distinguished from a female
by the organs of generation, and the feet are
formed, the hooves being cleft, the whole hav-
ing a mucous consistency and a pale yellowish
colour.
The substance of the uterus begins to be ex-
tenuated immediately after the appearance of
the embryo; contrary to what takes place in
the human female, whose uterus grows every
day thicker and fleshier with the advancing
growth of the foetus. In the hind and doe, on
the other hand, the more the embryo augments
the more do the cornua of the uterus assimilate
themselves to the intestines; that horn in par-
ticular in which the foetus is contained looks
482
WILLIAM HARVEY
like a bag or pouch, and exceeds the opposite
one in dimensions.
The ovum or conception, thus far advanced,
and with its included foetus perfectly distinct,
has still contracted no adhesions to its mother's
sides: the whole can most readily be withdrawn
from the uterus, as I have ascertained with an
ovum which contained a foetus nearly the length
of the thumb. It is manifest, therefore, that the
foetus up to this period has been nourished by
the albumen alone that is contained within the
conception; in the same way as we have ascer-
tained the process to go on within the hen's egg.
The mouths of the umbilical veins are lost and
obliterated between the albumen and neigh-
bouring humours of the conception and their
containing membranes; but nowhere is there as
yet any connexion with the uterus, although
by these veins alone is nourishment supplied to
the embryo. And as in the egg the ramifications
of the veins are first sent to the colliquament
(in the same way as the roots of trees penetrate
the ground) and afterwards take their course to
the external tunic called the chorion, whereon,
for the sake of the nourishment, they are dis-
persed in an infinity of ramifications through
the albuminous fluid contained within the outer
membrane, so have I observed veins in the cho-
rion of a human abortion; and Aristotle also
states "that membrane to be crowded with
veins."1
If the foetus be single its umbilical vessels are
distributed to both horns, and a few twigs are
also sent to the intervening body of the uterus;
but if the conception be double, one in either
horn, each sends its umbilical vessels to its own
horn alone; the embryo in the right horn de-
riving nourishment from the right part of the
conception, that in the left from the left por-
tion of the same. In other respects the twin-
conception here is precisely similar to the twin-
conception of the egg.
Towards the end of November, then, all the
parts are clearly and distinctly to be distin-
guished, and the foetus is now of the size of a
large bean or nutmeg; its occiput is prominent,
as in the chick, but its eyes are smaller; the
mouth extends from ear to ear, the cheeks and
lips, as consisting of membranous parts, being
perfected at a very late period. In the foetuses
of all animals, indeed, that of man inclusive, the
oral aperture without lips or cheeks is seen
stretching from ear to ear; and this is the reason,
unless I much mistake, why so many arc born
with the upper lip divided as it is in the hare
1 History of Animals, vn. 7.
and camel, whence the common name of hare-
lip for the deformity. In the development of
the human foetus the upper lip only coalesces in
the middle line at a very late period.
I have frequently put a foetus the size of a
large bean, swimming in its extremely pure
nutritive fluid within the transparent amnion,
into a silver basin filled with the clearest water,
and have noted these particulars as most worthy
of observation: the brain of somewhat greater
consistency than white of egg, like milk mod
erately coagulated, and of an irregular shape,
and without any covering of skull, is contained
within a general investing membrane. The cer-
ebellum projects in a peak, as in the chick. The
conical mass of the heart is of a white colour,
and all the other viscera, the liver inclusive, are
white and spermatic-looking. The trunk of the
umbilical veins arises from the heart, and pass-
ing the convexity of the liver, perforates the
trunk of the vena portae, whence, advancing a
little and subdividing into a great number of
branches, it is distributed to the colliquament
and tunica choroidea in innumerable fine fila-
ments. The sides of the body ascend on either
hand from the spine, so that the thorax presents
itself in the guise of a boat or small vessel, up to
the period at which the heart and lungs are in-
cluded within its area, precisely and in all re-
spects as we have seen it in the development of
the chick. The heart, intestines, and other vis-
cera, are very conspicuous, and present them-
selves as appendages of the body, until the tho-
rax and abdomen being drawn around them,
and the roof, as it were, put on the building,
they are concealed within the compages of these
cavities. At this time the sides both of the tho-
rax and abdomen are white, gelatinous, and ap-
parently identical in structure, save that a num-
ber of slender white lines are perceived in the
walls of the thorax, as indications of the future
ribs, whereby a distinction is here made be-
tween the bony and fleshy compages of the
cavity.
I have also occasionally observed in concep-
tions of the sheep, which were sometimes twin,
sometimes single, of corresponding age and
about a finger's breadth in length, that the form
of the embryo resembled a small lizard of the
size of a wasp or caterpillar; the spine being
curved into a circle, and the head almost in
contact with the tail. In the double conceptions
both were of the same size, as if produced at
once and simultaneously; each floated distinctly
within the fluid of its own amnion; but although
one lay in the right, the other in the left horn
ANIMAL GENERATION
483
of the uterus, they were still both included in
the same double sac or wallet, both belonged to
the same ovum, and were surrounded by the
same common external fluid. The mouth was
large, but the eyes were mere points, so that
they could scarcely be seen, very different,
therefore, from what occurs among birds. The
viscera in these embryos were also pendulous
without the body, not yet inclosed within the
appropriate cavities. The outer membrane or
chorion adhered in no way to the uterus, so
that the entire conception was readily removed.
Within the substance of the chorion innumer-
able branches of the umbilical vessels were con-
spicuous, but having no connexion whatsoever
with the walls of the uterus; a circumstance to
which allusion has already been made in the
case of the deer; the distribution was in fact
very much as we have found it on the external
tunic of the hen's egg. There were but two hu-
mours, and the same number of containing tu-
nics, of which the chorion extending through
both cornua, and full of a more turbid fluid,
gave general configuration to the ovum or con-
ception. The tunica amnios again is almost in-
visible, like the tunica arachnoides of the eye,
and embraces the crystalline humour in which
the embryo floats.
The fluid of the amnion was, in proportion,
but a hundredth, or shall I say a thousandth, to
that of the chorion; although the crystalline
humour of the amnion was still in such quantity
that no one could reasonably imagine it to be
the sweat of the very small embryo that floated
within it. It was, further, extremely limpid,
and seemed to be without anything like Dad
taste or smell. It was, as we have already ob-
served of the deer, in all respects like watery
milk, and had none of the obnoxious qualities
of an excrement. I add, that if this fluid were of
an excrementitious nature it ought to increase
in quantity with the growth of the foetus. But
I have found precisely the opposite of this to
obtain in the conception of the ewe, so that
shortly before she lambs there is scarce a drop
of the fluid in question remaining. I am, there-
fore, rather inclined to regard it as aliment than
as excrement.
The internal tunic of the uterus of the ewe
is covered with caruncles innumerable, as the
heavens are with stars. These are not unlike
crabs' eyes, and I have called them by this
name; but they are smaller, like pendulous
warts, glandular and white, sticking within the
coats of the uterus, and somewhat excavated
towards the conception; otherwise than in the
deer, consequently, in which the caruncles cor-
responding to these rather project towards the
embryo. These caruncles are gorged with blood,
and their inner surface, where they regard the
conception, is perceived to be beset with black
sanguineous points. The umbilical vessels of the
embryo were not yet connected with these car-
uncles, nor did the conception itself adhere to
the uterus.
I find nothing of an allantois, of which some-
thing has been said as a tunic distinct from the
chorion, in the conception of the ewe. At a
later period, indeed, when the embryo is larger,
when the ovum or conception has contracted
adhesions with the uterus, and the umbilical
vessels have penetrated the caruncles, the cho-
rion extends farther, and at its extremities on
either side, and as it were in a couple of appen-
dices, there is a certain fluid of a yellow colour,
which you might call excrementitious, kept
separate and distinct.
The human conception scarcely differs in any
respect from an egg during the first months of
pregnancy. I have observed a clear fluid, like
the more liquid white of an egg, to be included
within an extremely delicate membrane. At
this time the placenta had not yet appeared,
and the entire conception was of the size of a
pigeon's, or perhaps a pheasant's egg. The em-
bryo itself, of the length of the little finger-nail,
and having the form of a small frog, was con-
spicuous enough. The body was broad, the oral
aperture widely cleft, the legs and arms like the
stalks of flowers just risen above the ground,
the occiput prominent, or rather forming a
vesicle appended to the rest of the head, such
as we have described the rudiments of the fu-
ture cerebellum in the chick.
In another human conception of about the
fiftieth day, the ovum was as large as a hen's or
a turkey's egg. The embryo was as long as a
large bean, the head of very large relative di-
mensions, and dominated by the cerebellum as
by a kind of crest. The brain itself was of the
consistence of curdled milk. Instead of a cra-
nium there was a coriaceous membrane, in some
places cartilaginous, and divided down the fore-
head to the roots of the nostrils; the face looked
like the muzzle of a dog. There were no ex-
ternal ears, nor any nose, yet could the rudi-
ments of the trachea passing down to the lungs,
and those of the penis, be detected. The two
auricles of the heart presented themselves like
eyes, of a black colour.
In the body of a woman who died of fever I
found an hermaphrodite embryo nearly of the
WILLIAM HARVEY
same size. The pudendum was like that of the
rabbit, the labia standing for prepuce, the nym-
phae for glans. In the upper part the root of the
penis was also apparent, and on either side for
the testicle there was the lax skin of the scro-
tum. The uterus was extremely diminutive,
and in figure like that of the ewe or mole, with
two horns. And as the prostate glands are situ-
ated near the penis of the boy, so were the tes-
ticles (ovaries) of visible dimensions, seen ad-
jacent to these cornua. Externally considered,
the sex seemed that of the male; internally,
however, it was rather that of the female. The
uterus of the mother was of great size, having
the urinary bladder connected with it as an ap-
pendage. In the embryo, on the contrary, the
bladder was large with the uterus of very small
dimensions attached to it.
All the human ova that have been described
above were, like those of the ewe, shaggy ex-
ternally, and besmeared with a kind of gela-
tine, or glutinous matter. At this epoch, too,
there was neither any placenta apparent, nor
any visible connexion with the uterus; neither
was there any implantation into the substance
of the uterus of the umbilical vessels scattered
over the surface of the conception itself.
As in the deer, so in the sheep, goat, and other
bisulcated animals, do we find more than one
foetus in the same conception, just as in twin-
fraught eggs we find two chicks surrounded by
the same albumen. But in the dog, rabbit, hog,
and other viviparous animals that produce a
considerable number at a litter, the thing is
otherwise. In these each foetus has two hu-
mours, these being severally surrounded with
their proper membranes.
In the bitch there are a number of knots or
constrictions along the whole course of either
cornu of the uterus, between each of which the
appropriate humours and a single embryo are
contained. In the hare and rabbit we observe
a number of balls, like the eggs of serpents, so
that the horns of the uterus look like a pair of
bracelets composed of so many amber beads
strung upon a thread. The conception of the
hare bears a strong resemblance to an acorn, the
placenta embracing the embryo like a cup, and
the humours inclosed in their membranes de-
pending like the gland or nut.
EXERCISE 70. Of the conception of the deer in the
course of the month of December
In the beginning of December the foetus is
seen larger, every way more perfect, and the
length of the finger. The heart and other viscera
which formerly hung externally are now con-
cealed within the cavities of the body, so that
they can no longer be seen without dissection.
The conception, or ovum, by the medium of
the five caruncles which we have already spoken
of as present in either cornu, is now in connex-
ion with the uterus at an equal number of
points; still the union is not so strong but that a
very slight rather than a great effort suffices to
break it. When the conception is detached, we
perceive points or depressions on the surface of
the chorion at the places where the adhesions
to the uterus had existed, these spots being fur-
ther covered with a certain viscid and wrinkled
matter, as if this had been the bond of union
between the mother and the ovum. Thus have
we the nature and use of these caruncles made
known to us: seen in the first instance as fungi
or excrescences growing from the sides of the
uterus, they are now recognized in connexion
with the conception, as standing instead of the
placenta or uterine cake in the human subject,
and performing the same office. These caruncles
are in fact but as so many nipples, whence the
embryo by means of its umbilical vessels re-
ceives the nourishment that is supplied by the
mother, as shall be clearly shown by what is to
follow.
The size and capacity of the uterus, by which
name we understand the cornua, or place occu-
pied by the conception, is increased in propor-
tion to the growth of the embryo; in suchwise,
however, that the horn in which the foetus is
lodged is larger than the other.
The conception or ovum is single, whether
one or several embryos are evolved from it;
and it extends, as already said, into both of the
horns, so that it presents itself with the 'shape
of a double pudding, or rather of a single pud-
ding having a constriction in its middle. Pro-
ceeding rounded and slender from the upper
extremity of one of the horns, the conception
gradually enlarges, and is produced into that
common cavity which in the human female is
called the uterus or matrix (because, by con-
ceiving and cherishing her offspring in this
place the woman is made a mother); the con-
ception of the deer, passing through a kind of
isthmus in the body of the uterus, is narrowed;
but by and by, escaping into the other cornu, it
there expands at first, but anon contracts again,
and finally ends as it began in a tapering ex-
tremity. The whole conception, therefore, taken
out entire, resembles a wallet filled with water
on either side; and hence the chorion is also
called alkntois, because the conception in the
ANIMAL GENERATION
485
lower animals, such as the deer, looks like an
intestine inflated, or stuffed and tied in the
middle.
In the embryo anatomized at this period
every internal part is seen distinct and perfect;
particularly the stomach, intestines, heart, kid-
neys, and lungs, which, divided into lobes, but
having the proper form of the organs, look
bloody. The colour of the lungs is deeper than
it is in those foetuses that have breathed, be-
cause the lungs, dilated by the act of respira-
tion, assume a whiter tint. And by this indica-
tion is it known whether a mother has brought
forth a living or dead child; in the former case
the colour of the lungs is changed, and the
change remains though the infant have died
immediately afterwards.
In the female foetus the testes — improperly
so called — are seen situated near the kidneys at
the extremities of the cornua uteri on either
side; they are relatively of larger size than in
the adult, and, like the caruncles of the uterus,
look white.
In the stomach of the foetus there is a watery
fluid contained, not unlike that in which it
swims, but somewhat more turbid or less trans-
parent. It resembles the milk that begins to be
secreted in the breasts of pregnant women about
the fourth or fifth month of pregnancy, and
may be pressed out of the nipples, or it is like
the drink which we call white posset.
In the small intestines there is an abundance
of chyle concocted from the same matter; in
the colon greenish faeces and scybala begin to
appear.
I do not find the urachus perforate; neither
do I perceive any difference between the tunica
allantoides or allantois, which is said to contain
urine, and the chorion. Neither do I detect any
urine in the secundines, but only in the bladder,
where indeed it is present in large quantity.
The bladder, of an oblong form, is situated be-
tween the umbilical arteries as they proceed
from the bifurcation of the descending aorta.
The liver is rudely sketched and almost shape-
less, as if it were a mere accidental part; it looks
like a red coloured mass of extravasated blood.
The brain, with some pretensions to regularity
of outline, is contained within the dura mater.
The eyes are concealed under the eyelids, which
are as firmly glued together as we find them in
puppies for some short time after birth, so that
I found it scarcely possible to separate them and
open the eyes. The breast- bones and ribs have a
certain degree of firmness, and the colour of the
muscles changes from white to blood red.
By the great number of dissections which I
performed in the course of this month, I was
every day confirmed in my opinion that the
carunculae of the uterus perform the office of
the placenta; they are at this time found of a
reddish colour, turgid, and of the size of wal-
nuts. The conception, which had previously
adhered to the caruncles by the medium of
mucor or glutinous matter only, now sends the
branches of its umbilical vessels into them, as
plants send their roots into the ground, by
which it is fastened and may be said to grow to
the uterus.
About the end of December the foetus is a
span long, and I have seen it moving lustily and
kicking; opening and shutting its mouth; the
heart, inclosed in the pericardium, when ex-
posed, was found pulsating strongly and visibly;
its ventricles, however, were still uniform, of
equal amplitude of cavity and thickness of
parietes; and each ending in a separate apex,
they form together a double-pointed cone.
Occasionally, I have seen the fluid contained in
the auricles of the heart, which at this time pre-
sent themselves as ample sacs filled with blood,
continuing to pulsate for some short time after
the ventricles themselves had left off con-
tracting.
The internal organs, all of which had lately
become perfect, were now larger and more con-
spicuous. The skull was partly cartilaginous,
partly osseous. The hooves were yellowish, flex-
ible, and soft, resembling those of the adult ani-
mal softened in hot water. The uterine carun-
cles, of great magnitude and like immense fun-
gi, extended over the whole cavity of the uterus,
and plainly performed the office of placentae,
for numerous and ample branches of the um-
bilical vessels penetrated their substance there
to imbibe nutritive matter for the growth of
the embryo. As in the foetus after birth, the
chyle is now carried by the mesenteric veins to
the porta of the liver.
Where there is a single foetus the umbilical
vessels are distributed to the whole of the car-
unculae, both those of the horn where the foetus
is lodged and those of the opposite horn; where
there is a pair of embryos formed, the umbilical
vessels of each only extend to the caruncles of
the horn appropriated to it.
The smaller umbilical veins in tending towards
the foetus, form larger and larger trunks by
coalescing, until at length two great canals are
formed, which in conjunction pour their blood
into the vena cava and vena portae. But the
umbilical arteries, which arise from the division
486
WILLIAM HARVEY
of the descending aorta, form two trunks of
small size, not remarkable save for their pulse:
proceeding to the boundary of the conception,
in other words, to the conjunction of the pla-
centa or carunculae with the ramifications of
the umbilical veins, they first divide into nu-
merous capillary twigs, and then are lost in
others that are invisible.
As the extremities of the umbilical veins
within the uterus terminate in the caruncles, so
the uterine vessels on the outside, which are
large and numerous, and bring the blood from
the mother towards the uterus, by means of the
vessels of the suspensory ligaments, terminate
externally on the caruncles. It is to be noted,
also, that the internal vessels are almost all
veins; the external vessels, again, are in many
instances branches of arteries. In the placenta
of the woman, if it be carefully examined im-
mediately after delivery, a much larger num-
ber of arteries than of veins, and these of larger
size, will be found dispersed on every side in
innumerable subdivisions to the very edge of
the mass. In the same kind of spongy paren-
chyma of the spleen, the number of the arteries
is also greater than that of the veins.
The exterior uterine vessels run to the uterus,
as I have said, not to the ovaries (testiculf) situ-
ated in the suspensory ligament, as some sup-
pose.
I have remarked an admirable instance of the
skill of nature, in the bulge or convexity of the
caruncles turned towards the conception: a
quantity of white and mucilaginous matter is
discovered in a number of cavities, cotyledons,
or little cups; these are all as full of this matter
as we ever see waxen cells full of honey; now
this matter, in colour, consistency, and taste, is
extremely like white of egg. On tearing the con-
ception away from the caruncles, you will per-
ceive numbers of suckers or capillary branches
of the umbilical veins, looking like lengthened
filaments, extracted at the same time from
every one of the cotyledons and pits, and from
amidst their mucilaginous contents; very much
as we see the delicate filaments of the roots of
herbs following the stem when it is pulled out
of the ground.
It is clearly ascertained from this that the ex-
tremities of the umbilical vessels are not con-
joined by any anastomosis with the extremities
of the uterine vessels; that they do not imbibe
any blood from them, but that they end and
are obliterated in that mucilaginous matter,
and from it take up their nourishment, nearly
in the same way as at an earlier period they had
sought for aliment from the albuminous hu-
mour contained within the membranes of the
conception. In the same manner, consequently,
as the chick in wo is nourished by the white of
the egg through its umbilical vessels, is the foe-
tus of the hind and doe nourished by a similar
albuminous matter laid up in these cells, and
not directly from the blood of the mother.
These carunculae might therefore with pro-
priety be called the uterine liver, or the uterine
mammae, seeing that they are organs adapted
for the preparation and concoction of that albu-
minous aliment, and fitting it for absorption by
the veins. In those viviparous animals conse-
quently that have neither caruncles nor pla-
centae, as the horse and the hog, the foetus is
nourished up to the moment of its birth by
fluids contained within the conception or ovum;
nor has the ovum in these animals at any time a
connexion with the uterus.
From all of what precedes it is manifest that
in both the classes of viviparous animals alluded
to, those, namely, that are provided with car-
unculae or cotyledons, and those that want
them, and perhaps in viviparous animals gen-
erally, the foetus in utero is not nourished other-
wise than the chick in ovo; the nutritive mat-
ter, the albumen, being of the same identical
kind in all. As in the egg the terminations of the
umbilical vessels are in the white and yelk, so
in the hind and doe, and other animals fur-
nished with uterine cotyledons like them, the
final distributions of the umbilical vessels are
sent to the humours that are included within
the conception or ovum, and to the albumen
that is stored in the cotyledons, or cup-like cav-
ities of the carunculae, where they open and
end. And this is further obvious from the fact
of the extremities of the umbilical vessels, when
they are drawn out of the afore-mentioned
mucor, looking completely white; a certain
proof that they absorb this mucilage liquefied
only, and not blood. The same arrangement
may very readily be observed to obtain in the
egg.
The human placenta is rendered uneven on
its convex surface, and where it adheres to the
uterus, by a number of tuberous projections,
and it seems indeed to adhere to the uterus by
means of these; it is not consequently attached
at every point, but at those places only where
the vessels pierce it in search of nourishment,
and at those where, in consequence of this ar-
rangement, an appearance as if of vessels broken
short off is perceived. But whether the extremi-
ties of these vessels suck up blood from the
ANIMAL GENERATION
487
uterus, or rather a certain concocted matter of
the nature of albumen, as I have described the
thing in the hind and doe, I have not yet
ascertained.
Finally, that the truth just announced may
be still more fully confirmed, it is found that
by compressing the uterine caruncles between
the fingers, about a spoonful of the nutritive
fluid in question may be obtained from each
of them, as from a nipple, unmixed with blood,
which is not obtained even with forcible pres-
sure. Moreover, the caruncle thus milked and
emptied, like a compressed sponge, contracts
and becomes flaccid, and is seen to be pierced
with a great number of holes. From every-
thing, therefore, it appears that these caruncles
are uterine mammae, or fountains and recep-
tacles of nutritive albumen.
The month of December at an end, the car-
uncles adhere less firmly to the uterus than be-
fore, and a small matter suffices to detach them.
The larger the foetus grows, indeed, the nearer
it is to its term, the more readily are the car-
uncles detached from the uterus, so that, like
ripe fruit from the tree, they slip at length from
the uterus of themselves, and as if they had
formed an original element in the conception.
Separated from the uterus you may perceive
in the prints which they leave points pouring
out blood; these are the arteries that entered
them. But if you now detach the conception
from the caruncles, no blood is effused; none
escapes, save from the ends of the vessels pro-
ceeding from the conception, although it does
seem more consonant with reason to suppose
that blood should be shed from the caruncles
than from the conception when they are for-
cibly separated. For, as the caruncles or coty-
ledons have an abundance of uterine branches
distributed to them, and they are generally be-
lieved to receive blood for the nourishment of
the foetus, we should expect that they would
appear replete with blood. Nevertheless, as I
have said, they yield no blood either under
milking or compression, and the reason of this
is that they contain albumen rather than blood,
and rather store up than prepare this matter. It
seems manifest, therefore, that the foetus in
utero is not nourished by its mother's blood,
but by this albuminous fluid duly elaborated.
It may even be perhaps that the adult animal
is not nourished immediately by the blood, but
rather by something mixed with the blood,
which serves as the ultimate aliment; as may
perhaps be more particularly shown in our
Physiology and particular treatise on the blood*
The truth of that passage of Hippocrates
where it said that "those whose acetabula or
cotyledons are full of mucor, abort,"1 has al-
ways been suspected by me; for this is no excre-
mentitious matter or cause of miscarriage, but
nourishment and a source of life. But Hippoc-
rates, by the word acetabula, perhaps, under-
stood something else than the parts so called in
the uterus of the lower animals, for they are
wanting in women; nor does the placenta in the
human subject contain any collections of albu-
minous matter in distinct cavities.
Modern medical writers, following the Ara-
bians, speak of three nutritious humours — dew,
gluten, and cambium; these Fernelius desig-
nates nutritious juices; as if he had wished to
imply that the parts of our bodies were not im-
mediately nourished by the blood as ultimate
nutriment, but by these secondary juices. The
first of them, like dew, bathes all the minutest
particles of the body on every side: this fluid,
become thicker by an ulterior concoction, and
adhering to the parts, is called gluten; finally,
altered and assimilated by the proper virtue of
the part, it is called cambium.
He who espoused such views might designate
the matter which is contained in the cotyle-
donous cavities of the deer as gluten or nutri-
tious albumen, and maintain that as the ulti-
mate nourishment destined for each of the par-
ticular parts of the foetus it was analogous to
the albumen or vitellus of the egg. For as we
but lately stated, with Aristotle, that the yelk
of the egg was analogous to milk, so do we think
it not unreasonable to assert that the matter
lodged in the cotyledons, or acetabula of the
uterine placenta, stands instead of milk to the
foetus so long as it remains in the uterus; in this
way the caruncles approve themselves a kind of
internal mammae, the nutritive matter of which,
transferred at the period of parturition to the
proper mammae, there assumes the nature of
milk, an arrangement by which the foetus is
seen to be nourished with the same food after
it has begun its independent existence, as it was
whilst it lodged in the uterus. Between the two-
coloured eggs of oviparous animals, consequent-
ly, or the eggs that consist of a white and a yelk,
and the ova or conceptions of viviparous ani-
mals, there is only this difference, that in the
former the vitellus (which is a secondary nutri-
tive matter) is prepared within the egg, and at
the period of birth, being stored within the ab-
domen of the young creature, serves it as food;
1 On the Nature of Diseases Common to Women; see
also Aphorisms, v. 45.
WILLIAM HARVEY
whilst in the latter, the nutritive juice is laid up
within acetabula, and after birth is transferred
to the mammae; so that the chick is nourished
with milk inclosed in its interior, whilst the
foetus of the viviparous animal draws its nour-
ishment from the breasts of its mother.
In the months of January, February, &c., as
nothing new or worthy of note occurs which
has not been already mentioned, (more than
the growth of the hair, teeth, horns, &c.) but
the parts only grow larger without reference to
the process of generation, it seems unnecessary
to say more upon such points at present.
I have frequently examined the conceptions
of sheep during the same intervals. These I find,
as in the deer, extending into both horns of the
uterus, and presenting the figure of a wallet or
double sausage. In several of them I found two
foetuses; in others only one: they were without
a trace of wool on the surface, and the eyelids
were so closely glued together that they could
not be opened; the hooves, however, were pres-
ent. Where there were two embryos they were
contained in the opposite horns of the uterus,
and without any regard to sex with reference to
the right or left horn, the male being sometimes
in the right, sometimes in the left, and the fe-
male the same; both, however, were, in every
instance, included within one and the same
common external membrane or chorion. The
extreme ends of this membrane were stained
on either hand with a yellow or bilious excre-
ment, and appeared to contain something tur-
bid or excrementitious in their interior.
Many caruncles, or miniature placentas of
different sizes, were discovered, and otherwise
disposed than in the hind and doe. In the sheep
they look like rounded fungi with the foot-
stalks broken off, and are contained in the coats
of the uterus; their rounded or convex aspects
are turned to the uterus (a circumstance, by
the way, common to the cow and sheep), their
concave aspects, which are the smooth ones,
being turned towards the foetus. The larger
branches of the vessels are also distributed to
the concave portion, as in the human placenta.
The branches in extension of the umbilical ves-
sels connected with the caruncles, grow pretty
firmly into them, so that when I attempted to
separate them, the rounded portion was rather
torn from the interior of the uterus than from
the ovum or conception; different, consequent-
ly, from what we observed in the deer, where
the chorion was readily detached from the coty-
ledons of the caruncles, and where the con-
vexity of the caruncle, connected with the
conception, is separable, whilst the concavity,
or rather the pedicle or root, is firmly adherent
to the uterus. In other respects the function
seems to be the same in both cases; in both the
same acetabula are discovered, and the same
viscid and albuminous mucus can be pressed
out in both, as it can also in the cow.
In the conception that contains a single foe-
tus, the umbilical vessels are distributed to the
whole of the caruncles of either horn; but the
one in which the foetus itself is contained, swim-
ming in its crystalline fluid within the amnion,
is larger than the other. In the cases where there
are two foetuses present, each has its own sepa-
rate or appropriate caruncles, and does not send
its umbilical vessels in quest of nourishment be-
yond the cornu in which it is lodged.
In male foetuses, the testes contained in the
scrotum, of large size for the age, hang exter-
nally. Female foetuses, again, have their dugs
in the same situation, furnished with nipples
like the breasts of women.
In the compound stomach of the foetus, name-
ly the omasus and abomasus, a clear fluid is dis-
covered, similar to that in which it floats; the
two liquids agreeing obviously in smell, taste,
and consistency. There is also a quantity of
chyle in the upper part of the intestinal tube ;
in the inferior portion a greenish-coloured ex-
crement and scybala, such as we find when the
animal is feeding on grass. The liver is discov-
ered of considerable size, the gall-bladder of an
oblong shape, and in some cases empty.
In so far as the order in which the several
parts are produced is concerned, we have still
found the same rule to be observed in the hind
and doe as in the egg, and we believe that the
same law obtains among viviparous animals
generally.
EXERCISE 71. Of the innate heat
As frequent mention is made in the preced-
ing pages of the calidum innatum, or innate
heat, I have determined to say a few words
here, by way of dessert, both on that subject
and on the humidum primigenium, or radical
moisture, to which I am all the more inclined
because I observe that many pride themselves
upon the use of these terms without, as I appre-
hend, rightly understanding their meaning.
There is, in fact, no occasion for searching after
spirits foreign to, or distinct from, the blood;
to evoke heat from another source; to bring
gods upon the scene, and to encumber philoso-
phy with any fanciful conceits; what we are
wont to derive from the stars is in truth pro-
ANIMAL GENERATION
489
duced at home: the blood is the only calidum
innatum, or first engendered animal heat; a
fact which so clearly appears from our observa-
tions on animal reproduction, particularly of
the chick from the egg, that it seems super-
fluous to multiply illustrations.
There is, indeed, nothing in the animal body
older or more excellent than the blood; nor are
the spirits which are distinguished from the
blood at any time found distinct from it; for
the blood without heat or spirit is no longer
blood, but cruor or gore. "The blood/* says
Aristotle, "is hot in a certain manner, in that,
namely, in virtue of which it exists as blood —
just as we speak of hot-water under a single
term; as subject, however, and in itself finally,
blood is blood, it is not hot: so that as blood is
in a certain way hot per se, so is it also in a cer-
tain way not hot per se: heat is in its essence or
nature, in the same way as whiteness is in the
essence of a white man; but where blood is by
affection or passion, it is not hot per se"1
We physicians at this time designate that as
spirit which Hippocrates called impetumfaciens,
or moving power; implying by this whatever
attempts aught by its own proper effort, and
causes motion with rapidity and force, or in-
duces action of any kind; in this sense we are
accustomed to speak of spirit of wine, spirit of
vitriol, &c. And therefore it is that physicians
admit as many spirits as there are principal parts
or operations of the body, viz., animal, vital,
natural, visual, auditory, concoctive, genera-
tive, implanted, influent, &c. &c. But the blood
is the first produced and most principal part of
the body, endowed with each and all of these
virtues, possessed of powers of action beyond all
the rest, and therefore, /car' €£ox^— in virtue
of its pre-eminence, meriting the title of spirit.
Scaliger, Fernelius, and others, giving less re-
gard to the admirable qualities of the blood,
have imagined other spirits of an aerial or ethe-
real nature, or composed of an ethereal or ele-
mentary matter, a something more excellent
and divine than the innate heat, the immediate
instrument of the soul, fitted for all the highest
duties. Now their principal motive for this was
the consideration that the blood, as composed
of elements, could have no power of action be-
yond these elements or the bodies compounded
of them. They have, therefore, feigned or im-
agined a spirit, different from the ingenerate
heat, of celestial origin and nature; a body of
perfect simplicity, most subtile, attenuated,
mobile, rapid, lucid, ethereal, participant in the
1 On the Pans of Animals, u. 3.
qualities of the quintessence. They have not,
however, anywhere demonstrated the actual
existence of such a spirit, or that it was superior
to the elements in its powers of action, or in-
deed that it could accomplish more than the
blood by itself. We, for our own part, who use
our simple senses in studying natural things,
have been unable anywhere to find anything of
the sort. Neither are there any cavities for the
production and preservation of such spirits,
either in fact or presumed by their authors.
Fernelius, indeed, has these words: "He who
has not yet completely mastered the matter
and state of the ingenerate heat, let him cast an
eye upon the structure of the body, and turn to
the arteries, and contemplate the sinuses of the
heart and the ventricles of the brain. When he
observes them empty, containing next to no
fluid, and yet feels that he must own such parts
not made in vain, or without a design, he will
soon, I conceive, be brought to conclude that
an extremely subtile aura or vapour fills them
during the life of the animal, and which, as
being of extreme lightness, vanished insensibly
when the creature died. It is for the sake of
cherishing this aura that by inspiration we take
in air, which not only serves for the refrigera-
tion of the body, by a business that might be
otherwise accomplished, but further supplies a
kind of nourishment."2
But we maintain that so long as an animal
lives, the cavities of the heart and the arteries
are filled with blood. We further believe the
ventricles of the brain to be indifferently fitted
for any so excellent office, and that they are
rather formed for secreting some excrementi-
tious matter. What shall we say, too, when we
find the brain of many animals unfurnished
with ventricles? And supposing it were true
that any kind of air or vapour was found there,
seeing that all nature abhors a vacuum, still it
does not seem over probable that it should be
of heavenly origin and possessed of such super-
lative virtues. But what we admire most of all
is that a spirit, the native of the skies, and en-
dowed with such admirable qualities, should be
nourished by our common and elementary air;
especially when we see it maintained that the
elements can do nothing that is beyond their
natural powers.
It is admitted, moreover, that the spirits are
in a perpetual state of flux, and most readily
dissipated and corrupted; nor indeed can they
endure for an instant unless renovated by due
supplies of their appropriate nutriment — they
2 Physiologia^ iv. 2.
490
WILLIAM HARVEY
as much require incessant nourishing as the
primura vivens, or first animate atom of the
body. What occasion is there, then, I ask, for
this extraneous inmate, for this ethereal heat?
when the blood is competent to perform all the
offices ascribed to it, and the spirits cannot sep-
arate from the blood even by a hair's breadth
without destruction; without the blood, in-
deed, the spirits can neither move nor pene-
trate anywhere as distinct and independent
matters. And whether they are engendered and
are fed and increased, as some suppose, from the
thinner part of the blood, or from the primi-
genial moisture, as others imagine, all still con-
fess that they are nowhere to be found apart
from the blood, but are inseparably connected
with it as the aliment that sustains them, even
as the flame of a lamp or candle is inseparably
connected with the oil or tallow that feeds it.
The tenuity, subtilty, mobility, &c. of the spir-
its, therefore, bring no kind of advantage more
than the blood, which it seems they constantly
accompany, already possesses. The blood con-
sequently suffices, and is adequate to be the
immediate instrument of the soul, inasmuch as
it is everywhere present, and moves hither and
thither with the greatest rapidity. Nor can it
be admitted that there are any other bodies or
qualities of a spiritual and incorporeal nature,
or any more divine kinds of heat, such as light,
as Caesar Cremoninus,1 a great adept in the
Aristotelian philosophy, strenuously contends
against Albert us that there are.
If it be said that these spirits reside in the
primigenial moisture as in their ultimate ali-
ment, and flow from thence through the whole
body to nourish its several parts, they propound
a simple impossibility, viz., that the ingenerate
heat, that primigenial element of the body,
nourished itself, yet serves for the nourishment
of the body at large. Upon such grounds the
thing nourished and the thing that nourishes
would be one and the same, and itself would
both nourish and be nourished; which could in
no way be effected; inasmuch as it is by no
means probable that the nourishment should
ever be mixed with the thing nourished, for
things mixed must have equal powers and mu-
tually act on one another; and, according to
Aristotle's dictum, "where there is nutrition,
there there is no mixture." But as nutrition
takes place everywhere, the nutriment is one
thing, and that which is nourished by it is an-
other, and it is altogether indispensable that
the one pass into the other,
1 Dictate, vn.
But as it is thought that the spirits, and the
ultimate or primigenial aliment, or something
else, is contained in animals, which acts in a
greater degree than the blood above the forces
of the elements, we are not sufficiently informed
what is understood by the expression, "acting
above the forces of the elements"; neither are
Aristotle's words rightly interpreted where he
says, "every virtue or faculty of the soul ap-
pears to partake of another body more divine
than those which are called elements. . . . For
there is in every seed a certain something which
causes it to be fruitful, viz., what is called heat,
and that not fire or any faculty of the kind, but
a spirit such as is contained in semen and frothy
bodies; and the nature inherent in that spirit is
responsive in its proportions to the element of
the stars. Wherefore fire engenders no animal;
neither is anything seen to be constituted of
the dense, or moist, or dry. But the heat of the
sun and of animals, and not only that which is
stored up in semen, but even that of any excre-
mentitious matter, although diverse in nature,
still contains a vital principle. For the rest, it is
obvious from this that the heat contained in
animals is not fire, neither does it derive its
origin from fire."2 Now I maintain the same
things of the innate heat and the blood; I say
that they are not fire, and neither do they de-
rive their origin from fire. They rather share
the nature of some other, and that a more di-
vine body or substance. They act by no faculty
or property of the elements; but as there is a
something inherent in the semen which makes
it prolific, and as, in producing an animal, it
surpasses the power of the elements — as it is a
spirit, namely, and the inherent nature of that
spirit corresponds to the essence of the stars —
so is there a spirit, or certain force, inherent in
the blood, acting superiorly to the powers of
the elements, very conspicuously displayed in
the nutrition and preservation of the several
parts of the animal body; and the nature, yea,
the soul in this spirit and blood, is identical with
the essence of the stars. That the heat of the
blood of animals during their lifetime, there-
fore, is neither fire, nor derived from fire, is
manifest, and indeed is clearly demonstrated
by our observations.
But that this may be made still more certain
let me be permitted to digress a little from my
subject, and, in a few words, to show what is
meant by the word "spirit," and what by the
phrases "superior in action to the forces of the
elements," "to have the properties of another
* On the Generation of Animals ', u. 3.
ANIMAL GENERATION
491
body, and that more divine than those bodies
which are called elements," and "the nature in-
herent in this spirit which answers to the essence
of the stars."
We have already had occasion to say some-
thing both of the nature of "spirit" and "the
vital principle," and we shall here enter into
the subject at greater length. There are three
bodies — simple bodies — which seem especially
entitled to receive the name, at all events, to
perform the office of "spirit," viz., fire, air, and
water, each of which, by reason of its ceaseless
flux and motion, expressed by the words flame,
wind, and flood, appears to have the properties
of life, or of some other body. Flame is the flow
of fire, wind the flow of air, stream or flood the
flow of water. Flame, like an animal, is self-
motive, self-nutrient, self-augmentative, and is
the symbol of our life. It is therefore that it is
so universally brought into requisition in re-
ligious ceremonies: it was guarded by priestesses
and virgins in the temples of Apollo and Vesta
as a sacred thing, and from the remotest antiq-
uity has been held worthy of divine worship by
the Persians and other ancient nations; as if
God were most conspicuous in flame, and spoke
to us from fire as He did to Moses of old. Air is
also appropriately spoken of as "spirit," having
received the title from the act of respiration.
Aristotle himself admits, "that there is a kind
of life, and birth, and death of the winds."1
Finally, we speak of a running stream as "living
water."
These three, therefore, inasmuch as they
have a kind of life, appear to act superiorly to
the forces of the element, and to share in a more
divine nature; they were, therefore, placed
among the number of the divinities by the
heathen. When any excellent work or process
appeared, surpassing the powers of the naked
elements, it was held as proceeding from some
more divine agent. "To act with power superior
to the powers of the elements," therefore, and,
on that account, "to share in the properties of
some more divine thing, which does not derive
its origin from the elements," appear to have
the same signification.
The blood, in like manner, "acts with powers
superior to the powers of the elements" in the
fact of its existence, in the forms of primordial
and innate heat, in semen and spirit, and its
producing all the other parts of the body in
succession; proceeding at all times with such
foresight and understanding, and with definite
ends in view, as if it employed reasoning in its
1 On the Generation of Animals, iv. 10. chapter.
acts. Now this it does not, in so far as it is ele-
mentary, and as deriving its origin from fire,
but in so far as it is possessed of plastic powers
and endowed with the gift of the vegetative
soul, as it is the primordial and innate heat, and
the immediate and competent instrument of
life. AZ/za, r6 fam/ato rov tu>Op&Trov: The
blood is the living principle of man, says Suidas;
and the same thing is true of all animals; an
opinion which Virgil seems to have wished to
express when he says:
Una eademquc via sanguisque animusque
sequuntur.
And by one path the blood and life flowed
out.
The blood, therefore, by reason of its admir-
able properties and powers, is "spirit." It is
also celestial; for nature, the soul, that which
answers to the essence of the stars, is the inmate
of the spirit, in other words, it is something
analogous to heaven, the instrument of heaven,
vicarious of heaven.
In this way all natural bodies fall to be con-
sidered under a twofold point of view, viz.,
either as they are specially regarded, and are
comprehended within the limits of their own
proper nature, or are viewed as the instruments
of some more noble agent and superior power.
For as regards their peculiar powers, there is,
perhaps, no doubt but that all things subject
to generation by birth, and to death and decay,
derive their origin from the elements, and per-
form their offices agreeably to their proper
standard; but in so far as they are the instru-
ments of a more excellent agent, and are gov-
erned by that, not acting of their own proper
nature, but by the regimen of another; there-
fore is it, therein is it, that they seem to par-
ticipate with another and more divine body,
and to surpass the powers of the ordinary
elements.
In the same way, too, is the blood the animal
heat, in so far, namely, as it is governed in its
actions by the soul; for it is celestial as subser-
vient to heaven; and divine, because it is the
instrument of God the great and good. But this
we have already spoken of above, where we
have shown that male and female were the in-
struments of the sun, heaven, and Supreme
Preserver, when they served for the generation
of the more perfect animals.
The inferior world, according to Aristotle, is
so continuous and connected with the superior
orbits, that all its motions and changes appear
to take their rise and to receive direction from
492
WILLIAM HARVEY
thence. In that world, indeed, which the Greeks
called K6<r/itos from its order and beauty, in-
ferior and corruptible things wait upon superior
and incorruptible things; but all are still sub-
servient to the will of the supreme, omnipotent,
and eternal Creator.
They, therefore, who think that nothing
composed of the elements can show powers of
action superior to the forces exercised by these,
unless they at the same time partake of some
other and more divine body, and on this ground
conceive the spirits they evoke as constituted
partly of the elements, partly of a certain ethe-
real and celestial substance — these persons, I
say, appear to me to reason indifferently. In the
first place you will scarcely find any elementary
body which in acting does not exceed its proper
powers: air and water, the winds and the ocean,
when they waft navies to either India and round
this globe, and often by opposite courses, when
they grind, bake, dig, pump, saw timber, sus-
tain fire, support some things, overwhelm oth-
ers, and suffice for an infinite variety of other
and most admirable offices — who shall say that
they do not surpass the powers of the elements ?
In like manner what does not fire accomplish ?
in the kitchen, in the furnace, in the labora-
tory, softening, hardening, melting, subliming,
changing, in an infinite variety of ways! What
shall we say of it when we see iron itself pro-
duced by its agency? — iron "that breaks the
stubborn soil, and shakes the earth with war!" —
iron that in the magnet (to which Thales there-
fore ascribed a soul) attracts other iron, "sub-
dues all other things, and seeks besides I know
not what inane," as Pliny1 says; for the steel
needle only rubbed with the loadstone still
steadily points to the great cardinal points; and
when our clocks constantly indicate the hours
of the day and night — shall we not admit that
all of these partake of something else, and that
of a more divine nature, than the elements?
And if in the domain and rule of nature so many
excellent operations are daily effected surpass-
ing the powers of the things themselves, what
shall we not think possible within the pale and
regimen of nature, of which all art is but imita-
tion? And if, as ministers of man, they effect
such admirable ends, what, I ask, may we not
expect of them, when they are instruments in
the hand of God ?
We must, therefore, make the distinction
and say, that whilst no primary agent or prime
efficient produces effects beyond its powers,
every instrumental agent may exceed its own
1 Hist. nat. xxxvi. 16.
proper powers in action; for it acts not merely
by its own virtue, but by the virtue of a su-
perior efficient.
They, consequently, who refuse such remark-
able faculties to the blood, and go to heaven to
fetch down I know not what spirits, to which
they ascribe these divine virtues, cannot know,
or at all events, cannot consider that the process
of generation, and even of nutrition, which in-
deed is a kind of generation, for the sake of
which they are so lavish of admirable proper-
ties, surpasses the powers of those very spirits
themselves, nor of the spirits only, but of the
vegetative, aye, even the sensitive, and I will
venture to add, the rational soul. Powers, did
I say? It far exceeds even any estimate we can
form of the rational soul; for the nature of gen-
eration, and the order that prevails in it, are
truly admirable and divine, beyond all that
thought can conceive or understanding com-
prehend.
That it may, however, more clearly appear
that the remarkable virtues which the learned
attribute to the spirits and the innate heat be-
long to the blood alone, besides what has al-
ready been spoken of as conspicuous in the egg
before any trace of the embryo appears, as well
as in the perfect and adult foetus, the few fol-
lowing observations are made by way of further
illustration, and for the sake of the diligent in-
quirer. The blood considered absolutely and by
itself, without the veins, in so far as it is an ele-
mentary fluid, and composed of several parts —
of thin and serous particles, and of thick and
concrete particles called cruor — possesses but
few, and these not very obvious virtues. Con-
tained within the veins, however, inasmuch as
it is an integral part of the body, and is ani-
mated, regenerative, and the immediate instru-
ment and principal seat of the soul, inasmuch,
moreover, as it seems to partake of the nature
of another more divine body, and is transfused
by divine animal heat, it obtains remarkable
and most excellent powers, and is analogous to
the essence of the stars. In so far as it is spirit,
it is the hearth, the Vesta, the household di-
vinity, the innate heat, the sun of the micro-
cosm, the fire of Plato; not because like com-
mon fire it lightens, burns, and destroys, but
because by a vague and incessant motion it pre-
serves, nourishes, and aggrandizes itself. It fur-
ther deserves the name of spirit, inasmuch as it
is radical moisture, at once the ultimate and the
proximate and the primary aliment, more abun-
dant than all the other parts; preparing for and
administering to these the same nutriment with
ANIMAL GENERATION
493
which itself is fed, ceaselessly permeating the
whole body, cherishing and keeping alive the
parts which it has fashioned and added to itself,
not otherwise assuredly than the superior stars,
the sun and moon especially, in maintaining
their own proper orbits, continually vivify the
stars that are beneath them.
Since the blood acts, then, with forces su-
perior to the forces of the elements, and exerts
its influence through these forces or virtues,
and is the instrument of the Great Workman,
no one can ever sufficiently extol its admirable,
its divine faculties. In the first place, and espe-
cially, it is possessed by a soul which is not only
vegetative, but sensitive and motive also; it
penetrates everywhere and is ubiquitous; ab-
stracted, the soul or the life too is gone, so that
the blood does not seem to differ in any respect
from the soul or the life itself (animd); at all
events, it is to be regarded as the substance
whose act is the soul or the life. Such, I say, is
the soul, which is neither wholly corporeal nor
yet wholly incorporeal; which is derived in part
from abroad, and is partly produced at home;
which in one way is part of the body, but in
another way is the beginning and cause of all
that is contained in the animal body, viz., nutri-
tion, sense, and motion, and consequently of
life and of death alike; for whatever is nour-
ished, is itself vivified, a&Avice versa. In like man-
ner, that which is abundantly nourished in-
creases; what is not sufficiently supplied shrinks;
what is perfectly nourished preserves its health;
what is not perfectly nourished falls into dis-
ease. The blood, therefore, even as the soul, is
to be regarded as the cause and author of youth
and old age, of sleep and waking, and also of
respiration; all the more and especially as the
first instrument in natural things contains the
internal moving cause within itself. It therefore
comes to the same thing, whether we say that
the soul and the blood, or the blood with the
soul, or the soul with the blood, performs all
the acts in the animal organism.
We are too much in the habit, neglecting
things, of worshipping specious names. The .
word blood, signifying a substance, which we
have before our eyes, and can touch, has noth-
ing of grandiloquence about it; but before such
titles as spirits, and calidum innatum or innate
heat, we stand agape. But the mask removed,
as the error disappears, so does the idle admira-
tion. The celebrated stone, so much vaunted
for its virtues by Pipinus to Migaldus, seems to
have filled not only them but also Thuanus, an
excellent historian, with wonder and admira-
tion. Let me be allowed to append the riddle:
"Lately," says he, "there was brought from the
East Indies to our king a stone, which we have
seen, wonderfully radiant with light and efful-
gence, the whole of which, as if burning and in
flames, was resplendent with an incredible bril-
liancy of light. Tossed hither and thither, it
filled the ambient air with beams that were
scarcely bearable by any eyes. It was also ex-
tremely impatient of the earth; if you essayed
to cover it, it forthwith and of itself burst forth
with violence, and mounted on high. No man
could by any art contain or inclose it in any
confined place; on the contrary, it appears to
delight in free and spacious places. It is of the
highest purity, of the greatest brightness, and
is without stain or blemish. It has no certain
shape, but a shape uncertain and changing every
moment. Of the most consummate beauty, it
suffers no one to touch it; and if you persist too
long or obstinately, it will do you injury, as I
have observed it repeatedly to do in no trifling
measure. If anything be by chance taken from
it by persevering efforts, it is (strange to say)
made nothing less thereby. Its custodier adds
further, that its virtues and powers are useful
in a great variety of ways, and even— especially
to kings— indispensably necessary; but these he
declines to reveal without being first paid a
large reward." The author might have added
of this stone that it was neither hard nor soft,
and exhibited a variety of forms and colours,
and had a singular trick of trembling and palpi-
tating, and like an animal— although itself in-
animate— consumed a large quantity of food
every day for its nutrition or sustenance. Fur-
ther, that he had heard from men worthy of
credit, that this stone had formerly fallen from
heaven to earth; that it was the frequent cause
of thunder and lightning, and was still occa-
sionally engendered from the solar beams re-
fracted through water.
Who would not admire so remarkable a stone,
or believe that it acted with a force superior to
the forces of the elements, that it participated
in the nature of another body, and possessed an
ethereal spirit ? especially when he found that
it responded in its proportions to the essence of
the sun. But with Fernelius1 for CEdipus, we
find the whole enigma resolving itself into
"Flame."
In the same way, did I paint the blood under
the garb of a fable, and gave it the title of the
philosopher's stone, and propose all its wonder-
ful faculties and operations in enigmatical Ian-
1 DC abdit. rcr. caus., xi. 27.
494
WILLIAM HARVEY
guage, many would doubtless think a great
deal of it; they would readily believe that it
could act with powers superior to those of the
elements, and they would not unwillingly allow
it to be possessed of another and more divine
body.
EXERCISE 72. Of the primigenial moisture
We have now dignified the blood with the
title of the innate heat; with like propriety, we
believe, that the fluid which we have called the
crystalline colliquament, from which the foetus
and its parts primarily and immediately arise,
may be designated the radical and primigenial
moisture. There is certainly nothing in the gen-
eration of animals to which this title can with
better right be given.
We call this the radical moisture, because
from it arises the first particle of the embryo,
the blood, to wit; and all the other posthumous
parts arise from it as from a root; and they are
procreated and nourished, and grow and are
preserved by the same matter.
We also call it primigenial, because it is first
engendered in every animal organism, and is,
as it were, the foundation of the rest, as may be
seen in the egg, in which it presents itself after
a brief period of incubation, as the first work of
the inherent fecundity and reproductive power.
This fluid is also the most simple, pure, and
unadulterated body, in which all the parts of
the pullet are present potentially, though none
of them are there actually. It appears that na-
ture has conceded to it the same qualities which
are usually ascribed to first matter common to
all things, viz., that potentially it be capable of
assuming all forms, but have itself no form in
fact. So the crystalline humour of the eye, in
order that it might be susceptible of all colours,
is itself colourless; and in like manner are the
media or organs of each of the senses destitute
of all the other qualities of sensible things: the
organs of smelling and hearing, and the air which
ministers to them, are without smell and sound;
the saliva of the tongue and mouth is also
tasteless.
And it is upon this argument that they main
ly rely who maintain the possibility of an in-
corporeal intellect, viz., because it is susceptible
of all forms without matter; and as the hand is
called the "instrument of instruments," so is
the intellect called "the form of forms," being
itself immaterial and wholly without form; it is,
therefore, said to be possible or potential, but
not passible.
This fluid, or one analogous to it, appears also
to be the ultimate aliment from which Aristotle
taught that the semen, or geniture, as he calls
it, is produced.1 I say the ultimate aliment,
called dew by the Arabians, with which all the
parts of the body are bathed and moistened.
For in the same way as this dew, by ulterior
•condensation and adhesion, becomes alible glu-
ten and cambium, whence the parts of the body
are constituted, so, mutatis mutandis, in the
commencement of generation and nutrition,
from gluten liquefied and rendered thinner is
formed the nutritious dew: from the white of
the egg is produced the colliquament under dis-
cussion, the radical moisture and primigenial
dew. The thing indeed is identical in either in-
stance, if any credit be accorded to our observa-
tions; and in fact neither philosophers nor phy-
sicians deny that an animal is nourished by the
same matter out of which it is formed, and is
increased by that from which it was engen-
dered. The nutritious dew, therefore, differs
from the colliquament or primigenial moisture
only in the relation of prior and posterior; the
one is concocted and prepared by the parents,
the other by the embryo itself, both juices,
however, being the proximate and immediate
aliment of animals; not indeed "first and sec-
ond," according to that dictum, "contraria ex
contrariis" but ultimate, as I have said, and as
Aristotle himself admonishes us, according to
that other dictum, "similia ex similibus augeri"
"like is necessarily increased by its like." There
is in either fluid a proximate force, in virtue of
which, no obstacles intervening, it will pass
spontaneously, or by the law of nature, into
every part of the animal body.
Such being the state of the question, it is
obvious that all controversy about the matter
of animals and their nourishment may be settled
without difficulty. For as some believe that the
semen or matter emitted in intercourse is taken
up from every part of the body, so do they de-
rive from this the resemblance of the offspring
to the parents. Aristotle has these words:
"Against the opinion of the ancients, it may be
said that as they avow the semen to be a deriva-
tive from all parts else, we believe the semen to
be disposed of itself to form every part; and
whilst they call it a colliquament, we are rather
inclined to regard it as an excrement" (he had,
however, said shortly before that he entitled
excrement the remains of the nourishment, and
colliquament that which is secreted from the
growth by a preternatural resolution); "for
that which arrives last, and is the excrement of
1 On the Generation of Animals > i. 18; rv. i.
ANIMAL GENERATION
495
what is final, is in all probability of the same
nature; in the same way as painters have very
commonly some remains of colours, which are
identical with those they have applied upon
their canvass; but anything that is consuming
and melting away is corrupt and degenerate.
Another argument that the seminal fluid is not
a colliquament, but an excrement, is this: that
animals of larger growth are less prolific, smaller
creatures more fruitful. Now there must be a
larger quantity of colliquament in larger than
in smaller animals, but less excrement; for as
there must be a large consumption of nourish-
ment in a large body, so must there be a small
production of excrement. Further, there is no
place provided by nature for receiving and
storing colliquament; it flows off by the way
that is most open to it; but there are receptacles
for all the natural excrements— the bowels for
the dry excrements, the bladder for the moist;
the stomach for matters useful; the genital or-
gans, the uterus, the mammae for seminal matter
— in which several places they collect and run
together." After this he goes on by a variety of
arguments to prove that the seminal matter
from which the foetus is formed is the same as
that which is prepared for the nutrition of the
parts at large. As if, should one require some
pigment from a painter, he certainly would not
go to scrape off what he had already laid on his
canvass, but would supply the demand from his
store, or from what he had over from his work,
which was still of the same nature as that which
he might have taken away from his picture. So
and in like manner the excrement of the ulti-
mate nutriment, or the remainder of the gluten
and dew, is carried to the genital organs and
there deposited; and this view is most accordant
with the production of eggs by the hen.
The medical writers, too, who hold all the
parts to be originally formed from the spermatic
fluid, and consequently speak of these under
the name of spermatic parts, say that the semen
is formed from the ultimate nourishment, which
with Aristotle they believe to be the blood,
being produced by the virtue of the genital
organs, and constituting the "matter1* of the
foetus. Now it is obvious enough that the egg is
produced by the mother and her ultimate nu-
triment, the nutritious dew, to wit. That clear
part of the egg, therefore, that primigenial, or
rather antegenial colliquament, is more truly to
be reputed the semen of the cock, although it
is not projected in the act of intercourse, but is
prepared before intercourse, or is gathered to-
gether after this, as happens in many animals,
and as will perhaps be stated more at length by
and by, because the geniture of the male, ac-
cording to Aristotle, coagulates.
When I sec, therefore, all the parts formed
and increasing from this one moisture, as "mat-
ter," and from a primitive root, and the rea-
sons already given combine in persuading us
that this ought to be so, I can scarcely refrain
from taunting and pushing to extremity the
followers of Empedocles and Hippocrates, who
believed all similar bodies to be engendered as
mixtures by association of the four contrary
elements, and to become corrupted by their
disjunction; nor should I less spare Democritus
and the Epicurean school that succeeded him,
who compose all things of congregations of
atoms of diverse figure. Because it was an error
of theirs in former times, as it is a vulgar error
at the present day, to believe that all similar
bodies are engendered from diverse or hetero-
geneous matters. For on this footing, nothing
even to the lynx's eye would be similar, one,
the same, and continuous; the unity would be
apparent only, a kind of congeries or heap— a
congregation or collection of extremely small
bodies; nor would generation differ in any re-
spect from an aggregation and arrangement of
particles.
But neither in the production of animals, nor
in the generation of any other "similar" body
(whether it were of animal parts, or of plants,
stones, minerals, &c.), have I ever been able to
observe any congregation of such a kind, or any
divers miscibles pre-existing for union in the
work of reproduction. For neither, in so far at
least as I have had power to perceive, or as rea-
son will carry me, have I ever been able to trace
any "similar" parts, such as membranes, flesh,
fibres, cartilage, bone, &c., produced in such
order, or as co-existent, that from these, as the
elements of animal bodies, conjoined organs or
limbs, and finally, the entire animal, should be
compounded. But, as has been already said, the
first rudiment of the body is a mere homoge-
neous and pulpy jelly, not unlike a concrete
mass of spermatic fluid; and from this, under
the law of generation, altered, and at the same
time split or multifariously divided, as by a
divine fiat, from an inorganic an organic mass
results; this is made bone, this muscle or nerve,
this a receptacle for excrementitious matter,
&c.; from a similar a dissimilar is produced; out
of one thing of the same nature several of di-
verse and contrary natures; and all this by no
transposition or local movement, as a congrega-
tion of similar particles, or a separation of heter-
496
WILLIAM HARVEY
ogencous particles is effected under the influ-
ence of heat, but rather by the segregation of
homogeneous than the union of heterogeneous
particles.
And I believe that the same thing takes place
in all generation, so that similar bodies have no
mixed elements prior to themselves, but rather
exist before their elements (these, according to
Empedocles and Aristotle, being fire, air, earth,
and water; according to chemists, salt, sulphur,
and mercury; according to Democritus, certain
atoms), as being naturally more perfect than
these. There are, I say, both mixed and com-
pound bodies prior to any of the so called ele-
ments, into which they are resolved, or in which
they end. They are resolved, namely, into these
elements according to reason rather than in
fact. The so-called elements, therefore, are not
prior to those things that are engendered, or
that originate, but are posterior rather—they
are relics or remainders rather than principles.
Neither Aristotle himself nor anyone else has
ever demonstrated the separate existence of the
elements in the nature of things, or that they
were the principles of "similar" bodies.
The philosopher,1 indeed, when he proceeds
to prove that there are elements, still seems un-
certain whether the conclusion ought to be that
they exist in esse, or only in fosse; he is of opin-
ion that in natural things they are present in
power rather than in action; and therefore does
he assert, from the division, separation, and
solution of things, that there are elements. It is,
however, an argument of no great cogency to
say that natural bodies are primarily produced
or composed of those things into which they
are ultimately resolved; for upon this principle
some things would come out composed of glass,
ashes, and smoke, into which we see them finally
1 On the Heavens, in. 3 .
reduced by fire; and as artificial distillation
cjearly shows that a great variety of vapours
and waters of different species can be drawn
from so many different bodies, the number of
elements would have to be increased to infinity.
Nor has any one among the philosophers said
that the bodies which, dissolved by art, are held
pure and indivisible in their species, are elements
of greater simplicity than the air, water, and
earth, which we perceive by our senses, which
we are familiar with through our eyes.
Nor, to conclude, do we see aught in the
shape of miscible matter naturally engendered
from fire; and it is perhaps impossible that it
should be so, since fire, like that which is alive,
is in a perpetual state of fluxion, and seeks for
food by which it may be nourished and kept in
being; in conformity with the words of Aris-
totle, that "Fire is only nourished, and is espe-
cially remarkable in this."2 But what is nour-
ished cannot itself be mingled with its nutri-
ment. Whence it follows that it is impossible
fire should be miscible. For mixture, according
to Aristotle, is the union of altered miscibles, in
which one thing is not transformed into an-
other, but two things, severally active and pas-
sive, into a third thing. Generation, however,
especially generation by metamorphosis, is the
distribution of one similar thing having under-
gone change into several others. Nor are mixed
similar bodies said to be generated from the ele-
ments, but to be constituted by them in some
certain way, solvent forces residing in them at
the same time.
These considerations, however, properly be-
long to the section of Physiology, which treats
of the elements and temperaments, where it
will be our business to speak of them more at
large.
2 On Generation and Corruption, n. 8.
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